Using this shecmatic to drive some relays - works fione for a while then the relays start misbhaving. I'm a moron - the PCF is current based output thingy not a simple "heres 5v or 0v" for the ULN to work with.
As a result (of me not really reading the dtatasheet all that carefully) the base of the transistors in the ULN sit at around 2v when "on" - thats my issue! - So here's the question(s)
- Is there a hack I can do to this circuit (its laid onto a PCB proto) that will make it work for now? Something simple like a pullup/or something?
- Keeping the PCF to give my my "signals" what would you recommend as an output low side switch (as I am guessing the internal resistors in the ULN/transistor specs of the ULN are the issue) to drive some simple 12v automotive relays - maybe a hexfet or something?
- is there a replacement device that fits the PCF footprint, shares the same logic etc, but does a simple "heres 5v or 0v" output to drive the ULN properly?