I'm sure this is a common problem but I've searched and searched and can't find the answer. or perhaps, I have come across the answer, but I didn't have the underpinning knowledge to be able to understand said answer...
Basically, I have an arduino running off a battery.
To charge the battery, I'm using a USB cable.
What I'm trying to achieve, is when the USB cable is plugged in, the arduino is powered from this and disconnected from the battery.
I have very limited space some I'm trying to achieve this using as few components as possible.
A P-Channel MOSFET works, kind of. However, the problem here is that for the gate to be closed, a negative voltage needs to be applied. I want something where the gate is closed even when left floating.
Really, what I (think I) want is a normally closed switch between the battery and arduino, but use the +5v from USB to open the switch.
I found this image which describes my problem, but not the answer:
