This circuit uses a crystal phone and can be built with more modern transistors like the BC548. The original circuit is from a 1979 publication and is powered with only two AA or AAA batteries.
This sonic, sound or vox switch uses common SCR and transistors can be BC548 or equivalent. The...
This circuit allows you to use a calculator as a timer by directly activating a sum key with...
This circuit is from the time when photos were revealed in darkrooms. We found it in a 1968...