This double tone generator uses a specific integrated circuit, having been found in a 1977 CMOS Cookbook. The transistors can be the BC548.
This circuit was originally recommended to operate with the emitter of the previous circuit but...
When the probes of this circuit meet water, the relay closes its contacts. The circuit is from a May...
The power supply shown can supply voltages of approximately 0 V to 12 V with a maximum current of 4.5 A,...