This circuit that has a response from 10 Hz to 700 kHz was found in Philips documentation from 1968. Dual transistors can be replaced by matched pairs.
This circuit makes use of an old Texas Instruments component. The buzzer is also from the era. The...
Published in Popular Electronics with the curious name of Obnoxious Noisemaker, this 1968 circuit...
This circuit turns on your car's backlight when a vehicle coming from behind gets too close to it...