We found this circuit in the October 1988 Radio Electronics magazine. The circuit is still current due to the components used, and changes can be made.
This circuit can use a pendulum sensor. We found this configuration in a 1994 publication. The...
This circuit is from a 1964 Electronic Design. The sensor is an LDR and the transistors are...
This circuit works both as a preamplifier and activates a relay when speaking in front of the...