This circuit was obtained in an old Elektor and can be adapted to use white power LEDs. The transistor must be equipped with a heat sink. The circuit has a battery charger.
Found in a Popular Electronics from the 90s, this circuit uses a double 555 to emit beeps when the...
The more sensitive the instrument used the better the sensitivity of the indicated meter. We...
Adafruit Breakout PDM Microphone This Adafruit tested microphone card is available from Mouser...