This circuit is from old documentation, but it can be implemented with modern transistors such as 2N2222 for bipolar and BF124 for FET. The crystal determines the operating frequency.
When the sensor X1 is opened, the relay is energized. When waiting, the current drained is very...
Based on the LF256 operational amplifier, this circuit was found in the September 1989 issue of...
This circuit was found in a 1968’s Motorola documentation. The transistor is from that time. The...