Thread: relays & computers

I think we have been over this already. Try searching the forum.

could you please tell me which keywords to use? I've tried relay LPT parallel boot, but couldn't find something that resembles my problem

Most motherboards do this, if not all. Just off the top of my head, you could build a 30 second delay into the circuit so that it is not active until 30 seconds after it is powered up...

I solved this problem by having an XOR gate attached to two lines of the parallel port. You then need to modify your software to set the lines to be different before the relay will switch. Most parallel port resets will reset all data lines to the same thing.


Rob

Rob or/and Aaron,

would you mind telling me how I would go about your solutions?

other question, are all outputs reset? I do need 8 outputs, so if I go with rob's idea could I use one of the other outputs on the parallel ports?.

And yet another question,
How would I create a pulse, derived from the ACC power, to switch on my ATX mobo? I tried to figure out which part of the much spoken poweroff delay circuit, but can't find out which part is responsible for the translation from 12V continuously to a 12V pulse.

thanks guys!

Originally posted by marsjell
Rob or/and Aaron,

would you mind telling me how I would go about your solutions?

My solution involves getting an XOR gate (74LS86 would do the job), tieing each of the two inputs to data lines out of the parallel port, and then use the output of the XOR gate to drive a transistor to switch your relay. I actually ended up building an equivalent circuit from a bunch of NAND gates (74LS00) since I didn't have any '86s in my box of bits, but the effect is the same.

There are more output lines on a parallel port than the 8 data lines (try strobe for example).


Rob

Rob, I know that there are more ouputs, what I'm wondering is if they also get reset the same way as the data outputs, sothat I could use these for "the other input" of the XOR's ?

Originally posted by marsjell
Rob, I know that there are more ouputs, what I'm wondering is if they also get reset the same way as the data outputs, sothat I could use these for "the other input" of the XOR's ?

I don't know, it's probably motherboard specific, since some have implicit inverts from the control registers to the actual output pins. Might I suggest some investigation using a multimeter?


Rob

I like Rob's idea better than mine, but mine would simply involve a 555 timer set for 30 seconds or so. The output of the timer goes to the "enable" line (through a transistor buffer, of course) of the buffer chip you are using to interface to the port.