PWM Dimmer/Motor Speed Controller

This is yet another project born of necessity. It's a simple circuit, but does exactly what it's designed to do - dim LED lights or control the speed of 12V DC motors. The circuit uses PWM to regulate the effective or average current through the LED array, 12V incandescent lamp (such as a car headlight bulb) or DC motor. The only difference between the two modes of operation is the addition of a power diode for motor speed control, although a small diode should be used for dimmers too, in case long leads are used which will create an inductive back EMF when the MOSFET switches off.

 

Photo of Completed PWM Dimmer/Speed Control

The photo shows what a completed board looks like. Dimensions are 53 x 37mm, so it's possible to install it into quite small spaces. The parts used are readily available, and many subsitiutions are available for both the MOSFET and power diode (the latter is only needed for motor speed control). The opamps should not be substituted, because the ones used were chosen for low power and their ability to swing the output to the negative supply rail. Note that if used as a motor speed controller, there is no feedback, so motor speed will change with load. For many applications where DC motors are used, constant speed regardless of load is not needed or desirable, but it is up to you to decide if this will suit your needs.

Description

First, a description of PWM is warranted. As the pot is rotated clockwise, the input voltage changes linearly with rotation. At first, the voltage is such that the comparator output is just narrow spikes, which turn the MOSFET on for a very short period. Average current is low, so connected LEDs will be quite dim, or a motor will run (relatively) slowly. As the input voltage coming from the pot increases, the MOSFET is on for longer and longer, so increasing power to the load.

figure 1 - PWM Waveform Generation

Figure 1 shows how the PWM principle works. The red trace is the triangle wave reference voltage, and the green trace is the voltage from the pot. When the input voltage is greater than the reference voltage, the MOSFET turns on, and current flows in the load. Because the frequency is relatively high (about 600Hz), we don't see any flicker from the LEDs, but the tone is audible from a motor that's PWM controlled. The PWM signal is shown in blue. The average current through the load is determined by the ratio of on-time to off-time, and when both are equal, the average current is exactly half of that which would be drawn with DC.

Figure 2 - Dimmer/Speed Controller Schematic

The circuit is shown in Figure 2. U1 is the oscillator, and generates a triangular waveform. R4 and R5 simply set a half voltage reference, so the opamps can function around a 6V centre voltage. U2A is an amplifier, and its output is a 10V peak to peak triangle wave that is used by the comparator based on U2B. This circuit compares the voltage from the pot with the triangle wave. If the input voltage is at zero, the comparator's output remains low, and the MOSFET is off. This is the zero setting. In reality, the reference triangle waveform is from a minimum of about 1.5V to a maximum of 9.5V, so there is a small section at each end of the pot's rotation where nothing happens. 

This is normal and practical, since we want a well defined off and maximum setting. Because of this range, for lighting applications, an industry standard 0-10V DC control signal can be used to set the light level. C-BUS (as well as many other home automation systems) can provide 0-10V modules that can control the dimmer. While a 1N4004 diode is shown for D2, this is only suitable if the unit is used as a dimmer. For motor speed control, a high-current fast recovery diode is needed, such as a HFA15TB60PBF ultra-fast HEXFRED diode. There are many possibilities for the diode, so you can use whatever is readily available that has suitable ratings. The diode should be rated for at least half the full load current of the motor, and the HFA15TB60PBF suggested is good for 15A continuous, so is fine with motors drawing up to 30A.

Construction

While it's certainly possible to build the dimmer on veroboard or similar, it's rather fiddly to make and mistakes are easily made. Also, be aware that because of the current the circuit can handle, you will need to use thick wires to reinforce some of the thin tracks. This is even necessary for the PCB version. Naturally, I recommend the PCB, and this is available from ESP. The board is small - 53 x 37mm, and it carries everything, including the screw terminals. The PCB is double-sided with plated-through holes, and has solder masks on both sides. The MOSFET will need a heatsink unless you are using the dimmer for light loads only. It is necessary to insulate the MOSFET from the heatsink in most cases, since the case of the transistor is the drain (PWM output).

For use at high current and possible high temperatures, the heatsink may need to be larger than expected. Although the MOSFET should normally only dissipate about 2W or so at 10A, it will dissipate a lot more if it's allowed to get hot. Switching MOSFETs will cheerfully go into thermal runaway and self destruct if they have inadequate heatsinking. You may also use an IGBT (insulated gate bipolar transistor) - most should have the same pinouts, and they do not suffer from the same thermal runaway problem as MOSFETs. As noted above, there are many different MOSFETs (or IGBTs) and fast diodes that are usable. The IRF540 MOSFET is a good choice, and being rated 27A it has a generous safety margin. There are many others that are equally suitable - in fact any switching MOSFET rated at 10A or more, and with a maximum voltage of more than 20V is quite ok.

Testing

Connect to a suitable 12V power supply. When powering up for the first time, use a 100 ohm "safety" resisor in series with the positive supply to limit the current if you have made a mistake in the wiring. The total current drain is about 2.5mA with the pot fully off, rising to 12.5mA when fully on. Most of this current is in the LED, which is also fed from the PWM supply so you can see that everything is working without having to connect a load. Make sure that the pot is fully anti-clockwise (minimum), and apply power. You should measure no more than 0.25V across the safety resistor, rising to 1.25V with the pot at maximum. If satisfactory, remove the safety resistor and install a load. High intensity LED strip lights can draw up to ~1.5A each, and this dimmer should be able to drive up to 10 of them, depending on the capabilities of the power supply and the size of the heatsink for the MOSFET.

source: sound.westhost

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Filter and Polarity Guard for AC/DC Adaptors

The circuit diagram of the filter and polarity guard for the wall AC/DC adaptor is shown in the figure. It is built around a bridge rectifier (BR1), two inductors (L1 and L2), three LEDs, and a few capacitors and resistors.

The circuit has input polarity indicators LED1 and LED2, input fuse F1, input high frequency filter, bridge rectifier BR1, output LC filter and output voltage indicator LED3. Input polarity indicators show the polarities of input AC or DC power connections at connector CON1.

LED1 indicates reverse polarity, whereas LED2 indicates correct polarity of the input signal. Irrespective of input connections, polarities of output voltage at CON2 will not change. LED3 is on when output voltage is present at CON2.

Input filter is built around capacitors C1, C2 and C3 to stop the high frequency noise at input of the device. BR1 is used to ensure that output voltage does not depend on input polarity and, consequently, has fixed polarity. At output of BR1, there is a set of capacitors for reducing ripples and noise coming from the wall adaptor. After that, L1 and L2 further reduce the ripples and noise.

Filter and Polarity Guard for AC/DC Adaptors circuits diagram

Output capacitor C9 provides good filtration at low frequencies and high output peak current. You can calculate the current capacity of this capacitor with the following relationship:

I=C×(dV/dT)

Here, I is the instantaneous current through the capacitor in amperes. C is capacitance in Farads. dV is change in voltage of capacitor in volts. dT is time interval or duration of the pulse applied on the capacitor in seconds. dV/dT is the instantaneous rate of voltage change over the capacitor as volts/second.

L1 and L2 are selected according to required output current and suppression of noise and ripples. All capacitors should be rated for at least 35V because most are designed for 19V and above.
Construction and testing

It is easy to assemble the circuit on a Veroboard. The circuit does not require any adjustments to work properly. Input fuse F1 is selected according to the wall adaptor output rating.

Using the circuit is simple. Connect output of the adaptor to CON1. Then, connect output voltage from CON2 to the load or target device.

The circuit is simple but useful for wall AC/DC adaptors where it is important to reduce ripples and noise, and improve transient response of the adaptors. It can also be used in a wide range of switching and analogue power supplies.

The circuit has been developed for 26V and 19V wall adaptors, but by replacing some components, it can be used for other wall adaptors with output voltage starting from 5V. When input polarity is fixed, the bridge can be replaced with simple diodes depending on requirement.

Sourced By : EFY Author : Petre Tzv Petrov

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Balanced Preamp Electret Microphone Circuit Diagram

Among the tasks solved with the help of electret microphones, one can distinguish the sound of large rooms (for example, conference rooms, temples, etc.) with a relatively large distance from the sound source, which requires high sensitivity and noise immunity. Industrial microphones for such purposes are quite expensive and, in addition, require an autonomous power source for the preamp.

The purpose of this development was to reduce the cost of manufacturing a highly sensitive and noise-proof microphone, without significant loss of playback quality.

The basis is the scheme [1] of a balanced preamplifier, powered directly from phantom power (+48 V) of a mixing console:

Balanced Preamp Electret Microphone Circuit Diagram

Its main disadvantage is excessive amplification, leading to clipping of the microphone-sensitive microphone inputs of the console. In addition, the electret microphone supply [2] is not rational enough, as well as the temperature-dependent displacement of the transistor bases on six diodes included as stabistors. The presence of these diodes, as well as electrolytic capacitors, increases the size of the board and does not contribute to miniaturization.

An attempt to replace diode stabilization with a reverse-shifted base-emitter junction of a planar transistor (KT315) was unsuccessful due to the increased noise (hiss) in the useful signal.

Therefore, in the subsequent stabilization was applied on the shunt regulator TL431, which demonstrated the practical absence of extraneous noise and high thermal stability of the bias voltage.

The final circuit of the electret microphone preamp is shown below.

Its features were additional collector resistors R7 and R9, about 4.5 times lowering the amplitude of the signal at the connector pins compared to the collectors of transistors VT1 and VT2, as well as setting the bias base VT2 directly from the divider connected to the control electrode of the shunt DA1 (+2.5 V). The electret microphone is powered from the cathode DA1 through the divider R3R6, so that the constant voltage on it is half the power supply (ie, +2.5 V from +5 V) and becomes equal to the voltage on the control electrode DA1. Such a microphone connection provides maximum sensitivity. It was tested in the project [3] and demonstrated its practical applicability.

The diagram is made on surface-mounted components (SMD) on a printed circuit board with dimensions 37 x 15 mm (drawing in * .lay7 format is given in the attachment):

The setting is reduced to equalizing the potentials between the contact points (shown by an arrow), which are displayed on the front side of the board by rotating the trimming resistor slider.

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Sourced By : circuitsstream.blogspot.com

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Dual-tone multiple frequency Based Food Dispenser for Aquarium

Presented here is an Arduino-based automatic fish feeding system for an aquarium. Feeding the fish is a daily task, which can become a problem if you are out of station for more than a day. This dispenser just needs to call a cellphone number followed by another number to perform a particular task, like turning on the motor to feed the fish in the aquarium. This project requires two cellphones, one for making the call and another for receiving it.


Circuit and working

The block diagram of the automatic food dispenser for an aquarium is shown in Fig. 1. The circuit diagram of the same is shown in Fig. 2. It consists of Arduino Uno board (Board1), DTMF decoder MT8870 (IC1), 5V voltage regulator 7805 (IC2), npn transistors BC547 (T1) and 2N2222 (T2), 5V relay (RL1), 12V DC motor and a few other components.

Fig. 1: Block diagram of automatic food dispensing system

Fig. 2: Circuit diagram of automatic food dispenser for aquarium

DTMF

Dual-tone multiple frequency (DTMF) is a signalling system for identifying the key or number dialed on a DTMF keypad. Generally, the keypad used is of 4×4 matrix type. Basically, DTMF is a sinusoidal tone, which is a combination of row and column frequencies, as shown in Table I.

In this project, DTMF decoder MT8870 (IC1) is used, which is powered by 5V DC supply. It is connected with an audio jack through a single transistor (T1) amplifier stage. The jack is connected to the audio port of the cellphone.

Arduino Uno

Arduino board (Board1) is connected to IC1 and RL1, as shown in the circuit diagram. Here, pins 11 through 14 of IC1 are connected with digital I/O pins 2 through 5 of Arduino. Input signals received from IC1 are processed by Arduino.

DC motor

A geared DC motor is connected to Arduino through RL1. A single-changeover relay is used here for controlling the geared DC motor.

A special arrangement is made on the shaft of the DC geared motor, which works as the dispensing unit. The food container is placed above the aquarium tank and contains sufficient food for the fish. A hole/slot is made at the bottom of the container. A suitable bottom lid for the container is attached to the shaft of the motor. A suitable slot is made in the lid, too.

Both the slots (container and lid) are of the same size. These slots are off-centred. The dispenser unit, which includes motor shaft, lid, container and slots, should be properly aligned. The proposed food dispenser assembly unit is shown in Fig. 3.

Fig. 3: Proposed food dispenser assembly unit

When the lid rotates along the motor’s shaft, the slot gets aligned with the slot of the container. As soon as the two slots are aligned, food reserved in the container falls into the aquarium tank due to self-weight.

The sequence of operations to activate the dispensing unit is shown in the block diagram.

Two cellphones are needed in this project. The receiver cellphone must be set on auto-answering mode, so that when the caller calls, it should automatically receive the call.

After a call is established, a predefined sequence of numbers on the keypad are to be pressed on the caller’s phone. This sequence is defined in Arduino program. IC1 decoder receives key-pressed DTMF signals from the caller’s cellphone and decodes it. These decoded signals are obtained on pins 11 through 14 of IC1. These input signals are processed as per Arduino program and the mathematical equations of calculation of decibel and binary values. Binary value is calculated in the program from input signals using the arithmetic equation given below.

Binary value=1000×v4+100×v3 +10×v2+v1
where, v1-v4 are outputs from MT8870 DTMF IC.

Here, keys 2 and 5 on the caller’s cellphone are used for starting and stopping the DC geared motor, respectively. The program can be modified as per requirement. Table II shows the binary value for each key.

Software

Arduino program (Aquarium_food_disp.ino) was used for this prototype. It must be uploaded to Arduino Uno. For this, Arduino IDE, which is an open source software, is needed. In the program, Arduino digital pins 2 through 5 are defined as input.

Main functions of Arduino code are explained below.

pinMode()

This configures the specified pin to behave either as input or output. (See the description of digital pins in Arduino manual for details on the functionality of pins.)
digitalWrite()

If the pin has been configured as output with pinMode(), its voltage will be set to the corresponding value, which is 5V (or 3.3V on 3.3V boards) for high, and 0V (ground) for low.
digitalRead()

This reads the value from a specified digital pin, as either high or low.
begin(). This sets the data rate in bits per second (baud) for serial data transmission. For communicating with the computer, use one of these rates: 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 28800, 38400, 57600 or 115200. You can also specify other rates.

For example, to communicate with an external component over pins 0 and 1 of Arduino, a particular baud rate may be required.

Construction and testing

An actual-size PCB layout of the food dispenser is shown in Fig. 4 and its components layout in Fig. 5. Use a geared DC motor for rotating the lid. A 12V battery (BATT.1) is used to power the transistor amplifier stage, 7805 and Arduino board. Another 12V battery (BATT.2) is used to power the geared DC motor.

Fig. 4: PCB layout of automatic food dispenser

Fig. 5: Components layout for the PCB

Connect the DTMF module and receiver phone using a 3.5mm audio jack. Make sure that the receiver phone is on auto-answering mode. Now, make a call on the receiver phone. After the call is received, press 2 on the caller phone. If communication is established successfully, RL1 will be energised and motor M1 will start rotating its shaft. The lid will rotate along with the shaft. For stopping the motor, press 5 on the caller phone.

Author: Tej Vijaykumar Patel sourced by : EFY

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DC / DC converter for USB connections

This converter is inexpensive and quick to build, it is nothing more than a DC / DC converter, its use is for USB sockets or any other device that needs a stabilized voltage 5 Volts and a maximum current of 2 amps.

With this power converter, you insert a voltage from 6 Volts to 24 Volts and have a regulated output of 5 Volts per 2 Amperes. That is, you can use a car or motorcycle battery or your vehicle's cigarette lighter as power, and you will have an outlet to charge your cell phone, camera, etc.

DC / DC converter for USB jacks

The circuit is very simple, and you may have already seen it in some project here on the site, the circuit uses only five components, a 7805 positive voltage regulator integrated circuit, a TIP42 transistor, a 5 Ohm resistor and two disk capacitors or polyester, one of .33 and the other of .1 or 330 and 100 nF.

The capacitors are filters and accompany the voltage regulator 7805. This converter works perfectly, as long as you respect a number of devices connected to it. The creator himself says it's ideal for a small USB hub that does not have large, connected devices.

DC / DC converter for USB connections Circuit

Above the electronic circuit diagram and the integrated circuit board of the converter, but because the circuit is compact, one can build the circuit without printed circuit board, ie using other ways of construction.

If you need more current, you will need to modify the circuit by adding a larger heat sink and even a more powerful transistor. The voltage regulator can be maintained since it only does the job of regulating the voltage at the base of the transistor and only a small current passes through it, requiring neither the installation of a heatsink on the 7805.

According to the creator of the project, any regulator integrated circuit of the line 78xx, 5, 6, 8 or 9 Volts can be used from a source of 12Volts.

The TIP42 was left with enough spacing around it to fit the small heat sink. The R1 resistor was calculated to maintain the maximum current through the TIP42, ie, about 2 Amperes.

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Low-Cost GPS Clock

Real-time clock (RTC) integrated circuits (ICs) are used for reasonably accurate time displays. The accuracy of RTCs mostly depends on the crystal. In a long run, a small-time deviation will be observed in the RTC circuit due to seasonal and atmospheric temperature changes. In case of a Global Positioning System (GPS) clock, the time/time stamp is received from the satellite(s) and is highly accurate. This project is based on a low-cost GPS clock using AVR ATmega8A microcontroller (MCU).

Circuit and working of Low-Cost GPS Clock

Circuit diagram of the simple and low-cost GPS clock is shown in Fig. 1. It is built around ATmega8A (IC1), NEO 6M GPS receiver module (GPS1) along with an antenna, 16×1 LCD (LCD1) and a few other components.

Fig. 1: Circuit diagram of GPS clock

NEO 6M GPS receiver module receives National Marine Electronics Association (NMEA) data continuously and transfers the same to ATmega8A MCU. The MCU processes the data and picks the date stamp from the received data string. The following data format is searched in the received data, which is used to pick the time stamp:

$GPGGA, 143621, .

The MCU checks for the keyword $GPGGA and reads the next six characters of the received string and displays it on LCD1. This process repeats in a cyclic process, and the latest time is displayed.

The time stamp received is always in Universal Time Coordinated (UTC) format, which matches with Greenwich Mean Time (GMT). To convert it to local time, add proper time constant to UTC time, which will depend on the country and city. In the program, the local time constant for Indian time is set to +5:30, but you can modify it to set a different value.

The local time constant is declared in C program as:

int ADJ[2] = {5,30};

Initial setup
After connecting the circuit, upload GPSclock.hex file to ATmega8A MCU using any AVR programmer through ISP port. Once the program is loaded, blinker LED1 will glow for one second followed by ‘NEO 6M GPS Clock’ message on LCD1. By default, it will display in UTC format.

To change to local time constant, press any switch (S2 or S3) to display the existing value. By pressing hours and minutes switch, the local time constant changes. If no switch is pressed for more than four seconds, the value is saved in EEPROM of the MCU.

The GPS module will initialise and try to connect to the satellite for data reception. This may take some time, say, three to five minutes. LCD1 will display “Connecting..” till the data is received from the satellite. Once the data is received, the time will be displayed on LCD1 in HH:MM:SS format continuously. In case GPS module is not connected, or is giving a connection error, ‘NO GPS MODULE’ message will be displayed on LCD1.

Use shorting jumpers SJ1 for 12/24-hour format and SJ2 for local/UTC time to be displayed. LED1 will indicate that the MCU is processing the received data. Potmeter VR1 is used for adjusting the contrast for LCD1.

Construction and testing
An actual-size PCB layout of low-cost GPS clock circuit is shown in Fig. 2 and its components layout is shown in Fig. 3.

Fig. 2: PCB layout of GPS clock

Fig. 3: Components layout for the PCB

Assemble the circuit on the PCB and connect 5V across CON1 to operate the circuit. Enclose the circuit in a suitable box and connect GPS1 across CON2. Connect the antenna to GPS1. Place the unit at a suitable location along with LCD1. Jumpers J1 and J2 shown in the PCB can be any conductor wires. Connect these before switching on the circuit.

Jumper setting
Connect SJ1 in 12-hour format, otherwise it will be set in 24-hour format by default. Connect SJ2 for UTC time, otherwise it will be set in local time (UTC+5.30).

For example, the time stamp received by the GPS module is 14:15:16, which is in UTC time in 24-hour format by default. Now, LCD1 will display the time as per the settings for SJ1 and SJ2, as shown in the table, assuming the local time constant as +05:30:00.

To change the local time, press minutes and hours switches (S2 and S3, respectively) during initialisation of the system when NEO 6M GPS message appears on LCD1. Change local time constant only once.

Sourced: EFU Author : Fayaz Hassan

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Two Channel RC Car Receiver

Someone anonymous left me a comment in this post asking that, since I had analyzed the transmitter, I also described the receiver. The comment I deleted, for the lack of care of its editor, but the request seemed right. A typical receiver of a cheap car made in China does not have much crumb. This I present is one that cost me between 3 and 4 euros (for those who are more familiar, about 4.5 USD).

Current Radio Control circuits

  There are three types of low-end radio controlled cars. Of course they do not have to be cars, the external form can be any. What matters is the circuit. Of course we talk about radio control at 27MHz, there are other controls that work with infrared but I will not talk about that.

  As I say, in RC models today we find only three types of circuits. Because the manufacturers are the same and barely change the schemes. The scheme depends on the channels that the car has. Channels are the independent actions you can perform.

  Diagram of a channel: These are the most basic and only have a button on the remote. They are the typical ones that nothing else turn them on the car goes forward. When we press the button it goes backwards and at the same time it rotates, to continue advancing as soon as we release the button. The circuit is very simple: a transmitter in the control and a receiver tuned in the car. As soon as the receiver picks up the command signal, it switches the address. Often the signal is not even modulated.

  Scheme of two channels: These have three states: forward, backward and stopped. They have two push buttons, one for forward and one for backward that can be independent or joined in a lever. The transmitter is an oscillator that can emit two tones of different frequencies (250Hz and 1000Hz), we already described the operation in this input. As for the receiver, the scheme is usually based on the integrated RX-3 from Silan. That is going to be the one we describe today.

  Scheme of five channels: They are the cars with functions of back-forward-turbo and left-right. In this case it is no longer comfortable to use different frequencies for each option, so digital modulation is used. Both the transmitter and the receiver use dedicated integrated. The TX-2B and the RX-2B respectively. We are not going to talk about them today

  Of course there are many more schemes. But these and their variants are the most common you will find in the bazaars. For the mid-range and modeling, especially in airplanes, other not so simple circuits are already used.

Two-channel receiver

This is the receiver of an RC car with two channels: forward / backward and stopped in the absence of signal. First let's look at the plate to get an idea:

We could reproduce the circuit from the tracks, as we did with the transmitter. But it is very boring, in addition in the datasheet of the RX-3 comes a scheme proposed by the integrated manufacturer. It is to be hoped that ours does not deviate too much and in fact it is very similar, deleting some components to save costs.

I have colored some sections so you can see them better (click to enlarge). Let's see how it works.

Section A: Radio frequency stage.

It seems that it is a regenerative receptor. The feedback is done through the 5.6kΩ resistance. These circuits apply positive feedback almost to the point of oscillating with the input signal. For how simple they are, they have very good sensitivity and selectivity characteristics. They have known each other since the earliest days of radio. The first patent is from 1914, with valves, of course.

The transmission reaches the antenna, passes through the tuned tank circuit and is amplified with the transistor. One of the diodes of the transistor also acts as an AM detector. Detecting and re-amplifying the tone with which the carrier is modulated. This type of design was used much earlier, when the cost of the transistors was very high. And that cost less than valves. The first transistor radios that came out proudly announced 6 transistors. Today the remote control that we analyze has 7, and the computer with which I write and read has several millions of miniature transistors inside.

The extracted audio tone goes to section B to be amplified

Section B: Audio amplification.

The integrated RX-3 incorporates two inverting amplifiers ready to use. The outer pins connect with what would be the equivalent of the inverter inputs.

The resistors and capacitors that make up this section are the feedback networks of both amplifiers. The first of them has an amplification of about 30dB which is greatly reduced for high frequencies by the effect of the 500pF capacitor in parallel with the resistance.

The second stage is configured with a gain of 10dB. All this grossly without counting the losses by the coupling capacitors, in series with the input resistors, which separate the direct current and only let the alternating current pass through.

The entire amplifier stage has a gain of 40dB. The detected tone is applied to pin 4 of the integrated. This is the demodulated signal input. When a 1000Hz tone arrives at this pin, pin 11 will be set high -forward- and the car will move forward. On the other hand when a tone of 250Hz arrives, the pin 9 -backward- will turn on and roll backwards

Section C: Bridge H.

When we apply tension to an engine it turns in a certain direction. If what we want is that we rotate one way or another at will we have to use a special arrangement of transistors to feed it. This circuit is called bridge H.

When the integrated applies voltage to the pin 11 -speed- the transistor Q9 goes to conduction. With it as a cascade reaction they also switch Q11 and Q13, grounding the left terminal of the motor and supplying positive voltage to the right one. And the engine will turn in one direction.

On the other hand, when pin 8 is activated -return- transistor Q8 is activated which in turn activates Q12 and Q10. Under these conditions, the left terminal of the motor would receive positive voltage while the right terminal is connected to ground. Just the reverse of the previous situation, and the engine will turn in the opposite direction.

There are variants of this scheme. In the scheme there are 5 NPN and 1 PNP transistors. However on the plate we have there are 4 NPN and 2 PNP. There are multiple possibilities but the idea is the same.

Section D: Food.

Finally, section D is the circuit power. There is not much to emphasize here. There are components that are missing in the commercial plate, for example the diode D1, which prevents against inversion of the batteries, they have saved it. As well as some filtering capacitors.

We see that the part that feeds the stage A is decoupled by a resistance of 100Ω and a capacitor. It serves so that no residual RF signal can leak into the power line and interfere with the integrated one.

In some circuits this part is not well designed, and the RF is coupled with the power supply, it can also pass through the parasitic capabilities between the tracks for example. In many cases of erratic behavior, especially with micro controllers this is the problem

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A Doorbell for the Deaf

This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties. 


A Doorbell for the Deaf Circuit Diagram :

Notes :
The circuit uses standard 2 wire doorbell cable or loudspeaker wire. In parallel with the doorbell switch, S1, is a 1N4001 diode and a 12 volt 60mA bulb. The bulb is optional, it may be useful for anyone who is slow to answer the door, all you need to do is flick a switch inside the house, and the bulb will illuminate a label saying Please Wait inside the doorbell switch or close to it. The double pole double throw switch sends the doorbell supply to the lamp, the 22 ohm resistor is there to reduce current flow, should the doorbell switch, S1 be pressed while the lamp is on. The resistor needs to be rated 10 watts, the 0.5 Amp fuse protects against short circuits.

When S2 is in the up position (shown as brown contacts), this will illuminate the remote doorbell lamp. When down, (blue contacts) this is the normal position and will illuminate the lamp inside the house. Switch S1 will then charge the 47u capacitor and operate the transistor which lights the lamp. As a door bell switch is only pressed momentarily, then the charge on the capacitor decays slowly, resulting in the lamp being left on for several seconds. If a longer period is needed then the capacitor may be increased in value.

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Voltage Inverter using IC NE 555

In many circuits we need to generate an internal adjustable voltage. This circuit shows how it is possible to use a trusty old NE555 timer IC and a bit of external circuitry to create a voltage inverter and doubler. The input voltage to be doubled is fed in at connector K1. To generate the stepped-up output at connector K2 the timer IC drives a two-stage inverting charge pump circuit.

The NE555 is configured as an astable multivibrator and produces a rectangular wave at its output, with variable mark-space ratio and variable frequency. This results in timing capacitor C3 (see circuit diagram) being alternately charged and discharged; the voltage at pin 2 (THR) of the NE555 swings between one-third of the supply voltage and two-thirds of the supply voltage.

Voltage Inverter Circuit Using IC NE555 

The output of the NE555 is connected to two voltage inverters. The first inverter comprises C1, C2, D1 and D2. These components convert the rectangular wave signal into a nega-tive DC level at the upper pin of K2. The second inverter, comprising C4, C5, D3 and D4, is also driven from the output of IC1, but uses the negative output voltage present on diode D3 as its reference potential. The consequence is that at the lower pin of output connector K2 we obtain a negative volt-age double that on the upper pin.

Now let us look at the voltage feedback arrangement, which lets us adjust this doubled negative output voltage down to the level we want. The NE555 has a control voltage input on pin 5 (CV). Normally the voltage level on this pin is maintained at two-thirds of the supply voltage by internal circuitry. The voltage provides a reference for one of the comparators inside the device. If the reference voltage on the CV pin is raised towards the supply voltage by an external circuit, the timing capacitor C3 in the astable multivibrator will take longer to charge and to discharge. As a result the frequency of the rectangle wave output from IC1 will fall, and its mark-space ratio will also fall.

The source for the CV reference voltage in this circuit is the base-emitter junction of PNP transistor T1. If the base volt-age of T1 is approximately 500 mV lower than its emitter voltage, T1 will start to conduct and thus pull the voltage on the CV pin towards the positive supply.

In the feedback path NPN transistor T2 has the function of a voltage level shifter, being wired in common-base configuration. The threshold is set by the resistance of the feedback chain comprising resistor R3 and potentiometer P1. When the emitter voltage of transistor T2 is more than approximately 500 mV lower than its base voltage it will start to conduct. Its collector then acts as a current sink. Potentiometer P1 can be used to adjust the sensitivity of the negative feedback circuit and hence the final output voltage level.Using T1 as a voltage reference means that the circuit will adjust itself to compensate not only for changes in load at K2, but also for changes in the input supply voltage. If K2 is disconnected from the load the desired output voltage will be maintained, with the oscillation frequency falling to around 150 Hz.

A particular feature of this circuit is the somewhat unconventional way that the NE555’s discharge pin (pin 7) is connected to its output (pin 3). To understand how this trick works we need to inspect the innards of the IC. Both pins are outputs, driven by internal transistors with bases both connected (via separate base resistors) to the emitter of a further transistor. The collectors of the output transistors are thus isolated from one another [1].

The external wiring connecting pins 3 and 7 together means that the two transistors are operating in parallel: this roughly doubles the current that can be switched to ground.The two oscilloscope traces show how the output voltage behaves under different circumstances. The left-hand figure shows the behaviour of the circuit with an input voltage of 9 V and a resistive load of 470 Ω connected to the lower pin of output connector K2. The figure on the right shows the situation with an input voltage of 10 V and a load of 1 kΩ on the lower pin of output connector K2. The pulse width and frequency of the rectangle wave at the output of IC1 are automatically adjusted to compensate for the differing conditions by the feedback mechanism built around T1 and T2.

Because of the voltage drops across the Darlington out-put stage in the IC (2.5 V maximum) and the four diodes (700 mV each) the circuit achieves an efficiency at full load (470 Ω between the output and ground) of approximately 50 %; at lower loads (1 kΩ) the efficiency is about 65 %.

Author : Peter Krueger -  Copyright : Elektor

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Simple Little Nightlight Circuit Diagram

Here we describe a very simple, economical and light-weight automatic nightlight that runs on 230V AC mains and can be used as a deluxe gizmo in the sleeping room of your kids. The arrangement proposed by the author is shown in Fig. 1.

Circuit diagram for the nightlight is shown in Fig. 2. It is built around three resistors (R1 through R3), two light-emitting diodes (LED1 and LED2), a light-dependent resistor (LDR1), a BC548 transistor (T1) and a capacitor (C1). Here LED1 is blue and LED2 is RGB with rainbow effect.

  Little Nightlight Circuit Diagram

The circuit operates off 230V AC, consuming very little current. The generic 5mm LDR drives the rainbow LED (LED2) through npn transistor T1. Series resistor R3 (150-ohm) limits the current through LED2. The sensor circuit ensures that the rainbow light switches on when it gets dark and off when there is ambient light. If desired, you can change its detection threshold by varying the value of 47-kilo-ohm resistor R2.

Resistor R1 (100-kilo-ohm), 1N4007 diode D1, and 4.7µF, 16V electrolytic capacitor C1 are used to down-convert the 230V AC input supply to a very low-value DC supply. The 5mm blue LED (LED1) not only works as an always-on pilot lamp but also keeps the voltage across buffer capacitor C1 close to around 3V. When the circuit is in active state (that is, in darkness), LED1 also produces a waving effect in tune with the current consumption of the entire circuitry.

The rainbow LED is a low-cost flashing LED with inbuilt driver chip. When power is applied, it flashes red, blue and green colours each for several seconds, then it slowly mixes these colours together to form other colours. Fig. 3 shows the author’s lab experiments.

Construction and testing

An actual-size PCB layout for the little nightlight is shown in Fig. 4 and its components layout in Fig. 5. After assembling the circuit, enclose it in a suitable box.

 PCB layout of little nightlight

 Components side of the PCB

Construction and testing

An actual-size PCB layout for the little nightlight is shown in Fig. 4 and its components layout in Fig. 5. After assembling the circuit, enclose it in a suitable box.

Fix CON1 so that you can connect 230V AC easily. Connect LDR1 such that light from LED1 and LED2 doesn’t fall on it. After proper assembly and connections, your little nightlight circuit is ready to use. Proposed enclosure is shown in Fig. 6.

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DC / AC Voltage Inverter 12v for 110 - 220V Circuit Diagram

This is the DC / AC Voltage Inverter 12v for 110 - 220V Simple and Powerful. Here is from a voltage inverter 12 Volts DC to 110 or 220 Volts AC. It is capable of generating a 50 or 60 Hz AC voltage (AC) with a square wave, which can feed most electronic equipment in a home.

Equipment with some types of motors will not work well with this voltage inverter and may even be damaged, so use it only on equipment that does not require AC power or that is not as sensitive to the type of wave.

Voltage Inverter

This circuit is very simple, uses less than 12 component to build a DC to AC voltage inverter.

 DC / AC Voltage Inverter 12v for 110 - 220V Circuit Diagram

The principle of this circuit is to generate a frequency between 50 and 60Hz through the integrated circuit CD 4074, this signal coming from pins 10 and 11, which are in opposite phases of 180º, these 50 Hertz pulses are taken to the IRFZ MOSFET transistors 44 that amplify these pulses giving them more current, after amplifying the pulse it is taken to the transformer generating high voltage in the secondary of 220Volts or 110 Volts AC depending on the used transformer.

The output waveform of the inverter is square and is improved almost to a "modified" wave with a Cn filter of 220nF, in my opinion the output is a square wave cropped, well away from being a sine wave.

The integrated circuit used. the CD4047 is a TTL integrated circuit that operates both in monostable mode and in steady mode. Below the CD4047 pinout.

The oscillator components of the CD4047, R1 / C1, are a capacitor (between pins 1 and 3) and a resistor (between pins 2 and 3), they will determine the output pulse width in monostable mode, and the output frequency in astable mode.

To increase the output current (power) a high current battery, more MOSFETS transistors in parallel and a compatible transformer should be used. For example, to obtain 240W output the battery used is at least 20A.

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Simple 100W HiFi Audio Amplifier Circuit Diagram

This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power supply must be symmetrical so that no electrolytic capacitors are needed at the outlet. Enhancer materials must be common and accessible to everyone. Construction and adjustment must be simple. The amplifier must be economical and efficient. The whole circuit is based on two Darlington output transistors that with the help of the input circuits give almost perfect results.

Technical specifications

Output power: 100W (RL = 4Ω, K = 0.1%) or 70W (RL = 8Ω, K = 0.1%) (continuous sinusoidal signal)

Power in relation to frequency: <10Hz-100KHz at 100W

Distortion: 0.1% at 20Hz-20KHz at 100W

Intrinsulation: 0.28% measured at 40Hz and 10KHz at a 4: 1 ratio and Pa = 100W

Signal/Noise (SIN): 70 dB

Input sensitivity: 0.775V

Input resistance: 100KΩ

Output resistance: 0.052 Ω (in 1KHz)

Minimum load: 4Ω

Power supply: 80V symmetrical (+ 40V, 0, -40V)

Current consumption: 2.5A max at RL = 4Ω

Peak current: 50mA

The circuit

The input stage, is a differential amplifier with main elements the transistors T1 and T2. Then we have a lead step with T4 whose collector is connected to the T3 emitter. This works like an adjustable Zener diode and regulates the resting current. The final step follows with two completely complementary transistors T7 and T8 (Darlington).

An advantage of the symmetrical voltage, is that the electrolytic capacitor is avoided at the circuit.

The amplifier has a fairly high input resistance that exceeds 100KΩ since before C4 we have R2, and since the input resistance of T1 is too high.

Negative feedback (both for DC and for AC) we have with resistance R6. The DC negative feedback section produces almost zero potential at the output. The feedback section AC determines the amplification and is dependent on R6, C4 and R3. The amplification is determined by the formula:

Uo/Ui = (R3 + R6)/R3 = 3420/120 = 28.5

The stage with T4 leads the T7 and T8, but because they are darlington they need very little base current, so for T4 we do not need a heatsink.

Transistor T3 together with resistors R18 and R19 stabilizes the output current of the output transistors. The voltage drop on R18 and R19 is determined by the position of P1 because it controls the collector voltage from the T3 transmitter. R11 in conjunction with C5 capacitor increases the AC boost of the drive.

The heart of the output stage is the Darlington transistors BDX66 and BDX67. At 25°C this series has the following characteristics:

    • Collector collector voltage: 100V

    • Max Collector Current: 16A

    • Maximum power absorbed: 150W

If the collector current becomes 10A then the collector voltage from the transmitter becomes 2V and the amplification at DC is about 1000. When the collector current is 5A then the voltage is between 0.4V and 0.5V and the amplification is about 4000.

With these characteristics these transistors are ideal for such circuits. Regardless of how "good" the transistors are, they need protection from short circuits.

The voltage drop on the collector resistors R18 and R19 gives us the magnitude of the collector current through the transmitter. If the current passing through the resistors R18 and R19 passes a certain limit, then they will start to drive the transistors T5 and T6 since the voltage on the dividers R16, R14 and R15, R17 parallel to R18 and R19. Thus the currents passing through the diodes D2 and D3 will reduce the base currents of T7 and T6, which will also reduce the collector currents.

The various other elements R and C serve different purposes. C1 limits the input bandwidth. This avoids a portion of noise. C3 is responsible for 3dB at 100KHz, that is to say, it is inclined to the characteristic of the frequency response. C6, C7 and C8 are Miller capacities. C9 and R20 stabilize the output. The C10 / R21, C12, C11 / R22 and C13 cut off the various peaks at the RF frequencies coming from the power supply.

Technical specifications

The circuit has no difficulty and its construction is relatively easy. With some luck, the amplifier can give 120W of power at 4Ω, but unfortunately the deformation reaches about 1%. But at 100W (again at 4Ω) the deformation is less than 0.1%.

From the following figure we see that the deformation remains constant and is less than 0.1% at frequencies from 40Hz to 20KHz. For full performance the input must be greater than 0.775V. This level is given by almost all preamplifiers. If a higher output device is used then a 10KΩ potentiometer must be fitted at the input of the amplifier.

The power supply

It is known that the performance of the amplifier depends on the quality of the power supply. The amplifier needs a symmetrical voltage of ± 40V. At full power (100W at 4Ω) the current is 2.5A and at load 8Ω with power 70W the current is 1.1A. For economy and simplicity, we use a non-stabilized power supply. By its nature, however, such a power supply will have a fluctuation in voltage.

If the power supply at full power output is 40V it means that with less power the supply voltage will tend to increase. However, since the output elements have a maximum operating voltage of 100V, which means ± 50V, the design should be done so that these limits are not exceeded. For this reason, we define the power supply voltage to ± 46V so that we also have a safety margin. However, the ± 46V only leaves a margin of 6V between maximum and minimum load. However, this means that the internal resistance of the power supply must be very small. A good way to get a little resistance is to use a good transformer.

Given the good transformer, a bridge-rectifying bridge and some electrolytic capacitors and we have the power supply we need. The fuses on each power line are used to protect the circuit from short circuits, because the T7 and T8 protection circuits are only short-lived until the fuses are blown. For stereo performance we need two amplifiers and therefore two power supplies.

Construction

Resistors R18 and R19 must have a PCB spacing of at least 5mm. This generates a good bleed and hence good heat dissipation. Transistors T7 and T8 as well as capacitors C7 and C8 are mounted on the heatsink.

The heatsink must be 1.2 ° C / W. If a heat-conducting paste is applied on both sides, then a heatsink with 1.8 ° C / W is sufficient. It is known that if more than one transistor is placed on a heatsink then we have to divide the thermal resistance of the heatsink with the number of transistors. Therefore, if both transistors (T7 and T8) are placed on a heatsink, then the type should be 0.6 ° C / W or 0.9 ° C / W.

In no case should there be direct contact of the transistor with the heatsink, because the collector is connected to the transistor cover and thus would cause short circuits. For this reason, insulators such as, for example, Mica.

Before connecting the capacitors C7 and C8 (see Fig. 4), insulate their terminals by placing eg. Plastic macaroni.

The connections to the printed circuit must be made with the shortest possible copper wire.

The input jack must be connected to an AF cable in the printed circuit (coaxial cable should be grounded). The best way to connect the ground to the amp printed box is to ground the input jack. The cable and the plug must be positioned as far as possible from the other components and cables to reduce the possibility of back-up and noise from the 220V network.

The two windings of the secondary are completely separate. That means four wires will remain in our hands. To see where we connect each one we get two in luck and unite them. Then we measure the voltage in the other two. If the voltage between them is 60V AC, then connect the two wires together with the earth of the power supply and the other two in the remaining free points. If the voltage is 0V, then we need to change one of the edges we've joined with a free one. Electrolytic capacitors must be attached (due to size) to the PCB with a plastic collar or the like.

Adjusting the amplifier

Remove F2 from the power supply after short-circuiting the input and making sure the output is not connected to anything else. Then put a multimeter in the 1A DC region at the ends of the fuse block, and with the (+) in its side with C2.

Turn the potentiometer to its end in a direction opposite to the clock. Check all connections and connect the power adapter to the network. The multimeter should point around 0A. If the reading is greater then an error must be present and you must immediately stop the power supply. In good condition the current should be about 100mA which with P1 must be set to 80mA. This means that the resting current in the power transistors will be about 50mA.

This is the whole process of adjusting the amplifier. We replace F2 fuse, after first shutting down the power supply. If an error has occurred, we can easily correct it by comparing the voltages at different points in the circuit. These voltages have been measured with the speaker connected and the input disconnected.

List of amplifier components

Resistors:

R1 = 120k | R2,R5,R6 = 3k3 | R3 = 120Ω | R4,R8 = 680Ω | R7 = 1k5 | R9 = 5k6 | Α10 = 1k2 | R11 = 2k7 | R12,R13 = 270Ω | R14,R15 = 15Ω | R16,R17 = 220Ω | R18,R19 = 1Ω/9W | R20 = 10Ω | R21,R22 = 1Ω | Ρ1 = 1k

Capacitors:

C1 = 470 pF | C2 = 10μF/63V | C3 = 150pF | C4 = 1000μ/4V | C5 = 220μ/40V | C6 = 47pF | C7,C8 = 560pF | C9 = 47nF | C10,C11 = 680nF | C12,C13 = 100nF

Semiconductors:

Τ1,Τ2 = BC556Α | Τ3,Τ5 = BC547B | Τ4 = BC639 | Τ6 = BC557B | Τ7 = BDX67B,BDX67C | Τ8 = BDX66B,BDX66C | D1 = 9V1/1.3W | D2,D3 = 1Ν4148,1Ν914,BAW62

Other:

2 heatsinks 1.2 ° C / W or 1.8 ° C / W (see text) | Insulators for power transistors (mica)

List of power supply components

Resistors:

R1, R2 = 3k3 / 1W

Capacitors:

C1 = 100nF | C2, C3 = 4700μF / 63V

Semiconductors:

D1, D2 = LED | B1 = B80C 3200/5000 Rectifier (Bridge)

Fusses:

F1 = 1.4A (approx.) | F2, F3 = 2.5A (approximately)

Other:

Toroidal transformer = Secondary 2 x 30V - 2x 3,75A | S1 = bipolar switch | Two fuses for PCB | A fuse box for 220V

Sourced by.Next.gr

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Arduino Uno Board - DC Motor Starter

Motor starter reduces the load, torque and current surge of a motor during startup. On starting, the motor takes more than five times the normal running current. This overheats the motor’s armature winding and creates a sudden voltage dip in the power supply, which can be avoided by using a motor starter. There are many types of motor starters. Here we describe an electronic DC motor starter using Arduino Uno board. This circuit controls both soft-start and soft-stop timings through pulse-width modulation (PWM).

Circuit and working

Circuit diagram of the DC motor soft-starter is shown in Fig. 1. In addition to Arduino Uno board (Board1), it uses PIC817 optocoupler (IC1), p-channel IRF9530 MOSFET (T1), 1N4007 rectifier diode (D1), 12V DC motor (M1) for testing, bi-colour LED (LED1) and a few other components.

Fig. 1: Circuit diagram of DC motor starter using Arduino Uno

Arduino Uno board is an important part of the circuit that generates PWM signals. Pushbuttons (S1 and S2) are used to soft-start and soft-stop the motor. The bi-colour LED indicates whether the motor is in soft-start or soft-stop mode.
Soft-start

When the circuit is switched on, the motor is at rest and LED1 off. When push button S1 is pressed momentarily, the voltage across the motor increases gradually and attains maximum voltage after the predetermined soft-start timing. So the motor first starts at a slow speed. In this state, LED1 emits green light. After the soft-start time, i.e., in running condition, LED1 emits orange light, indicating that the motor is running at the rated speed.
Soft-stop

If pushbutton S2 is pressed momentarily while the motor is running at the rated speed, the voltage across the motor decreases gradually and becomes zero after the soft-stop time. So the motor speed also decreases gradually and it finally stops after the soft-stop time. In this state, LED1 emits red colour. After the soft-stop time, LED1 doesn’t glow, indicating that the motor is at rest.

Arduino Uno is programmed such that if switch S1 or S2 is pressed more than once before the timing ends, it executes only once. This prevents the motor from restarting suddenly.
The circuit is isolated by an optocoupler (IC1) so that any disturbance in the motor power supply doesn’t affect the Arduino Uno board. The freewheeling diode (D1) gives additional protection over induced voltage when the motor is turned off.

The circuit’s operation is controlled using the software program loaded into the internal memory of Arduino Uno board. The program (softs.ino) is written in Arduino programming language sketch. Arduino IDE is used to compile and upload the program to the Arduino board.

Construction and testing

A PCB layout of the DC motor soft-starter is shown in Fig. 2 and its components layout in Fig. 3. After assembling the circuit on a PCB, connect CON2 to Arduino Uno board through external male-to-male jumper wires. After uploading the code to Board1, enclose the assembled PCB along with Board1 in a suitable plastic box.

The circuit works off the 5V USB power supply used for Arduino Uno board. Regulated 12V power supply is used to operate the DC motor.

Fig. 2: PCB layout of the DC motor starter using Arduino Uno

Fig. 3: Components layout for the PCB

Download PCB and component layout PDFs: click here
Further application

The circuit can be converted into an AC motor soft-starter by using thyristors in place of MOSFET T1. It can be used along with device control projects. Additional protection and closed-loop control can be included, if required. Different timings and PWM values can be set for both soft-start and soft-stop.
Download source code

Sourced by:  EFY

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