I have an instrument that I am trying to integrate some pumps with. It has 3 Open Drain pins,a ground, and a +5V pin.
I've successfully used 3 NPN transistors to act as a +5V switch to drive a relay when the Open Drain pins are high.
I have a problem when the instrument first turns on (or recovers from a power failure). It turns all 3 Open Drain pins high and turns on all 3 relays until it finishes initializing. I'd like to avoid this.
My idea is to use one of the Open Drain lines to act as a +5V supply when it is low (the initialized state) so that the other two lines will only be active when the instrument is fully initialized. How can I do that?