RevPi Connect 5 and MIO unexpected behavior

[ptthomps]

Hi, we have a RevPi Connect 5 with MIO module, and we're experiencing some unexpected behavior from the digital inputs. We are using a Phoenix Contact STEP-UPS/24DC/24DC/3/46WH UPS to power the assembly, with a few rocker switches in place to test things. See the rough schematic below.

Now, if the power supply loses power, resulting in the ups providing 24v on Alarm to D3, 24V on Bat-Mode to D2, and 0V on Bat-Charge to D1, and if I then open switch A, the power light on the MIO module will flicker green rapidly. The voltage from D3 to ground and D2 to ground are also at 10.5V, rather than the expected 24v. If I instead open switch B, leaving switch A closed, the flickering does not occur, but I do measure 24V from the ground on the UPS to D1, D2, D3, and D4. In this case I would expect D1 and D4 to be 0V.

I discovered this anomaly because I had set up switch A to allow me to reboot the RevPi after shutting it down via the system shutdown command. I did not want to unplug and plug the Pi back in every time, so I thought I could just flip the switch to break and restore power to the devices. However when I did this, the power led on the MIO would do it's little green flicker thing, and the RevPi would not boot, or even light any LEDs.

It seems like what might be happening is that when the MIO is not powered at the 24V and 0V connectors on the bottom, current leaks between the digital terminals. Is this intended behavior?

Concerning the idea of restarting the RevPi after shutdown, is there an better way to achieve it that you can recommend?

Note: for the shutdown command, I am using python with the command

Code: Select all

os.system("sudo shutdown -h now")

[nicolaiB]

Did you use the MIO GND for the digital output or the system ground? You need to use the GND potential from the MIO IO connector.

Nicolai

[ptthomps]

Did you use the MIO GND for the digital output or the system ground? You need to use the GND potential from the MIO IO connector.

Nicolai

I tried both with the MIO's GND terminal bridged to my 0V connection, and without. The result was the same in both cases. To clarify, the digital channels on the MIO are acting as inputs, receiving the signal from the UPS signal terminals.