Lavalier Microphone Tester Circuit

Thread Starter


Joined Feb 8, 2022
Hello guys! I'm trying to build a small circuit that can detect a faulty microphone or an intermittent microphone. It is meant to be used with lavalier microphone.
So I asked chat GPT for ideas (yes aha) and it came up with this. Does it make any sense? I tried to put it quickly on a breadboard but it doesn't seem to work at all...
Have better ideas?


This circuit uses an LM358 dual operational amplifier to create an oscillator that produces an audio tone. The microphone's signal is compared to this tone, and if the microphone is functioning correctly, a green LED lights up. If a fault is detected, such as cable intermittence or a non-working microphone, a red LED lights up.

Parts List:
  • LM358 Dual Operational Amplifier
  • 2N3904 NPN Transistor
  • Green LED (Pass Indicator)
  • Red LED (Fail Indicator)
  • Resistors:
    • R1: 1k Ohm
    • R2: 10k Ohm
    • R3: 10k Ohm
    • R4: 1k Ohm (for Green LED)
    • R5: 1k Ohm (for Red LED)
  • Capacitor:
    • C1: 1uF
  • On/Off Switch (SW1)
  • Microphone (3.5mm)
  • 3V Rechargeable Battery
  • Breadboard or PCB for prototyping
  • Jumper wires
Circuit Functionality:
  • Power Section:
    • Toggle the On/Off switch (SW1) to power the circuit with a 3V rechargeable battery.
  • Oscillator Section:
    • The LM358 generates an audio tone oscillator with resistors R1, R2, R3, and capacitor C1.
    • The tone is compared with the microphone's signal.
  • Microphone Section:
    • The microphone is connected to the circuit.
    • The microphone's signal is fed into the LM358.
  • Indicator LEDs Section:
    • If the microphone is working, the green LED lights up.
    • If a fault is detected (such as no signal or intermittence), the red LED lights up.
  1. Turn on the circuit using the On/Off switch.
  2. Plug the lavalier microphone into the 3.5mm jack.
  3. The green LED lights up if the microphone is functioning properly.
  4. The red LED lights up if a fault is detected (cable intermittence or non-working microphone).
  5. Toggle the On/Off switch to power off the circuit when testing is complete.
  • The circuit does not require external sound input.
  • The green LED indicates a functioning microphone, while the red LED indicates a fault.
  • Customize resistor values as needed for specific LED brightness.
  • Build the circuit on a breadboard or PCB for testing and troubleshooting.



Joined Nov 6, 2012
Why not just make a Head-Phone-Amplifier with a lot of built-in Gain ?

This will also indicate excessive distortion, or other unwanted Noises.

Your Ears are much more sensitive than a sketchy LED-Circuit.

I still can't figure-out why You would want to test a Microphone,
generally they either work, or they don't.

Thread Starter


Joined Feb 8, 2022
LowQ, I understand your thinking. I working as sound recordist on film and television. I want to create a portable device to test body worn microphone in a simple connection. Either to test microphones away from a sound cart on a film set, or to test a batch of mics at the beginning of the day or the end of the day, it would be a very useful thing to have.
Yes my ears are better than a - for now- sketchy LED circuit, but when testing an RF body worn microphone you can hear RF drops or interference, clothing rustle, cable noise etc... It's meant to test if there is a short somewhere in the mic cable or connector, which happens a lot.


Joined Jan 23, 2018
Generally the test of a microphone must show not only that it is functional and does not produce noise, but also, very important, the check must verify that the connection s do not vary with motions of the microphone cord. That is the primary failure mode of microphones that have an attached cord. I do not see that the circuit shown provides that option. It can verify basic operation, but that is only part of the requirement to verify correct operation.

A complete verification will include both the ability to listen to the output and measure the amplitude..
So the tester must at least provide an undistorted audio output from a low-noise, low distortion transducer. For quantitative measurements in also needs to provide a known acoustic signal to the microphone and a display of the signal amplitude. Then the no-signal output can be used to verify that there is no noise created by the microphone itself.


Joined Jan 23, 2018
Thw WIRING DIAGRAM in post #1 appears to mostly verify that the microphone is drawing the correct amount of current. So I am not sure how it will perform checking a plain dynamic microphone. I did not examine the circuit for that capability.
And I would not trust any source that does not explain just what it is that the sensor is checking and what the accept limits are. THOSE are important. A small amplifier built into a headphone could give you both a signal to hear and also an indication that the current draw was within limits, as well as warn of any opens or shorts. And it could run on a single 9 volt battery for weeks.

Audioguru again

Joined Oct 21, 2019
The microphone type is not mentioned, It might be dynamic, electret or piezo and they all need a different preamp circuit.

The preamp circuit you attached has many serious errors and will not work. There is no oscillator and the LM358 dual opamp is never powered.


Joined Jan 23, 2018
In addition, the RED LED will not light, it is backwards, and, as AG states, there does not seem to be any oscillator ability.
So the circuit designers are safe from the version of chat that you used. The WIRING DIAGRAM is incomplete and quite poorly thought out.
Also, what sort of electronic functional test can be done by applying a signal to a microphone?? IT would produce an audio tone from an unamplified dynamic or crystal mic, but nothing from an eletret mic or an amplified dynamic mic.
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