Issue with build relay computer

[Frank]

Hi,

Just finished my build of the relay computer. Very nice!
It is working but I have sometimes (at default speed "5") that the board, when running a program, (the PIC controller) is resetting itself.

Is this a known problem? Maybe power supply noise induced by the relays?
When I set the speed to "1" or "2", it will happen less. Set to "A" it will almost always fail after the execution of a few program lines.

The power supply (switching type) I use is a 12V/ 4A type so this should be more than enough amps.

Anybody some idea?

[Joe Allen]

I've not seen this. I had to deal with the relay switching noise, but it caused errors in the 74HC595 shift registers- the microcontrollers always stayed up.

Maybe the 5V is having an issue. The 5V current is all from the LEDs- can you make it fail by just entering all 8s, so that all segment are illuminated?

Maybe one of the 595 outputs is shorted to ground or something? So when a particular bit is set, it's killing the 5V?

Yeah, 12V/4A is more than enough- it works even with 12V / 1.5A.

[Frank]

Hi,

All 8's on the display didn't reset it.

I must clarify that I'm not using the recommended AXICOM relays but a cheap Chinese one (HUI-KE HK19F 12V-SHG type). I did pre-test them all; checking if all contacts work when activated.
Could this in some way reset the PIC?

I didn't measure the 5V with a scope for noise. Only with a quality digital multimeter (it's 5.02V), but I didn't see a voltage dip when the board reset occurs...

[Frank]

Replaced all the cheap relays with the AXICOM type and the board is working perfectly: just running the pi calculation program at speed "A" and it finished correctly... Yeah!

Also wrote a Python program to interface serially with the relay board to load large programs into it (like the pi calculation program).