ok im using the parallel port to run my circuit. on this circuit there are 3 relays now relays 1 and 2 are both 2 channel relays, relay 3 is a single channel relay. the voltage when i set one of the bits high is around 2.7 i think. any ways it enough to power the single channel relay to switch it on. but for the 2 channel relays it requires 3.1v - 5v so im going to add an external supply of 5v. my problem is how to i get a high signal from the port to send the 5v to the relay to power it up and hence turn it on?