I have a 12VDC automotive relay controlled by an open-collector NPN output on a remote device. I would like to be able to have an indication of when the relay is activated. I tried (and failed) the following:
- 12V buzzer in series with the relay - sound indication OK but relay is not being activated.
- 12V buzzer in parallel with the relay - open-collector does cut-off, sound and relay are activated continuously (this is weird). Once the buzzer is disconnected, the open-collector will cut-off in a couple of seconds.
- 12V LED in series with the relay - visual indication weak (compared to regular led light), relay is not being activated.
- 12V LED in parallel with the relay - visual indication OK, relay activated/deactivated OK, LED dead after one run (I suspect due to relay not having a suppression diode).
How can I have an indication of the relay's state? I would prefer to use the control information, not the relay output.