Per Guldmann wrote:
-------------------------------
Hej Mikkel!

You have to fix several things:

Get a decent powersupply, and separate micro and relay supply.

A decent supply, yes. Is a seperate supply nescessary? If all 16 relays are on at the same time, they will draw 500mA. That shouldn't be a problem for a 7805T - or are you worried about transients when the relays switch on?

I guess a seperate regulator for the relays wouldn't be a large problem.

Get a propper supervisor ic, and use it for both micro and latches

Any suggestions? I will need both active high and active low reset outputs, and the thing has to be small (but not SMD) and cheap. I could use an inverter for the extra reset output, but there are no inverters (or other gates) used in the circuit, so I would have to add an extra chip just for that.

Use a diode - 1N4148 - over each relay, to kill the noise at the source.

The ULN2803 drivers have internal diodes, so I guess they can replace the 1N4148 diodes?

PCB real estate is expensive; we all know that. But it could easily becomme a lot more expensive to have a product fail due to lack of care.

I know, and I don't plan to make it fail :-)

BTW - is this a one of, or is it a thing to go in production? If so remember that the product must pass a EMC test!

So far it's just a test circuit so I don't have to worry about EMC - not yet at least...

Ha' en god søndag

Tak i lige måde

Best regards,

Mikkel C. Simonsen