This circuit was found in a Ferranti documentation from 1969. The transistors are common types of the company at the time. Smaller equivalents may be used. The output power is of the order of 150 mW.
This circuit was found in a 1965 General Electric manual. What it does is give a warning if you...
The sensor in this circuit is a BA315 diode. Other diodes can be experimented, but this is one...
This circuit turns on your car's backlight when a vehicle coming from behind gets too close to it...