Basic RF Oscillator

This basic circuit is simple to create and the tool's are not critical . Most of them can be found in your junk parts box .The L1 antenna coil can be made by close winding 8 to 10 turns of 22 gauge insulated hookup wire around a 1/4 inch form such as a pencil .

You can exeprement with the size of the copile and the number of  turns to see how it affects the frequency and singnal out put of the oscilatter . You ought be able to pick up its signal with a standard FM radio receiver . The signal in ought be coupled by a disc capacitor of about 0.1 uF to stage in main of it .

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Basic IC MonoStable Multivibrator

This is the simple Basic IC MonoStable Multivibrator circuit diagram.

Basic LM555 Timer CIRCUIT

Part List
C2 = .01uf
IC1 = LM555 Timer
SWI = n.o. momentary switch
R1 and C1 determine lenght of
out put pulse where  t = R1 x C1
and R1 is in ohms and C1 is in farads .

by Tony van Roon

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Automatic 9-volt Battery Charger

Good care given to your NiCad batteries will ensure a long life. However, they do need to be handled and charged with special care. It is therefore important to first discharge the NiCad to 1 Volt per cell, ensure that the battery is discharged, and then start the charge cycle.

recommend a charge current of 1/10th the capacity for a duration of about 15 hours uninterrupted. In reality, we learn some hard lessons when we forget to switch the charger off after the 15 hours and find that one or more cells inside the battery no longer accept a charge. That is the very reason that the circuit above is fully automated.The only thing to do is connect the battery and press the 'Start' button. When the discharge cycle is finished the circuit switches over to charge for 15 hours. After

the 15 hours the circuits maintains a trickle charge to keep the battery 'topped-up

Before I go into the schematic details I like to explain some of the component descriptions in the schematic. Jan Hamer lives in the Netherlands and so the circuit details are based on european standards. 120E, 150E, etc. The 'E' just stands for Ohms so 120 ohm, 150 ohm. The original circuit specified the HEF type of cmos IC's which are not readily available in most of Canada. So just get any other type of CMOS chip like the MC4011, MC4020, MC4047 from Motorola. Any other type will do fine too. The BC548B is replaceble by a NTE123AP (NOTE: make sure it is the 'AP' type, the regular NTE123A is a total different transistor), ECG123AP, and the 2N3904 will work also.

Watch for the correct pin locations since the BCE may be reversed with this european type. The LM317T is a TO-220 type and replaceble with a ECG956 or NTE956. The LM339N can be replaced with a ECG834 or NTE834

Although this circuit looks quite impressive and maybe a bit difficult it is certainly not difficult to understand. The circuit needs to be hooked-up to a DC supply voltage of between 16.5 and max 17.5 volt, otherwise the CMOS IC's will go defective. Because I didn't feel like to design a seperate powersupply for this circuit

I connected it to my fully adjustable bench top power supply. First we connect a 'to-be-charged' 9-volt nicad battery to the appropriate connections. Then hook it up to the powersupply. Upon connection the 1nF capacitor starts up the two RS Flip-Flops formed by IC1a, IC1b, IC1c, IC1d, and pulls pins 3 and 10 'high' and pins 4 and 11 'low'. The clock pulses are created by the free- running multivibrator IC4. IC4's frequency is determined by the 10uF capacitors, the 220K resistor and the 100K trimpot. The clock runs continuesly but the counter behind, IC5, is not counting yet because pin 11 (the master-reset) is kept high. When the 'START' button is pressed, output pin 4 from IC1a goes high

and biases TR4, which is made visible by the Red LED (D9) which remains lit. The NiCad is now being discharged via this transistor and the 100 ohm resistor.

The 10K trimpot (at the right of the diagram) is adjusted in such a way that when the battery voltage dips below 7 volt, the output of IC3 goes LOW and the output pin 11 of IC1a HIGH. At hte same time the output pin 10 of IC1d goes LOW, and the red LED turns off.

Because output pin 11 went HIGH the green LED (D8) lights up and at the same time the voltage level rises causing the battery to be charged. The charge- current is determined by the 120 ohm, 150 ohm, and the trimpot of 1K, at the right side of IC2. Actually we could have used one resistor, but the output voltage of different brands for IC2 may differ, by about 1.25 volt. Because the charging current is devided by value of the resistors, with the trimpot the current can be adjusted to the correct value of your own 9-volt NiCad. (In my case, the battery is a 140 mA type, so the charge current should be adjusted for 14 mA (c/0.1).

At the same time the LOW of output pin 10 from IC1d starts the counter of the clock. On pin 9 of IC5 appear pulses which light up the red LED. This is implemented for two reasons, the clock-frequency can, with the 100K trimpot, be adjusted to the correct value; the red LED has to come ON for 6.59 seconds and for the same duration going OFF and except for that fact the green LED, who indicates the charge current, can be checked if the total charge-time is correct.

When the counter has reached 8192 pulses ( x 6.59 = 53985.28 sec = 14.99 hours) the output pin 3 of IC5 goes high again, transistor Tr1 activates and resets the two flip-flops to the start position.

The charging process stops and goes over to trickle charge via the 10K resistor and the D2 diode and keeps the battery topped-up.

The adjustments of the project are really very simple and nothing to worry about. Turn the walker of the 10K pot in the direction of the 12K resistor, ground connection point of 10K resistor/diode D2, like the adjustment pin of IC2, apply a voltage of 7-volt to the battery connection terminals, switch the power ON and slowly turn the pot backward until the greeen LED starts to light up. Switch OFF the power and take away the connections you made to make the adjustment.

Insert an amp-meter between the battery and the output connection and again switch the power ON. The battery will, in case it is not completely empty, totally discharged (to a safe level) and as soon as the 7 volt margin is reached goes over to the charge cycle. The charge current is at this time adjusted via the 1K trimpot (which is connected in series with the 150 Ohm resistor and in parallel with the 120 ohm resistor) accurately to the desired value.

Addendum: It is strongly recommended to include small 100nF ceramic capacitors over the powersupply lines feeding EACH CMOS IC to keep possible  interference to a negliable value.

Jan Hamer 

Copyright © 1995 - 2001 Tony van Roon

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Led Flasher with the LM3909 IC (streampowers)

Introduction

The LM3909 is an integrated circuit (IC) which will flash a light-emitting diode (LED). Using only two extra components and a battery, the circuit is cheap and has a very low current drain from a 1.5 V cell.

The circuit can be used as a novelty flasher, an indicator for a dummy alarm bell box, or it could be attached to a torch so that it could be found easily in the dark! The simple circuit

Led Flasher with the LM3909 IC Diagram

Assembly

The circuit can be built on a small piece of Veroboard (the piece shown in Figure 2 measures 15 holes by 10 strips). Using such a board, follow these instructions.

1. Depending on how far away you want the LED from the circuit board, solder a length of insulated wire to each lead of the LED. Use different colours of insulation – say, red and black, connecting the red lead to the anode (a) lead (the longer one) of the LED, and the black one to the cathode (k). Figure 2 shows these leads.

2. Cut the copper tracks as shown in Figure 2, using a 3 mm (1⁄8 inch) diameter drill, rotated between thumb and forefinger, or use the proper tool. Make absolutely sure that the tracks are completely broken!

3. Fit the IC holder in the correct position, using the cut tracks as guides, and make sure the small notch is facing towards the top of the board. Solder the pins to the copper tracks.

4. Mount the capacitor, positive end to the left, so that the positive lead is soldered to track F, which connects it to pin 2 of the IC; the negative lead is soldered to the right-hand side of track E, this being connected to pin 8 of the IC.

5. Solder on the battery leads, positive to the right, and the extended LED leads, positive downwards.

6. Check the circuit, and hold up the board to a bright light and look carefully for solder bridges between the tracks and pieces of copper swarf which may have escaped your inspection in 2 above! Remove whatever you find.

7. When all seems well, put the IC into the socket, ensuring that the notch or dot on the upper surface of the IC lines up with the notch on the holder. Line up each pin on the IC with the hole below it before pressing gently on the IC with the board supported on a firm surface.

8. Connect the battery; the LED should start to flash. The circuit is complete and working!

If you prefer, the whole circuit (battery included) can be mounted in a small plastic box, with the LED mounted on a clip and protruding through the panel. There are many other possibilities, and it is up to you to find an application for your own use.

Parts list

LM3909 Integrated circuit

IC socket 8-pin DIL BL17T

LED 5 mm diameter WL27E

100 microfarad (#F) Electrolytic capacitor (10 V) FB48C

Battery holder For AA-size cell YR59P

Battery 1.5 V AA cell

Small piece of Veroboard (15 holes by 10 strips)

Small plastic box (if required)

LED clip (if required)

Two lengths of coloured, insulated wire for LED (as required)

 source by 

basicelectronicprojectstutorials.blogspot.com

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Yes-No Indicator Has Zero Standby Current

This circuit produces a random "Yes" or "No" with a single button press - indicated by the illumination of a red or green LED. The circuit has two advantages over similar circuits. First, it uses just a single momentary contact pushbutton, so no on-off switch is required. When the pushbutton is pressed, an oscillator comprising the 10nF capacitor and 22kΩ resistor at pins 1 & 2 is almost immediately stopped by FET Q1, which pulls the oscillator's timing capacitor to the positive rail. However, the 220nF capacitor and 470kΩ resistor in the gate circuit of Q1 introduce a tenth of a second's delay, so that about 250 oscillations take place before the clock is stopped.

Due to variations in charge on the circuit's capacitors, as well as voltage and temperature variations, and the unpredictability of when the pushbutton will be pressed, randomness is assured. The circuit has a high degree of randomness because it takes advantage of a near-perfect complementary square waveform at pins 10 and 11 of the 4047 IC. The oscillator frequency (available at pin 13) is passed through an internal divide-by-2 circuit in the 4047. This appears at pin 10 (Q), and is inverted at pin 11 (Q-bar), thus assuring a near perfect 50:50 duty cycle for the two LEDs.

Yes-No Indicator Circuit Diagram

Note:
However, that the "impartiality" of the circuit is partly contingent on the value of the 10nF capacitor and on a reasonably equal current flow through both LEDs. Over five trials, the Yes-No Indicator scored 142 Yes, 158 No, with Yes falling behind No in the fourth trial. Because the circuit only works while switch S1 is pressed, standby current is zero, therefore a miniature 12V battery may be used to power it. In this case the circuit could be used thousands of times before the battery would run flat. The circuit has a further potential use. If the LEDs are omitted and a piezo (capacitive) sounder is wired directly to pins 10 and 11, it will produce a loud beep when equipment is turned on, and will continue to draw less than 0.5mA until it is switched off. The frequency of the beep may be changed by altering the value of the 10nF capacitor and its duration by altering the value of the 220nF capacitor.

Author: Thomas Scarborough - Copyright: Silicon Chip Electronics

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Maximum Minimum Voltage Indicator

This circuit indicates which of three voltages in the range from about about -4V to about +4V - at A, B and C - is the highest by lighting one of three indicator LEDs. Alternatively, it can be wired to indicate the lowest of three voltages or to indicate both the highest and lowest voltages. Op amps IC1a, IC1b & IC1c are wired as comparators, while the three indicator LEDs and their series 1kO current limiting resistors are strung across the op amp outputs to implement the appropriate logic functions.

 Maximum Minimum Voltage Indicator Circuit Diagram

For example, LED A will light only when pin 8 of IC1c is low (ie, A greater B) and pin 7 of IC1b is high (ie, A greater C). Similarly, LED B will light only when pin 8 of IC1c is high (ie, B greater A) and pin 1 of IC1a is low (ie, B greater C). LED C works in similar fashion if the voltage at C is the highest. Note that if all the LEDs and their parallel 1N4148 diodes are reversed, the circuit will indicate the lowest of the three input voltages. And if each 1N4148 diode is replaced by a LED, the circuit will indicate both the highest and lowest inputs.

Author: Andrew Partridge - Copyright: Silicon Chip

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Water Level Indicator Circuit

Simple, two-wire, remote monitoring unit, Three-LED level display, 9V battery powered

The whole project was developed on a friend's request. Its purpose was to remotely monitor the water-level in a metal tank located in the attic by means of a very simple control unit placed in the kitchen, some floors below.

Mains requirements were:

1. No separate supply for the remote circuit
2. Main and remote units connected by a thin two-wire cable
3. Simple LED display for the main unit
4. Battery operation to avoid problems related to mains supply and water proximity
5. As the circuit was battery operated a low current consumption was obviously welcomed

The very small remote unit is placed near the tank and measures the water level in three ranges by means of two steel rods. Each range will cover one third of the tank capacity:

• Almost empty - signaled by means of a red LED (D3) in the control unit display
• About half-level - signaled by means of a yellow LED (D2) in the control unit display
• Almost full - signaled by means of a green LED (D1) in the control unit displa
  

Circuit diagram:

Water-level Indicator Circuit Diagram

Circuit operation:

When the water-level is below the steel rods, no contact is occurring from the metal can and the rods, which are supported by a small insulated (wooden) board. The small circuit built around IC1 draws no current and therefore no voltage drop is generated across R5. IC2A, IC2B and Q1 are wired as a window comparator and, as there is zero voltage at input pins #2 and #5, D3 will illuminate. When the water comes in contact with the first rod, pin #13 of IC1 will go high, as its input pins #9 to #12 were shorted to negative by means of the water contact. Therefore, R4 will be connected across the full supply voltage and the remote circuit will draw a current of about 9mA. 

This current will cause a voltage drop of about 0.9V across R5 and the window comparator will detect this voltage and will change its state, switching off D3 and illuminating D2. When the water will reach the second rod, also pin #1 of IC1 will go high for the same reason explained above. Now either R3 and R4 will be connected across the full supply voltage and the total current drawing of the remote circuit will be about 18mA. The voltage drop across R5 will be now about 1.8V and the window comparator will switch off D2 and will drive D1. The battery will last very long because the circuit will be mostly in the off state. Current is needed only for a few seconds when P1 is pushed to check the water-level and one of the LEDs illuminates.

Parts:

R1 = 15K 1/4W Resistors
R2 = 15K 1/4W Resistors
R3 = 1K 1/4W Resistors
R4 = 1K 1/4W Resistors
R5 = 100R 1/4W Resistor
R6 = 47K 1/4W Resistor
R7 = 3.3K 1/4W Resistors
R8 = 3.3K 1/4W Resistors
R9 = 2.7K 1/4W Resistors
R10 = 15K 1/4W Resistors
R12 = 15K 1/4W Resistors
R13 = 3.3K 1/4W Resistors
R14 = 2.7K 1/4W Resistors
R15 = 2.7K 1/4W Resistors
D1 = 3mm Green LED
D2 = 3mm Yellow LED
D3 = 3mm Red LED
C1 = 470nF 63V Polyester or Ceramic Capacitor
J1 = Two ways output sockets
J2 = Two ways output sockets
P1 = SPST pushbutton
B1 = 9V PP3 Battery
Q1 = BC547 45V 100mA NPN Transistor
IC1 = 4012 Dual 4 input NAND gate IC
IC2 = LM393 Dual Comparator IC
Two steel rods of appropriate length

Notes:

• The two steel rods must be supported by a small insulated (wooden) board
• IC1 and R1-R4 are mounted on a small board placed near or on the steel rods support
• The two-wire cable connecting the remote circuit board to the main control board, i.e. J1 to J2, can be of any size and type (preferably thin for obvious reasons). It can be very long, if necessary.
• The circuit can be used also with non-metal tanks, provided a third steel rod having the height of the tank will be added and connected to pin #7 of IC1, R3, R4 and J1.
• The 4012 chip was chosen because it contains two gates and was at hand, but you can use two of the gates contained into 4001, 4011, 4093, 4049, 4069 etc. chips, provided all inputs of each gate are tied together and all inputs of unused gates are connected to the positive rail, leaving output pins open.

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Modem Off Indicator

 Modem Off Indicator Circuit Diagram. The modem off indicator is intended especially for serious Internet surfers. It will be seen that the circuit of the indicator cannot be much simpler, or there might be nothing left. In spite of its simplicity, it may prove to be a cost-saving device, since it shows at a glance whether the telephone line is free again after the modem has been used. This obviates high telephone charges in case for some reason the modem continues to operate. The circuit depends on the fact that there is a potential of about 40 V on the telephone line when it is not busy. This voltage drops sharply when a telephone call is being made. If, therefore, the circuit is linked to telephone terminals a and b, the lighting of the green LED shows that the line is not busy in error.

 Modem Off Indicator Circuit Diagram

The bridge rectifier ensures that the polarity of the line voltage is of no consequence. This has the additional benefit that polarity protection for the LED is not necessary. To make sure that the telephone line is not loaded unnecessarily, the LED is a high efficiency type. This type lights at a current as low as 2 mA, and this is, therefore the current arranged through it by resistor R1.

WARNING.

In spite of the liberal age we live in, it is highly probable that in many countries it is not allowed to connect the indicator across the telephone lines. Seek advice of your local telephone company that owns or operates the telephone network.

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Audio Clipping Indicator

Detects clipping in preamp stages, mixers, amplifiers etc., Single LED display - 9V Battery supply unit

This circuit was intended to be used as a separate, portable unit, to signal by means of a LED when the output wave form of a particular audio stage is "clipping" i.e. is reaching the onset of its maximum permitted peak-to-peak voltage value before an overload is occurring. This will help the operator in preventing severe, audible distortion to be generated through the audio equipment chain. 

This unit is particularly useful in signaling overload of the input stages in mixers, PA or musical instruments amplification chains, but is also suited to power amplifiers. A careful setting of Trimmer R5 will allow triggering of the LED with a wide range of peak-to-peak input voltages, in order to suit different requirements. Unfortunately, an oscilloscope and a sine wave frequency generator are required to accurately setup this circuit. Obviously, the unit can be embedded into an existing mixer, preamp or power amplifier, and powered by the internal supply rails in the 9 - 30V range. The power supply can also be obtained from higher voltage rails provided suitable R/C cells are inserted. SW1 and B1 must obviously be omitted.

Audio Clipping Indicator Circuit Diagram

Parts:
R1___________1M 1/4W Resistor (See Notes)
R2,R3,R8_____100K 1/4W Resistors
R4,R6________10K 1/4W Resistors
R5___________5K 1/2W Trimmer Cermet or Carbon
R7___________2K2 1/4W Resistor
R9___________22K 1/4W Resistor
R10__________1K 1/4W Resistor (See Notes)
C1,C4________220nF 63V Polyester Capacitors
C2___________4p7 63V Ceramic Capacitor (See Notes)
C3___________220µF 25V Electrolytic Capacitor
C5___________10µF 25V Electrolytic Capacitor (See Notes)
D1,D2________1N4148 75V 150mA Diodes
D3___________LED (Any dimension, shape and color)
Q1___________BC547 45V 100mA NPN Transistor
IC1___________TL062 Dual Low current BIFET Op-Amp (or TL072, TL082)
SW1__________SPST Toggle or Slide Switch (See Text)
B1____________9V PP3 Battery (See Text)

Circuit operation:

The heart of the circuit is a window comparator formed by two op-amps packaged into IC1. This technique allows to detect precisely and symmetrically either the positive or negative peak value reached by the monitored signal. The op-amps outputs are mixed by D1 and D2, smoothed by C4, R7 and R8, and feed the LED driver Q1 with a positive pulse. C5 adds a small output delay in order to allow detection of very short peaks.

Notes:

• With the values shown, the circuit can be easily set up to detect sine wave clipping from less than 1V to 30V peak-to-peak (i.e. 15W into 8 Ohms). If you need to detect higher output peak-to-peak voltages, R1 value must be raised. On the contrary, if the circuit will be used to detect only very low peak-to-peak voltages, it is convenient to lower R1 value to, say, 220K omitting C2. In this way, the adjustment of R5 will be made easier.
• Using a TL062 chip at 9V supply, stand-by current drawing is about 1.5mA and less than 10mA when the LED illuminates. With TL072 or TL082 chips, current drawing is about 4.5mA and 13mA respectively.
• When using power supplies higher than 12V, the value of R10 must be raised accordingly.
• When using power supplies higher than 25V, the working voltage value of C5 must be raised to 35 or 50V.

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110 and 220V AC LED Voltage Indicator

110 and 220V AC LED Voltage Indicator Circuit Diagram. Useful for power lines control, Simple, transformer less circuitry. This circuit, designed on request, has proven to be useful to indicate when the voltage in a power supply line is changing from 120V to 240Vac. It can be used in different circumstances and circuits, mainly when an increase in ac or dc supply voltage needs to be detected. D3 illuminates when the line voltage is approaching 120V and will remain in the on state also at 240V supply. On the other hand, D6 will illuminate only when the line voltage is about 240V and will stay on because the latching action of Q1, Q2 and related components. C1, D1 and D2 provide a low dc voltage in the 4.5V - 6V range in order to allow proper operation of latch circuit and LEDs.

Circuit diagram:

110 and 220V AC LED Voltage Indicator Circuit Diagram

Parts:
R1__________470R 1/2W Resistor
R2__________220K 1/4W Resistor
R3,R7_______470R 1/4W Resistors
R4__________1K 1/4W Resistor
R5__________2K2 1/4W Resistor
R6_________330R 1/4W Resistor
C1_________330nF 630V Polyester Capacitor
C2_________10µF 25V Electrolytic Capacitor
D1,D2______N4007 1000V 1A Diode
D3,D6______LEDs (Color and shape at will)
D4_________BZX79C10 10V 500mW Zener Diode (See Notes)
D5_________1N4148 75V 150mA Diode
Q1_________BC547 45V 100mA NPN Transistor
Q2_________BC557 45V 100mA PNP Transistor

Notes:

• D4 value could require some adjustment in order to allow precise switching of the circuit at the chosen voltage. If the case, please try values in the 8.2V - 15V range.
• Warning! The circuit is connected to 240Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.

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Clipping Indicator For Audio Amplifiers

A clipping indicator is a useful accessory on any audio amplifier. It indicates when the amplifier has reached its limit and is clipping the peaks of the audio signal. In practice, quite a lot of clipping can occur before you can hear it. So why is it necessary to know when an amplifier is clipping if you can't notice it? The answer is that clipping "squares up" the waveform and square waves contain lots of higher-frequency harmonics which can easily damage the tweeters in loudspeaker systems. This circuit is a true clipping indicator as opposed to the level indicators that are commonly used in preamplifier stages.

The problem with level indicators is that an amplifier's maximum output power is not constant. That's because the amplifier's supply rails are not regulated and so the maximum power available at any given instant varies, depending on the applied signal. The circuit is quite simple and is based on two BD140 PNP transistors and zener diode ZD1. During normal operation, Q1 is turned on via ZD1 and R1. As a result, Q2 is held off (since its base is pulled high) and so LED1 is also off. However, if the output signal subsequently rises to within 4.7V of the positive supply rail, Q1 turns off since it no longer has any forward bias on its base.

Clipping Indicator Circuit Diagram

As a result Q2's base is now pulled low via R2 and so Q2 turns on and lights LED1. (Note: the 0.6V drop across Q1's base/emitter is ignored here because ZD1 conducts before its rated voltage due to the very low current involved). Why choose 4.7V below the power rail as the turn-on point? The reason is that, due to the drive limitations and the nature of emitter followers, they can be expected to have at least 4V across them when they saturate (ie, clip). ZD1 can be increased to a 5V or 6.2V type if the circuit is to be used with a monster amplifier.

The value of R3 should be customized according to the amplifier's supply rail, so that LED1 operates with the correct brightness. To do that, first measure the amplifier's positive supply voltage, then use Ohms Law (R = V/I) to calculate the value of R3 for a current of about 20mA. As it stands, this circuit can only be used to monitor the positive-going half-cycles of the audio waveform. If you want to monitor the negative half-cycles as well, you will have to build a second circuit with the following changes: (1) reverse both LED1 and ZD1; and (2) use BD139 (NPN) transistors for Q1 & Q2. Note that, in both cases, you should use the earth inside the amplifier, as the speaker negative may not be earth (such as in a bridged output).

Author: Philip Chugg - Copyright: Silicon Chip Electronics Magazine

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Audio Pre-Amplifier

Simple Audio Pre-Amplifier

This simple circuit provides good gain to too audio singnals . Use it in main of an RF oscillators to make an RF transmitter that is very sensitive to sound

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Alternating ON-OFF Control

Use this circuit instead of a standard on-off switch. Switching is very gentle. Connect unused input pins to an appropriate logic level. Unused output pins *MUST* be left open!. First 'push' switches ON,
another 'push' switches OFF. You can use 1/4 watt resistors if they are metal-film type. Any proper
substitute will work for Q1, including the european TUN's. For C2, if you find the relay acts not fast

enough, leave it out or change to a ceramic cap between 10 and 100nF.

Parts List
All resistors are 1/2 Watt and 5% tolerance.
R1 = 10K
R2 = 100K
R3 = 10K
C1 = 0.1µF, Ceramic
C2 = 1µF/16V, Electrolytic
D1= 1N4001
Q1 = 2N4401 (ECG123AP, NTE123AP, etc.)
IC1 = 4069, CMOS, Hex Inverter (14069), or equivalent
S1 = Momentary on-switch

Copyright © Tony van Roon

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Simple Electronic Lock

Simple Electronic Lock Circuit diagram. There are six (or more) push switches. To 'unlock' you must press all the correct ones at the same time, but not press any of the cancel switches. Pressing just one cancel switch will prevent the circuit unlocking. When the circuit unlocks it actually just turns on an LED for about one second, but it is intended to be adapted to turn on a relay which could be used to switch on another circuit. Please Note: This circuit just turns on an LED for about one second when the correct switches are pressed. It does not actually lock or unlock anything!

Simple Electronic Lock Circuit diagram :

Simple Electronic Lock Circuit Diagram

Stripboard Layout :

Parts :

• resistors: 470, 100k ×2, 1M
• capacitors: 0.1μF, 1μF 16V radial
• on/off switch
• push-switch ×6 (or more)
• stripboard 12 rows × 25 holes
• red LED
• 555 timer IC
• 8-pin DIL socket for IC
• battery clip for 9V PP3
•  

A kit for this project is available from RSH Electronics: www.kpsec.freeuk.com

Copyright :John Hewes 2006,  The Electronics Club

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Smart Receptionist With Smartlock System

Presented here is a security system that lets you see a visitor while EFY Tested your main office door is locked. If you are in the middle of a meeting in a conference room and there is a visitor at the door, this system will send a notification to your smartphone with a photo of the visitor as email. If you approve, you either use your mobile or PC to unlock the front door using a Web browser. Alternatively, if you have a door bell with intercom facility, you can talk to the visitor when he or she rings the door bell.

A typical block diagram of the smart receptionist with a smartlock system is shown in Fig. 1.

 Fig. 1: Smart receptionist with a smartlock system

Circuit and working

Interfacing circuitry of the smart receptionist and lock system is shown in Fig. 2. Raspberry Pi runs on standard Raspbian Linux distribution with Wi-Fi dongle, GPIO library and software written in Python language. Raspberry Pi GPIO4, GPIO17 and GPIO25 are connected with resistors R3, R2 and R1, respectively, to make logic level low.

Door bell.

The door bell signal from CON3 is routed to GPIO17 pin on Raspberry Pi. When a visitor rings the door bell, the status LED glows and GPIO17 becomes high. Amplitude of the door bell signal output depends on the door bell/chime used. You can use a door bell that gives 3V signal.

 Fig. 2: Circuit diagram of the smart receptionist with a smartlock system

Captured signal should not exceed Raspberry Pi’s 3.3V limit on GPIO pins. So a 3V zener (ZD1) is used in this circuit. Ground wire of the door bell circuitry should be connected to GND pin of Raspberry Pi and the anode of status LED to GPIO17. 
                                                                                                                                   
When GPIO17 becomes high, the system captures the photo of the visitor through the webcam connected to Raspberby Pi through USB. Captured photo is sent to your email ID configured in your source program.

Open the attachment in your email and check the photo of the visitor. After your visitor is identified, either open the door directly or talk to him or her through an intercom if it is installed at the door.
Smartlock.

When status LED glows to indicate that the door bell is ringing, press Camera tab on your Web browser (Fig. 3). This will make GPIO25 pin of Raspberry Pi high, enabling the webcam to capture the photo of the visitor. Captured photo is sent to your email ID.

After your visitor is identified, you may open the door by pressing Lock tab on the Web browser. With Lock tab pressed, GPIO4 becomes high. Since relay driver transistor T2 is connected to GPIO4, T2 conducts and energises relay (RL1). This provides a 12V DC supply from CON2 to the solenoid lock connected at CON1, and the door opens.

Sourced By: EFY : Author:  Biswajit Das was manager - R&D, EFY Labs till recently

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IoT Based Notification System Using Android App

Presented here is a smart notification system for a door sensor, motion detector, fire alarm and doorbell using Raspberry Pi (RPi) and Pushover app. The project triggers an event through various sensors and sends notifications to your smartphone. Sensors used in this project include a magnetic reed switch for a door or window, PIR sensor for motion detection and NTC thermistor for fire alarm.

The issue of security is becoming more prevalent. The Internet of Things (IoT)-enabled home security solutions like this use sensors to collect and share data from multiple edge devices. If an attacker gains access to these smart systems through malicious means, the underlying functional logic of control systems can alert the owner. Connected home security systems offer a myriad of features including door and window sensors, motion detectors, fire alarms and so on, all connected via the Cloud to a mobile device or the Web.

Block diagram of the smart alert notification system using Android app is shown in Fig. 1.

Pushover app

Pushover is a service on the Web and an app for your phone or tablet that acts as a gateway for notifications. It can alert you to anything, including job postings, status of rain, emails from important people or a sensor activated in your home. Pushover lets you set up as many noise-free time periods as you like, using a feature called Quiet Hours. You can access alarm indications from anywhere in the world.
Circuit and working

Circuit diagram of the smart notification system using RPi is shown in Fig. 2. Hardware includes Raspberry Pi, Android phone, PIR sensor, reed switch, NTC thermistor, doorbell and a few other components.

Fig. 2: Circuit of the IoT based notification system using RPi

The PIR sensor connected across CON1 detects the presence of people through changes in infrared radiation from the human body in front of the door. It outputs around 3.3V high signal whenever it detects radiation change and correspondingly sends alert signals to your Android phone.

The magnetic reed switch connected across CON2 is usually installed on the frame of an exterior door or window. When the door or window opens, it moves away from the frame, magnetic field around the switch gets removed and corresponding alert signal is sent to your Android phone.

NTC thermistor connected across CON3 is used as the temperature-cum-fire sensor. Resistance of the NTC thermistor decreases with increase in temperature.

At room temperature, transistor T2 conducts. When temperature of the sensor goes above 70°C [depending on thermistor constant (K)], T2 stops conducting. When T2 stops conducting, an alert signal is generated in RPi, which is sent as a push message to the Android phone.

Most doorbells produce pulse-wave modulation waves while ringing. You need to hack the doorbell so that it produces at least 2V (pulse-wave modulation with low-pass filter) output signal. You may use this signal as an interrupt signal to drive RPi pin and generate an alarm log in your Android phone. Door-bell signal is fed to RPi through CON4.

When someone rings the doorbell, you will get a notification on your phone. Various alert notifications received on Android smartphone are shown in Fig. 3.

Software

Pushover makes it easy to get real-time notifications on your smartphone. Follow the steps given below to activate Pushover app on your Android device.

1. On your mobile device, open Pushover app and log into your account. You will be asked to register your device by providing a name for it.
 2. Visit https://pushover.net on your computer and log into your account. You should see your devices listed in a section called Your Devices, a little way down the page. Verify that the devices you have registered are on this list and are enabled.

3. Note down your user key (like, uyaa3u82r6rw853a2zhwj7afyxq4ba) as shown in Fig. 4. You will need it for your Python code.

Fig. 4: Typical user key generated on Pushover app

4. To get API key, click on Your Applications (doorbell) and note down your API token/key (like, au3kybdp4bmv3xs3qp1prku7pcrp9r) as shown in Fig. 5.

Fig. 5: Typical API key

5. Under Settings in Pushover, you can set an audio alert for quiet hours, etc for your mobile as per your requirement.

Testing Pushover app

Open Pushover app on your Android mobile. Open appliance.py file on the terminal in RPi. Change user_key and application_key in the code with your keys obtained as shown in Figs 3 and 4. Run the following command:

$ sudo python appliance.py

With the server connected to RPi, you will get ‘Appliance Server Started’ message in the terminal and ‘Appliance Started’ message on your mobile. As per the interrupt signal received from the input sensors (motion, door break, fire, doorbell, etc), the corresponding alert notification will be received on your Android phone through Pushover app.

Download Source code

Sourced By : EFY Author

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Simple Bio-Feedback Circuit Diagram

Feed-back, means a reaction to a stimulus, I will explain, the concept is simple, but explanation is a bit troubled, bio-feedback is to electronically feed back a user through sound or Visual, it is possible to control your meditation state, causing the user to reach a pre-established state at any time.

Simple Bio-Feedback Circuit Diagram

With this circuit it is possible to feedback from consciously varying the resistance of the skin, even though the equipment helps, even so will require training for this.

In order to use the biofeedback, the user must remain at rest, preferably lying down, since physical activity and variations of the emotional state influence the resistance of the skin, regardless of our will or unconsciously.

The biofeedback electrodes should be attached to the ring finger and index finger by tape or tape, and the hand should be in a comfortable, stationary position.

How Bio-Feedback Works

The biofeedback has as its main component an integrated circuit 555, configured as an astable multivibrator. The oscillation frequency of the 555 depends directly on the values of C1 and the collector current of Q1, which is connected as a current generator.

The resistors R1 and R2 attached to its base form a resistive divider which together with R3 and R9 determine the collector current of the transistor.

When the person connects the electrodes, the skin resistance is placed in parallel with R2, which changes the frequency of the oscillator. If skin resistance increases or decreases, we will see a drop or increase in the oscillation frequency of Cl1. R8 functions as volume control for Q3, which is the power amplifier.

Relation of Bio-Feedback Components

R1 – 47 kOhm x 1/4 Watt
R2 – 680 kOhm x 1/4 Watt
R3, R4, R6 – 1 kOhm x1/4 Watt
R5 – 22 kOhm x 1/4 Watt
R7 – 10 kOhm x 1/4 Watt
R8 – 50 kOhm – potentiometer linear
R9 – 10 kOhm – trimpot
C1 – 100 ηF pollster
C2 – 10 ηF pollster
CI1 – NE 555 ou equivalent
Q1 – BC 178 ou equivalent
Q2 – BC 549 ou equivalent
Q3 – 2N3055 ou equivalent

The biofeedback power is provided by a 9 Volt battery, but a well filtered source to avoid noise can be used without problems.

Source New Electronic Magazine 1 of 1977 - author of Gary Gronich.

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Dual-Channel Active AC Analogue Probe Circuit Diagram

 This is a Dual-Channel Active AC Analogue Probe Circuit Diagram. It is suitable for oscilloscopes, multimeters and other analogue measurement equipment.

When experimenting with AM receivers for long, medium and short waves, users need a high-impedance analogue probe with input capacitance below 20pF. The required input impedance from the probe at low frequency is usually one mega-ohm or above.

Most of the low-cost passive probes for oscilloscopes have input capacitance well above 100pF. If you include the input capacitance of the oscilloscope, the total capacitance becomes even higher. The bandwidths of these low-cost passive probes are usually limited to 1-2MHz. These cannot be connected in parallel with L-C networks in AM receivers because that will change the parameters of these networks significantly.

Circuit and working

Fig. 1 shows the circuit diagram of the dual-channel, active AC analogue probe. It is built around two n-channel PN4393 JFET transistors (T1 and T2) and a few resistors and capacitors.

Dual-Channel Active AC Analogue Probe Circuit Diagram

Most of the oscilloscopes come with two channels, so you need a dual-channel active probe with common ground and common power supply.

At low frequency, the input resistance of the probe, determined mainly by resistors R3 and R4, is around 10-mega-ohm. At high frequency, the input impedance is determined by the total input capacitance of the probe. With careful implementation and use of appropriate JFETs, you can obtain input capacitance below 20pF.

Transistors T1 and T2 should have low noise level and low input capacitance. So you can choose from transistors like PN4391, PN4392 and PN4393 as these have input capacitance of typically 14pF. You can also use transistors J201, J202, J203, 2N5457, 2N5458 and BF245 (with 1.5dB noise figure). High-frequency JFETs in small cases are preferred but these are costly.

The voltage between the drain and the source of T1 and T2 is adjusted to around half of the power supply, using resistors R6 through R9 and jumpers J3 and J4. The circuitry using resistor R5, presets VR1 and VR2, and capacitor C3 is used to adjust the offset voltage applied to the gates of the JFETs. These components are not mandatory. If you choose not to use these, close jumpers J1 and J2, and connect resistors R3 and R4 to ground.

The gain of each of the channels is slightly below unity, but that is not important in most of the cases. Most oscilloscopes produce a square wave reference signal, which can be used for measurement of the gain and evaluation of the probe.

Construction and testing

An actual-size PCB layout for dual-channel active AC analogue probe is shown in Fig. 2 and its components layout in Fig. 3. After assembling the circuit on the PCB, enclose it in a suitable cabinet with connectors CON1 and CON2 affixed on the front side and connectors CON3 and CON4 on the rear side of the cabinet.

 Actual-size PCB layout of dual-channel active AC analogue probe

 Components layout for the PCB

The probe can be implemented on a small PCB. During testing and adjustment, the inputs of the probe can be connected or soldered to L-C networks using very short (3-4cm long) conductors.

Power the circuit using a dry battery or rechargeable battery. The circuit does not require any special adjustment, so you can start using it straightaway after assembly. If you use jumpers J3 and J4, adjust VR1 and VR2 for the best performance of the probe.

After proper implementation, the probe can have bandwidths above 10MHz with a signal generator having low output impedance.

Sourced By :  EFY : Author Name : Petre Tzv Petrov

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