I use an Arduino Nano USB-powered and 9V battery.
The standard circuit of Arduino is so that is always uses the input with the higher voltage.
I want to but that Arduino 9V battery only be used when there is no voltage on the USB port is available.
Know someone how I can do that?
Perhaps a simple circuit?
Hi Filippo
You are using an operational amplifier IC but refering to it as solid-state relay. The IC LM358 is an op amp while the number in the red arrow in post# 18 is refering it as CPC2317N which is a relay.