The use of field effect transistors in this circuit improves its performance. This configuration is from a 1975 circuit manual. The transistor can be any general-purpose FET such as MPF102 or BF245.
We found this circuit in the 1964 RCA transistors manual. The sensor may be a common LDR and the...
This circuit is from a 1991 publication, but it can be assembled with more modern components. We...
Found in a 90s Maxim documentation, this circuit disconnects the battery in case of overload. The...