LED Volt Meter Circuit

Here is a Simple LED Volt meter to Monitor the charge level in Lead Acid Battery or Tubular battery. The terminal voltage of the battery is indicated through a four level LED indicators. The nominal terminal voltage of a Lead Acid battery is 13.8 volts and that of a Tubular battery is 14.8 volts when fully charged. 

 LED Volt Meter Circuit Diagram

The LED voltmeter uses four Zener diodes to light the LEDs at the precise breakdown voltage of the Zener diodes. Usually the Zener diode requires 1.6 volts in excess than its prescribed value to reach the breakdown threshold level. When the battery holds 13.6 volts or more, all the Zener breakdown and all LEDs light up. When the battery is discharged below 10.6 volts, all the LEDs remain dark. So depending on the terminal voltage of the battery, LEDs light up one by one or turns off.

Author: D. Mohan Kumar Copyright: electroschematics.com

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Sensitive Audio Power Meter

As a follow-up to the simple audio power  meter described in [1], the author has developed a more sensitive version. In practice,  you  rarely  use  more  than  1 watt  of  audio  power in a normal living-room environment.  The only time most people use more is at a  party when they want to show how loud their  stereo system is, in which case peaks of more  than 10 W are not uncommon. With this circuit, the dual LED starts to light up  green at around 0.1 watt into 8 ohms (0.2 watt  into 4 ohms). Naturally, this depends on the  specific type of LED that is used.

 
Circuit diagram:

 

Sensitive Audio Power Meter Circuit Diagram

 

Here it is  essential to use a low current type. The capacitor is first charged via D1 and then discharged via the green LED. This voltage-doubler effect  increases the sensitivity of the circuit. Above a level of 1 watt, the transistor limits the current through the green LED and the red LED con ducts enough to produce an orange hue.The red colour predominates above 5 watts. Of course, you can also use two separate ‘normal’ LEDs. However, this arrangement cannot generate an orange hue. For any testing that may be necessary, you should use  generator with a DC-coupled output. If there is a capacitor in the output path, it can cause misleading results.

Reference: Simple Audio Power Meter, Elektor July & August 2008.

Author : Michiel Ter Burg - Copyright : Elektor Electronic

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Linear RF Power Meter Circuit

The National Semiconductor LMV225 is a linear RF power meter IC in an SMD package. It can be used over the frequency range of 450 MHz to 2000 MHz and requires only four external components. The input coupling capacitor isolates the DC voltage of the IC from the input signal. The 10-k? resistor enables or disables the IC according to the DC voltage present at the input pin. If it is higher than 1.8 V, the detector is enabled and draws a current of around 5–8 mA. If the voltage on pin A1 is less than 0.8 V, the IC enters the shutdown mode and draws a current of only a few microampères. The LMV225 can be switched between the active and shutdown states using a logic-level signal if the signal is connected to the signal via the 10-kR resistor.

Circuit diagram:

 Linear RF Power Meter Circuit Diagram

The supply voltage, which can lie between +2.7 V und +5.5 V, is filtered by a 100nF capacitor that diverts residual RF signals to ground. Finally, there is an output capacitor that forms a low-pass filter in combination with the internal circuitry of the LMV225. If this capacitor has a value of 1 nF, the corner frequency of this low-pass filter is approximately 8 kHz. The corner frequency can be calculated using the formula fc = 1 ÷ (2 p COUT Ro) where Ro is the internal output impedance (19.8 k?). The output low-pass filter determines which AM modulation components are passed by the detector.

The output, which has a relatively high impedance, provides an output voltage that is proportional to the signal power, with a slope of 40 mV/dB. The output is 2.0 V at 9 dBm and 0.4 V at –40 dBm. A level of 0 dBm corresponds to a power of 1 mW in 50 R. For a sinusoidal wave-form, this is equivalent to an effective voltage of 224 mV. For modulated signals, the relationship between power and voltage is generally different. The table shows several examples of power levels and voltages for sinusoidal signals. The input impedance of the LMV225 detector is around 50 R to provide a good match to the characteristic impedance commonly used in RF circuits.


The data sheet for the LMV225 shows how the 40-dB measurement range can be shifted to a higher power level using a series input resistor. The LMV225 was originally designed for use in mobile telephones, so it comes in a tiny SMD package with dimensions of only around 1 × 1 mm with four solder bumps (similar to a ball-grid array package). The connections are labelled A1, A2, B1 and B1, like the elements of a matrix. The corner next to A1 is bevelled.

Author: Gregor Kleine Copyright: Elektor Electronics

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Simple Simulated inductor Circuit Diagram

This is the Simple Simulated inductor Circuit Diagram. In the this circuit With a constant current excitation, the voltage dropped across an inductance in-(in creases with frequency. Thus, an active device whose output increases with frequency can be characterized as an inductance. 

 Simple Simulated inductor Circuit Diagram

The circuit yields such a response with the effective inductance being equal to: L = R1R2C. The Q of this inductance depends upon Rl being equal to R2. At the same time, however, the positive and negative feedback paths of the amplifier are equal leading to the distinct possibility of instability at high frequencies. Rl should, therefore, always be slightly smaller than R2 to assure stable operation.

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Build a Curve Tracer Circuit Diagram

How to Build a Curve Tracer Circuit Diagram ? This is the simple Curve Tracer Circuit Diagram. This circuit Useful for checking diodes, transistors, triacs, SCRs, resistors, and LEDs, this curve tracer should prove useful in the experimenter`s lab. 

 Curve Tracer Circuit Diagram

It displays the volt-ampere characteristic of a two-ter-minal device on an oscilloscope. This is a simple block diagram of the EZ-Curve. Current-limited AC signals are passed through both the device under test and a precision resistor to yield current and voltage readings.

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Simple Panel Frequency Meter Circuit Diagram

This is a Simple Panel Frequency Meter Circuit Diagram to measure the frequency of 230V AC mains. When you connect it to the 230V AC line, the display shows the line frequency. Generally, the line frequency is 50 Hz, which may vary from 48 Hz to 52 Hz. Beyond this frequency range, sensitive equipment may start malfunctioning.

The AC mains supply is stepped down by transformer X1 to deliver a secondary output of 9V-0-9V AC, 250 mA. The secondary output of the transformer is rectified by diodes D1 and D2, filtered by capacitor C1 and given to regulator IC1 to produce regulated 6V DC. 9V AC is also connected to pins 2 and 6 of IC2 via resistor R1. Timer IC2 converts the sinewave frequency sample of AC mains into a square wave that is more suitable for the circuit operation.

Simple Panel Frequency Meter Circuit Diagram

Fig. 1: The circuit of the panel frequency meter

IC CD4093 (IC3) is used as an oscillator-cum-divider. The oscillator, wired around gate N1, produces 10Hz clock. Decade counter IC4 divides 10Hz clock by 10 to produce 1Hz clock. The output of gate N1 is fed back to its inputs via potentiometer VR1 and resistor R4. Capacitor C2 connected between the inputs of gate N1 and ground charges/discharges depending on the logic level at the output of gate N1. The values of VR1, R4 and C2 are selected to produce accurate 10Hz clock.

Decade counter IC CD4017 (IC4) divides the output of IC3 by 10 to provide one pulse per second. LED1 connected to pin 12 of IC4 gives one flash per second to indicate that the oscillator and the counter are working properly.

 Fig. 2: Top and bottom views of LTS543 common-cathode, 7-segment displays

This 1Hz clock is fed to clock pin 14 of decade counter IC CD4017 (IC5), whose Q0 output is given to pin 2 and the square wave produced by IC2 is given to pin 1 of AND gate N1. Therefore, the unknown frequency of AC mains line, applied to pin 1 of AND gate N1, passes through it for only one second and the number of clocks per second are counted by IC7 and IC8.

Decade counters/7-segment decoders IC7 and IC8 are cascaded to drive common-cathode, 7-segment displays DIS1 and DIS2 (each LTS543). DIS1 shows units place of the frequency and DIS2 shows tens place. The top and bottom views of LTS543 common-cathode, 7-segment displays are shown in Fig. 2.

This is an auto-reset circuit. You can select the reset time of 1 second through 5 seconds using rotary switch S2, which is connected to reset pins of IC5, IC7 and IC8. For long-time display of the frequency, keep the knob of rotary switch S2 towards fifth position. Keeping rotary switch S2 to first position (minimum reset time) allows you to instantly see any variation in the supply frequency on the display. Also, while adjusting the generator frequency to mains frequency, keep rotary switch S2 towards first position.

Author:  V. David Sourced By: EFY

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Simple Stereo VU Meter

I like to see lights move to music. This project will indicate the volume level of the audio going to your speakers by lighting up LEDS. The LEDS can be any color so mix them up and really make it look good. The input of the circuit is connected to the speaker output of your audio amplifier. You want to build two identical units to indicate both right and left channels. The input signal level is adjusted by the 10k ohm VR. If you wish to make a very large scale model of this unit and hang it on your wall there is an optional output transistor that can drive many LEDS at once. The unit I built drove three LEDS for each output. The sequence of the LEDS lighting are as follows Pin 1, 18, 17, 16, 15, 14, 13, 12, 11, 10.

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Check Inductors With This Simple Q Meter

While LCR meters are readily available at reasonable cost, they do not measure the Q of an inductor. This circuit enables you to measure the Q of inductors with the aid of an RF signal generator. A capacitor is connected in parallel with the inductor to form a tuned circuit. By varying the frequency, you can measure the resonance frequency of the tuned circuit and its -3dB bandwidth. The Q is then the resonance frequency divided by the -3dB bandwidth. Transistor Q1 is an emitter follower acting as input buffer to drive RF transformer T1. The secondary winding of T1 then drives the parallel tuned circuit formed by the inductor under test (Lx), T1’s secondary and tuning capacitor VC.

The tuned circuit so formed is buffered by JFET Q2 and transistor Q3 which form a cascode stage with about 3dB of gain. The JFET provides a high impedance so that the loading of the tuned circuit is minimal (note: an MPF102 can be substituted if you cannot obtain a 2N5485). The RF output from Q2's collector can be monitored by an oscilloscope to easily find the point of resonance and read the frequency. Alternatively, the RF output can be read by an external frequency meter. Diodes D1 & D2 and the 5.6nF capacitors form a voltage doubler rectifier to drive a 100µA DC meter so that the resonance can be found (in the absence of an oscilloscope).


Trimpot VR1 provides a sensitivity adjustment for the meter. Transformer T1 is wound on a 12mm diameter ferrite toroid core. The primary winding consists of 50 turns of 0.2mm diameter enamelled copper wire, while the secondary is a single turn consisting of a strip of brass 0.5mm thick and 2.5mm wide bent into a horseshoe shape and threaded through the centre of the toroid. VC is a small AM tuning capacitor with both gangs connected in parallel.

To measure Q, the output of the RF signal generator should be around 0.5V peak. Adjust the frequency until the meter's reading peaks, then adjust VR1 so that the meter reads full scale (100µA). Read the resonance frequency F0 from the frequency scale of the signal generator or better still, the reading on a frequency meter.

Next, increase the signal frequency until the meter reads 70µA and note this frequency as F2. That done, reduce the frequency on the signal generator below the resonance frequency until the meter again reads 70µA and note this frequency as F1. The Q can now be calculated as:

Q = F0/(F2 - F1)

While using a variable tuning capacitor will enable a wider range of inductors to be tested, the main advantage is estimating the distributed capacitance of the inductor as well. To do this, you have to calibrate the tuning scale with a capacitance meter, by measuring the capacitance across the tuning capacitor with no inductor connected. This is done with the unit switched off. Marking off increments of 20pF should be sufficient.

Set the tuning capacitor to say ¼ of its maximum value and note this value as C1. Adjust the RF signal generator frequency so that the inductor under test is at resonance and note this frequency as F0. Now set the RF generator frequency to half F0, adjust the tuning capacitor until resonance and note this capacitance as C2. The distributed capacitance of the inductor is (C2 - 4C1)/3.

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