Tacho feedback

Hi Folks

I’ve searched as much as I can but it’s tough reading so many good posts.

I would like your advice about connecting a DC brushed motor with a DC tacho motor attached.

The spec sheets of most of the controllers seem to indicate that tacho feedback will work but then the details disappear. It’s probably me being old and senile!!

So, my situation is that I’m looking for a bi-directional, 3A-ish velocity speed controller that can take DC tacho feedback.

I’m sure this is the place but would some kind soul point me in the right direction?

Many thanks



Have you considered our 3A motor controller with feedback or higher-power SMC04 controller with feedback? It sounds like these might be just what you’re looking for.

- Ben

Hi Ben

Thanks for that. I’m glad you mentioned the 3A controller. I’d read the data sheet but it seemed to me that the only feedback inputs were a positional pot or an optical disc.

So, forgive my stupidity, but am I right to suggest that the analogue feedback input can be either a positional pot or a dc tacho?

The reason for my confusion is that page 6 of the data sheet states that analog feedback needs to be 0-5v, whereas the dc tacho would deliver +v and -v depending on direction. How do I get around that problem?



Hi Ben

Have you missed my last post?

Still hoping for a reply.




The input on our feedback controllers is indeed just 0 to 5V, so you would have to scale and shift your tachometer output to fit in that range. That might be more hassle than it’s worth. Can you check with your motor manufacturer if they have a recommended controller for your motor? (If you find one, can you let us know about it?)

- Jan

Hi Jan and Ben

I stumbled on this circuit when searching for level shifting on the Interwebby.

It’s a voltage divider that lifts one side of the tacho to +2.5v therefore giving +5v for full clockwise speed and 0v for full anti-clockwise speed. Simple and elegant.

The left hand pot is to tweak for 2.5v at zero speed and the 10k pot adjusted to prevent the feedback voltage from exceeding 5v at maximum speed.

Good eh?



Thanks Keith, that is a really helpful little drawing, gonna try it immediately.
I know there should be something simple available…