Here I have an automotive relay (from a scan of a workshop manual I'm afraid) which is rather more complexly wired up than the relays I'm familiar with. In this diagram:
L/Y - +12V
L - From the relay's switched live (a switch in the car)
L/B - Gets grounded if the car's ECU 'allows' the relay to be on
B/G - holds high if another condition is met (engine temp too high), to prevent the relay energising. (As far as I can tell...this is the correct logic for sure, not sure if it technically works that way!)
B/L - the load (2 loads in parallel)
8(?) - goes direct to ground
I understand how the relay works at the moment. However, what I plan is to cut (L) and insert a device which will prevent the relay energising unless some further conditions are met. This is achieved with some logic gates and an output transistor, which will 'join' L when my device allows it.
So far so simple?
What I can't tell is if I need a protection diode across the relay to protect my transistor? And if I do, would this interfere with the logic provided by the combination of L, L/B and B/G?
If this is a problem, would I be better using a small relay? Are these more immune to the relay closing?