This interesting circuit for the RDA8851 allows you to obtain two volumes with a simple touch. The circuit is from an Electronics Now from December 1988. Note the amplifier voltages.
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,...