IO Pins are shortly set to on when external powered

Hi!I use 2 IO Pi boards which are connected to 16Port Relais Boards (5v)Because i want to staple up more IO PI's i decided to use external power connector (5V) and removed the Power Jumper at both boards.With the external 5V power i am powering the IO PI's and the Relais board'sWhen i plug in the external power all relays a shorty on for approx. 0.5 sec. (just a ticker)I think this behavior is triggered by the io pi because when i remove the data cable the relaisboard stays in 0 state when powering.Everything else is working fine then ( on / off / ...)How can i get rid of this short power ticker ?Please helpMany thxlg oliverP.S. The problem is that it would be a problem for most of the devices connected to the relays board when there is a short trigger when powering on.

Hi Oliver

Would it be possible to power the Raspberry Pi from the same 5V supply as the IO Pis and the relay boards?

The problem could be that if the Raspberry Pi is already powered when the IO Pi is unpowered then the I2C level converter will still be supplying about 2.6V to the I2C pins on the IO Pi chips. This could be causing the IO chips to pull the output pins high while the chip initialises. If you use the same supply for the Raspberry Pi and the IO chip or can make sure the two separate supplies switch on at the same time this should solve the problem.

There are a couple of ways you could connect the power supply up to the IO Pis and the Raspberry Pi, you could use separate cables to connect to the IO Pi boards and the Raspberry Pi while leaving the jumpers disconnected, this would mean that while they all receive the same power you wouldn't have the problem of the power back feeding into the Raspberry Pi from the IO Pi.

Alternatively, you could connect the power to the two IO Pi boards and leave one of the jumpers connected so the Raspberry Pi is powered through the 5V pin on the GPIO port. The downside of this approach is it would be bypassing the input protection fuse on the Raspberry Pi so if you accidentally shorted one of the GPIO pins to ground you could damage the Raspberry Pi.

Many thx.Putting all together to one switch solved the problem. My problem was also: that i used 3 Power Supplys(One for Raspi, one for IOPI1 and relais board 1 and one for IOPI2 and relais board 2)Many thxlg oliver