What is the lowest current way of inverting the output from a GPIO pin?
I have a solar board that has an add-on that can turn a USB port power off if a LiPO gets below 3.3v. The problem is, they added the ability to control this battery-based switching using a two pin connector for 'Enable' and 'Control' (when Enable is 'high', control is ignored and the USB is turned off [if on] whenever the voltage drops below 3.3v and turned back on [when off] when the voltage rises above 3.8v)
The problem is, I can't turn this mode 'on' when the Raspberry Pi is off. I can only turn it off when the Raspberry Pi is on.
I would like to be able to hook an inverter on the GPIO pin so that it is 'high' when the GPIO pin is 'low' but consume as little additional current as possible to do this. That way I can disable the battery switching as long as the RPi is on, read the voltage and safe-shutdown the pi if it gets to 3.3v. Then, when the Pi is off completely, the battery voltage will turn off via the USB device.