SensingBench electronicsUnplug and unscrew

Electret microphone

Also called mic capsule, condenser mic.

The little can in headsets, webcams, cameras, and old phones. Two pads, needs a bias resistor to a quiet supply (typically 2–5 V through 2.2 kΩ). It is not a speaker and it is not a MEMS mic on a flex, though those are also worth keeping as a module.

If you are new to this category

A sensor reports a condition such as weight, light, temperature, or position. Many sensors do not switch fully on or off. A kitchen scale bar, for example, changes by thousandths of a volt. Keep the small board that read the sensor if you still have it.

Keep the connector. Write down the wire colors before you cut them. If you do not know which wire is which, the sensor is hard to reuse.

Four wires on a scale sensor

Red and black feed the sensor a steady few volts. Green and white are the tiny signal, measured between them, not from either one to ground. Pressing the bar changes that signal by millivolts. A normal meter on DC volts can show that it responds. Turning it into a number on a screen wants a small amplifier board, often an HX711.

Specification. The right-hand column is what is typical. The label on the part in your hand wins if they disagree.
What to look for	Usual figure
Polarity	The pad connected to the case is usually ground
Signal	Millivolts. It wants an amplifier. A GPIO pin will not hear it.

Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.

What people actually use it for

A sound trigger
A voice input with a preamp
Replacing a dead headset mic

Leave this one when

The diaphragm is dented. They do not un-dent.

Buying a new one is the better idea when

A module that already has the bias and an amplifier, if you do not want to build the front end.

How to tell if this one still works

Bias it and look at the output on a scope, or feed a mic input. Tap the case. You should see the tap.

Tools you will want: Resistor, Scope or a mic input.

Words on this page

Short meanings, so the rest of the entry is readable if you are not already doing this every weekend.

polarity: Which side is plus and which is minus. Reversed polarity ruins a lot of electronics. The symbol on a power brick is the map.
diaphragm: A flexible disc that moves with pressure or with a pump. In a washer it is how a small switch senses water level without the switch getting wet.
GPIO: A logic pin on a small computer board, such as an Arduino or a Pi. It can light an LED. It cannot run a motor or a heater by itself.

Where people actually find it

3 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.

Harvest at a glance
From	Call	How many	How often	Where it sits
Headphones	Worth it	1	sometimes	The boom.
Webcam	Bonus	1	usually	Beside the lens.
Mobile phone	Leave it	1	usually	Microphone.

Worth pullingHeadphones1 · sometimes
In this particular machine
A capsule.
Where to look
The boom.
How to get it out
Note polarity.
The condition to expect
Good.
Bonus, if you are already in thereWebcam1 · usually
In this particular machine
A small capsule, if you have already broken the camera.
Where to look
Beside the lens.
How to get it out
Bias it.
The condition to expect
Good.
Leave it — present, not yours to reuseMobile phone1 · usually
In this particular machine
MEMS on a flex, not a simple electret, on anything recent.
Where to look
Microphone.
How to get it out
Model-specific.
The condition to expect
Hard.