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This is a simple audio Milli volt meter circuit diagram . This Audio Milli Volt Meter Circuit has a flat response from 8Hz to 50 kHz at -3 db on tbe 10-mV range. The upper limit remains the same on tbe less sensitive ranges, but the lower frequency limit covers under 1 Hz. Simple Audio Milli Volt Meter Circuit Diagram

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 thr...

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 collec...

If you, like so many other people in this day and age, arrive home from work stressed out and with the problems of the day still lingering,this simple little instrument will go a long way to relieving nervous tension. Of the various types of feedback devices, probably the best approach for the amateur experimenter is the Galvanograph, better known as the Galvanic Skin Response Monitor. The instrument described here relies for its operation on changes in skin resistance in sympathy with changes in emotional state. An increase in tension level reduces skin resistance and, conversely, a decrease in tension is accompanied by an increase in skin resistance. The correlation between emotional stress and skin resistance is still not fully understood. What is known, though, is that minute changes in the permeability of the skin produce corresponding voltage variations across two electrode pads attached to two fingers on the same hand. Tension Monitor meter circuit These signal fluctuations are ...

Weston (M.I) Type Frequency Meter Principle:  It is a moving iron instrument which operates on the principle of variation of impedance in an inductive circuit with variation of frequency. Weston Frequency Meter Construction: It consists of two coils A and B mounted perpendicular to each other. Each coil is divided into two sections. The connections are as shown in the above fig. The branch of coil has a resistance R 1 connected in the series with it while coil B has a reactance coil L 2 in series with it. Circuit of coil A is in parallel with a reactance coil L 1 while that coil B is in parallel with a resistance R 2 . The moving element is a soft iron needle. The needle is pivoted on a spindle which is also carries a pointer and damping vanes. There is no controlling torque. The series reactance L 0 acts to suppress higher harmonics in the current of instrument and therefore tends to minimize the waveform errors in its indication. Working: When the meter is connected across th...

Build a simple audio Milli volt meter circuit diagram . This Audio Milli Volt Meter Circuit has a flat response from 8Hz to 50 kHz at -3 db on tbe 10-mV range. The upper limit remains the same on tbe less sensitive ranges, but the lower frequency limit covers under 1 Hz. Simple Audio Milli Volt Meter Circuit Diagram Sourced By : http://circuitsdiagram-lab.blogspot.com/2013/11/simple-audio-milli-volt-meter-circuit.html

A simple field strength meter circuit is presented in this article, let's learn more about it's construction details. For a radio receiver, it is often a pain to evaluate the strength of the field on which the performance of the radio is dependent. The circuit used for this purpose is a cost effective yet useful tool to achieve performance evaluation of the radio field strength. The extreme left of the circuit is the crystal receiver or crystal radio part of the circuit. A suitable germanium diode like the IN34 or AA119 is recommended. A silicon diode does not achieve the performance of a germanium diode for its functions as a varactor because of its depletion layer characteristic. The inductance can be built by 6 to 8 turns of enameled wire having a diameter of 1milimeter and a coil diameter of millimeter. The capacitor selected is around 100picoFarrad that resonate with inductance. By adjusting the spacing of the turns, the frequency can be varied. The secon...

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 co...

As electrolytic capacitors age, their internal resistance, also known as "equivalent series resistance" (ESR), gradually increases. This can eventually lead to equipment failure. Using this design, you can measure the ESR of suspect capacitors as well as other small resistances. Basically, the circuit generates a low-voltage 100kHz test signal, which is applied to the capacitor via a pair of probes. An op amp then amplifies the voltage dropped across the capacitor’s series resistance and this can be displayed on a standard multimeter. In more detail, inverter IC1d is configured as a 200kHz oscillator. Its output drives a 4027 J-K flipflop, which divides the oscillator signal in half to ensure an equal mark/space ratio. Two elements of a 4066 quad bilateral switch (IC3c & IC3d) are alternately switched on by the complementary outputs of the J-K flipflop. One switch input (pin 11) is connected to +5V, whereas the other (pin 8) is connected to -5V. The outputs (pins 9 & ...

Normally we often encountered the frequency meter can be used in speed sensor, tachometer, measurement or signal recurring. This frequency to voltage converter (FVC) can be used to change the voltage into a digital or analog tachometer. Circuit that consists of three blocks. The first block is squarer, the input signal to a square wave. This block is protected from high input voltage up to 400V, but remember this only works if the value of capacitor C1 is for 400V. Input Impedance around 560k, so it is safe to connect the ignition pick-up coil in parallel with the CDI (capacitor discharge ignition) circuits without a problem. Supply is protected from voltage spike by Zener diode D3. Here is a schematic picture: The second block is retriggerable monostable multi vibrator. Monostable multi-vibrator is to convert fixed width pulses to provide output, the voltage output of the average will depend on the duty factor pulses input / waveform, but only depends on the input frequency. Pulse wid...

The water-tank level meter de-scribed here is very simple and useful for monitoring the water level in an overhead tank (OHT). The water level at 30cm intervals is monitored and continuously indicated by LEDs ar-ranged in a meter-format. When all the LEDs are ‘off’, it indicates that the OHT is empty. When the water level reaches the top limit, the whole LED-meter begins to flash. The height at which the level-sensing electrodes are fitted is adjustable. Thus, the minimum and maximum level settings may be varied as desired. The range of the meter can also be enlarged to cater to any level. No special or critical components are used. CMOS ICs are used to limit the idle current to a minimum level. Even when all the LEDs are ‘on’, i.e. water reaches the top level, the demand on the power supply is reasonably low. Further, the extremely high input resistance of the Schmitt inverter gates reduces the input current and thus minimises the erosion of electrodes. The princi-pal part of the dev...

Remote Field Strength Meter Circuit Diagram. This field strength meter consists of a tuned crystal detector producing a dc output voltage from a transmitted signal. The dc voltage is used to shift the frequency of a transmitter of 100-mW power operating at 1650 kHz. The frequency shift is proportional to the received field strength. This unit has a range of several hundred feet and is operated under FCC part 15 rules (100-mW max power into a 2-m-iong antenna between 510 and 1705 kHz). Remote Field Strength Meter Circuit Diagram