Mikkel C. Simonsen wrote:
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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.


Whats the problem with SMT ? The beasties you need are only 8 pin ones. MAX701 CSA is nice - PB input, and complementary reset outputs too.


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?


1.) 1n4148 are SIGNAL diodes - the transient voltage from the inductive kick can blow them apart (really - been there done that. Got laughed at. When boss is also father that really stings....but father has even better relay inductive kick tale, from when he was in training) use at least 1N4001, I prefer 1n4007.

The internal diodes are a way away from the relay. The inductive currents will flow in fast long loops BACK to the ULN2803 and generate more crud: The diodes (and RC filters) MUST be on the pins of the relay....

Incidentally, Allegro do some neat little serially addressed relay drivers that do the 595 and the 2803 in one box.
Steve