Help with open collector output

[Alec_t]

Good to know it's working now.

 

[Old Steve]

Okay so ive figured out my i was using a 9v battery that was almost out of juice and hence why i was getting a lower output voltage than the assumed 9v supply. Put a fresh 9v battery in and it seems to give me a full 9v's output. Using a relay with the freewheel diode in place i can successfully control my 12v motor!

Glad to hear that it's working well. And that explains the puzzling voltage from the open-drain output.
Have you considered powering the receiver from the (larger, I assume) 12V battery, or is the motor and 12V battery a distance away? Then you wouldn't need to worry about regularly replacing 9V batteries. They don't have a very large capacity.

 

[starscream]

A 12v supply would certainly simplify the whole design but i wanted to keep the enclosure containing the receiver as small as possible hence the 9v battery.

 

[Old Steve]

A 12v supply would certainly simplify the whole design but i wanted to keep the enclosure containing the receiver as small as possible hence the 9v battery.

That's understandable. Is it possible to run the 12V wires back from the battery with the motor / relay wires? Just a thought.

 

[GPG]

I'd still dispense with the relay and drive the motor from the receiver.Just measure the voltage on the output driving a known current and you have the on resistance . Unless you are driving a large load it will be negligible. I'd expect it to be ~ .025Ω

That's understandable. Is it possible to run the 12V wires back from the battery with the motor / relay wires? Just a thought.

So would I as above