This switch automatically turns the amplifier for a analog volt meter on when there ia current flowing into the bridge rectifier and signal input wires turning on the opamp(included in the circuit coming soon), by doing that the 2 9v battery will last a long time. Even without flicking the switch or by removing the battery the circuit will be drawing nanoamps when no signal is being measured. Just connect the bridge rectifier in parallel with ground and signal input this is just part of the circuit, rest coming soon,subscribe to uln2803 on Twitter to be notified when the project is on my website and video
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