SensingBench electronicsUnplug and unscrew
Piezo disc
Also called piezo element, ultrasonic atomizer, pickup.
A brass disc with a ceramic layer. In musical cards and as a knock sensor it is a high-impedance pickup. In an ultrasonic humidifier it is a different part, driven at about 1.7 MHz by its own board, and it will not beep if you put 5 V DC on it.
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.
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.
| What to look for | Usual figure |
|---|---|
| Audio disc | Two electrodes. Tap it and a scope shows a voltage. As a sounder it wants a square wave, not DC. |
| Humidifier | A thick disc with a driver board. Keep the pair. The disc is a consumable and pits with use. |
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 knock or vibration sensor
- A crude pickup
- Fog, if you keep the ultrasonic driver
Leave this one when
The ceramic is cracked. Output collapses.
Buying a new one is the better idea when
A cased piezo buzzer if all you wanted was a beep.
How to tell if this one still works
Scope while tapping, for a sensor disc. For an atomizer, only run it with its board and with water, never dry for long.
Tools you will want: Scope or meter on AC.
Where people actually find it
1 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.
| From | Call | How many | How often | Where it sits |
|---|---|---|---|---|
| Ultrasonic humidifier | Worth it | 1 | always | Reservoir floor. |
- In this particular machine
- Ultrasonic atomizer, not a beeper. Pitted discs are the failure.
- Where to look
- Reservoir floor.
- How to get it out
- Keep the driver board with a good disc. A pitted one is a pattern, not a part.
- The condition to expect
- Often worn.