Seat Slide DC motor with sensor - how to interpret the signal?

I am kind of new to sensors and electronics in general. My project is as follows:

I have a set of car seat adjustment motors.

I want to set their positions as precise as possible via my Arduino (using my computer and USB, but that’s not the topic here).

They have 4 Pins each and I have a rough schematic (please see attachment).
I know how to start the motors: Putting 12V to FWD and BWD pins, polarity sets the direction.
But I don’t know how to interpret the SIG pin 2.
For the VCC pin 3, I think I need 12V, but:

  1. where to connect the Ground?
  2. what signal do I get and how to interpret it?

My first attempt:
I am expecting to get some sort of current step each time a magnet passes by the coil, like a hall sensor or alike.
Unfortunately I have neither a good multimeter nor an oscilloscope to measure something.

The resistance between pin 3 and 2 is 106kR or 20kR depending on the polarity of my multimeter.
I also measured 5.6kR once, so the resistance seems to be changing.

I also read about hall effect sensor interfaces like this MAX9621 but I don’t know how to deal with these.

It would be great if someone could give me a starting point, how to get a clean step-like signal out of this. Of course, it would be great to have a shield or a simple circuit to do that.

Thank you in advance,

Have you tried sending an email to Yeyang?

It could be some kind of current sensor telling you you've hit the travel limit and stalled the motor?

thanks for your answer.
Yes, I already tried that, but didn't get an answer yet (it's two weeks ago).

Your suggestion sounds reasonable, having a sensor to recognize the travel limit.

Have you ever actually gotten the motors to move? If not, I suspect your analysis of the pin usages might be incorrect.

travel/end limit in auto circuits is usually done by overcurrent detection from the motor stalling.
Vcc is probably for +12Vdc supply. Grounding FWD or BWD determines which way current is applied to the motor coils, and thus the direction of the 'slide'. the signal line is then likely an induced pulse to indicate revs of the armature. counting the pulses indicates travel distance, depending upon gearing.

You are NOT likely to be able to get a very precise positioning with this system. That ain't what it is made for....

Hi Splat,
thank you for your help.
I am able to start the motor by connecting FWD pin1 to anode and BWD pin4 to cathode. Changing the polarity also changes the direction.

I got a more complete schematic now:
The input called "VCC" on pin 3 is wired to a knot where all other motors VCC pins are wired to, called "Hall IC", which is then wired to a pin called "Sensor VCC".

That's why I believe the sensor got it's own VCC, independent by the motor's VCC.

your description of the motor direction/power application sounds like the sunroof circuit on an old Volvo I used to have. So, I'm ok with that. but I'm having problems with the rest of it. Lets see your improved schematic. the whole circuit.