This circuit was found in the September 1993 Electronics Now magazine. It is based on the 555 and powers an audible indicator.
This circuit was found in an English magazine from 1979. The magazine no longer exists, but the...
This circuit was found in an 80's EDN. The circuit uses a current common CMOS, the 4093 powering...
The sensor of this circuit found in Popular Electronics can be formed by a piece of fabric between two...