Found in an English publication from the 1980s, this circuit can be built with equivalent transistors such as the BC549. The signal must be applied to an external amplifier.
Found in Radio Electronics from the 90s, this circuit uses a thermistor as a sensor that can have...
The scale of this scale uses LEDs, and its accuracy depends on the number of LEDs. We found this...
Found in American documentation from the 90s, this circuit generates sound bursts according to the...