Digital IO Board freeze

Mark Mara

I have a couple of projects that use the Parallax Digital IO Board (Sharp solid state relays) controlled by code running on a C3. They work as expected except for one issue. Once the project is powered up and running, if a load is manually connected or disconnected (e.g. manual switch switch in the line between the Sharp relay and the controlled device) the digital IO board freezes with all relays on. The code on the C3 continues to run fine. The IO board can be reset via software or with a power cycle.

I am not a hardware guy so I may have done something stupid, but the wiring is pretty simple. I bring the the hot lines directly from a sub-panel to the Sharp relays, ground and neutral go directly to the controlled devices. The C3 is communicating with the IO board via the serial interface.

I don't really need to switch the lines manually, but I am curious as to why this happening?

--markM

davejames

...sounds like all the latches on the I/O board are being commanded to turn on. What could cause this? I'd scope out the power and ground lines to the I/O board and make sure there's no nasty noise occurring when the relays switch the load.

erco

Is your power supply plugged into the same mains being switched? Have you tried a battery supply to isolate from power spikes? How much power/current are your relays switching?

Mark Mara

Thanks for the help.

Is your power supply plugged into the same mains being switched?

The power supply for the relays is a 12 volt wall wart plugged into a circuited from the same sub-pannel as the lines being switched, but the lines are on different circuit breakers. The IO board logic is powered by 3.3 volts from the C3. The C3 is powered from a USB connection to a Mac Mini.

Have you tried a battery supply to isolate from power spikes?

No but I am currently charging a couple of battery packs.

How much power/current are your relays switching

4 amps on 2 relays and 1 amp on a third. The freeze happens if I switch any of the circuits.

I'll see what replacing the power supplies with batteries tells me. I can borrow a scope but I have zero experience using one.

--markM

Mark Mara

The problem goes away if the C3 is powered by a battery. If the C3 (and the DIOB because it gets its logic power from the C3) is powered by either the USB or from a wall wart the IO board freezes when I manual switch one of the controlled lines, however, the C3 continues to run fine.