This circuit was found in a 73 magazine for radio amateurs of the 90s. The circuit uses two types of indicators, the diodes are for general use. The power supply is 5 V.
We found this circuit in a 1998 documentation. It tests common household appliances to see if they...
This circuit uses a triac to detect the level of a reservoir, and a sensitive SCR connected to the...
We found this circuit in an English publication from 1980. The transistor can be either the BC548...