Hall effect sensors and sensing gear teeth.

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AJL Electronics
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Hall effect sensors and sensing gear teeth.

Post by AJL Electronics » Sun Aug 30, 2020 7:57 pm

This is a bit of a crossover between automotive and radio...

I have a cheap NOS aerial rotator with a faulty control box (destroyed its gear train), so I have to build a new one. The original design is primitive in the extreme, the motor is geared down to just under 1RPM (actually 77 seconds) and the control box has the same gear train and motor. The idea is that you run the controller round to its end stop and then wait for the motor to stall. Then you go to the opposite end stop and do the same. Then the two are sort of synchronised. Motors are 24V AC with two windings so that the direction can be reversed by switching feeds.

In order to build a new controller, I have to sense where the motor is. Various methods of doing that, from simple timing to a compass module. Having played with various ideas, I tried a Hall effect sensor in the hope that I could pick up the large gear teeth. That worked after a fashion but the sensor is polarity concious and so the pulses die at four places around the gear.

So my question is about ABS and crankshaft sensors. Do they care about magnetic polarity? I assume not else they would be totally unreliable. Should I be buying a cheap ABS sensor to try out?

The compass module may turn out to be the way to go but I have to build a housing for it and put it at the end of a non metallic stick' on the mast. Then because I need to get the signals into the playroom, I will have to build an Arduino into the motor housing and talk via serial to the one in the remote control box.

Comments welcome.


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Last edited by AJL Electronics on Sun Aug 30, 2020 8:04 pm, edited 3 times in total.


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Hall effect sensors and sensing gear teeth.

Post by scimjim » Sun Aug 30, 2020 8:02 pm

What about a photo-electric sensor like the Ti dizzy? Is there room on the end to mount a wheel?


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Hall effect sensors and sensing gear teeth.

Post by AJL Electronics » Sun Aug 30, 2020 9:50 pm

scimjim wrote:
Sun Aug 30, 2020 8:02 pm
What about a photo-electric sensor like the Ti dizzy? Is there room on the end to mount a wheel?
It's a thought but as with a pot which is my favourite option, it is the mechanical connection that is going to be the issue. I thought it would be easy to find a selection of gears and pullies with 1/4" bore but I was proved wrong.

The Hall effect sensor besides being polarity consious (concious?) seems to oscillate when no magnetic material is being sensed. I thought it was faulty until I was looking to buy another and found this review...
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Hall effect sensors and sensing gear teeth.

Post by philhoward » Sun Aug 30, 2020 10:00 pm

Crank sensors are polarity sensitive (well, Ford ones are).

Vauxhall ABS sensors are ten a penny and there’s a special relay available (the “orange” one) which acts as a full amplifier if you wish, giving you a buffered signal to play with.


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Hall effect sensors and sensing gear teeth.

Post by Old and Slow » Sun Aug 30, 2020 10:03 pm

Have you tried HPC Gears:
www.hpcgears.com
Mostly metric bores but some are 6mm that could be drilled/reamed out to suit?
Also, a cheap weather station probably has a simple encoder for wind direction, but might be only resolved to 22.5 or even 45 degrees.
Making an Op-Amp circuit with hysteresis isn't rocket science - seems a bit silly not to have included it.


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