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How to wire a preset counter to a dc motor? Answered

I have a dc motor and a counter to count revolutions. I want the dc motor to shut down automatically when the motor has reached a certain number of revolutions. The counter has the ability to do this but I don't know how to wire the motor to make this happen.

I am controlling the motor with a pwm. 

The counter is a Sestos. 


A reflective sensor is one of the easiest ways to accomplish this.. One merely applies a strip of reflective paint to the shaft and watches it with a reflective sensor mounted as a pickup. Many have a ttl level output, but if not, the sub scuircuit is also a relatively easy bit. Push that logic level signal into a counter and program the counter to issue a pulse for turn off after N counts (or better, use a uC). The stop signal would simply lift a latch in a latching relay. (ie, interrupt the hold signal)


2 years ago

What kind of a sensor are you using to count motor shaft revolutions ?

A magnetic pickup or a photocell pickup to feed pulses to pin_1or pin_2 of the Sestos_counter.


Something like this.


I'm using an optical sensor to count revolutions.

Here was my major misunderstanding. I didn't know the counter itself could be the relay needed to switch the motor off. I'll wire this up tomorrow and see if it works. Thank you!

I took you at your word that it was a small motor under a half amp. Motors starting up ( even under PWM ) will draw six to ten times the rated current.

While relay contacts can carry more current then they switch you need to understand they ( the contacts ) bounce and Arc while closing and Arc harder when opening although PWM interrupts that arc.

Steve has a very sage warning !

You have been short on the engineering details, perhaps you should consider that your Sestos internal relay could actually permanently weld its contacts in a position. The Satos contacts can handle 3A and your PMW can handle 5A.

Anyway a solution below.


I've tried to provide all engineering details.

I thought the point of the PWM was to provide soft starts and so avoid current spikes as seen in other variac applications. I can obviously be wrong but that was my impression.

Either way, thanks for the updated layout. That does make sense.

No, not unless its specifically stated, the sort of PWM you have there isn't a soft starter.

And another method that is self latching is showen here.

That o.001uF disc capacitor helps the contact bounce of the Sestos relay.

The 1N4002 diode absorbs relay coil turn off voltage transient spikes.


better to use the motor on/off switch, not the motor current on the tiny relay in the sestis counter.

Wait a moment, I'll have to check my crystal ball....

Hmm, seems to be a problem with the crystal ball, all I see in the clouds is a big sign saying:
Not enough information to process!

More info needed.

What "counter", for a start ?

Are you being deliberately unhelpful ? Sestos make dozens of different counters and meters. Exact model number

What is this "PWM" of which you speak ? From a computer, or another off the shelf module ?

OK, so slowly we get the story. Describe what you want to do, both for our benefit, and yours. Does this work ?

"I want to be able to set a count on the Sestos counter, press a button, and a motor spin for the count revs, then stop"

Wire the the? The The as in the English pop band in the 80s? I think they were wired er.. weird enough.