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hooking up an open collector?

Greetings,

I've a couple of 12V motors that include Honeywell SS443A tach sensors. I'm trying to hook the sensors up to a PIC16F876 with no luck. I've the motors working just fine.

There are three sensor wires as follows:

orange - +5v blue - ground brown - sensor open-collector output

as instructed, I'm using a 10K pull-up to +5V and would expect the brown to go high/low/high but never see it change from about 0.36v. It's only rotating at 25RPM so I'd expect to see some change assuming the tach only counts complete revolutions.

Any thoughts?

Reply to
Kyle York
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  1. Why do you assume there is only one pulse per revolution? A Hall effect sensor could be actuated by gear teeth and produce many pulses per revolution. What are you using to monitor the tach output - voltmeter, oscilloscope?

  1. Here is the data sheet for the SS443A. Since if it is an open collector output you should be able to do what you describe using a pullup on the collector output to get the output to go from 0V to 5V. You put the pullup on the collector output and not the +5V power, right?

Mitch Berks> Greetings,

Reply to
Mitch Berkson

The resistor should go from the open collector output to +5V. The open collector output also goes to the PIC input. It sounds like your original description was right. I was just making sure.

Another thing you might try is connecting the pullup to a different voltage (12V?) and see if that has any effect on the output.

Maybe the magnet is misaligned and not activating the sensor? Do you have access to the sensor to try placing a magnet right next to it?

Mitch Berkson

Reply to
Mitch Berkson

Thanks. At least I got one part right.

Here's what I've found: the output from the sensor is normally 0.4v (using a 5v source). When the magnet is over the sensor, the output drops to 0.03v.

I'm a *complete* novice, so I'm probably thinking about this incorrectly, but should the multimeter be reading 5v when the output is close to 0, and 0 when the output is at 0.4? Is the problem that the ouput never goes to 0.0?

Reply to
Kyle York

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