Depends. Typically, an open collector output is negative-true. That is, it would go low when the output relay is on. That is the opposite logic polarity from previous posts.
Depends. Typically, an open collector output is negative-true. That is, it would go low when the output relay is on. That is the opposite logic polarity from previous posts.
It doesn't require negative-true, but that is the traditional mode because the only active element pulls down. There is nothing preventing an NPN open collector output being positive-true, but you will have to make sure the pull up resistor is somewhere. Note that the pull up resistor can be to any voltage the transistor can withstand; it is not limited to the Vcc value of the driving circuit.
Analogkid, I had been chewing on a decent answer to your post #63 and you send me #64: a big thank you! Yes, that will do it. I have learned a lot during this thread.
Meanwhile I have been mulling on another circuit, for LDR sensors but that is part of another topic.