the circuit is power through 12v supply , some times i want to program the arduino while the board is off . The problem is that usb is sending 5v to the arduino , while the rest of the ICs are off .
the ICs might be damaged due to signal coming from arduino pins causing power up (due to internal diodes used for esd protection) ,
what is the reliable solution to this problem
the only thing i have in mind is to add relays on all (20 GPIOs) of arduino that will connect these pins to the respective ICs when 12v is applied , but this is very costy and makes board larger and decrese reliability which is the most important factor for me now ! maybe some kind of signal solid state relay array could solve the problem ??
i use this with a self powered device on the USB.
As long as the USB device power is not enabled (USB suspend), only the USB device controller chip is powered by the USB.
After USB is enabled the rest of the hardware is powered by external supply.