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ABS sensor pickup

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asfarley

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My goal: convert an ABS sensor output to a square wave suitable for a microcontroller, *without interfering with other systems reading the ABS sensor*.


All the simple circuits I've seen for converting ABS sensor output to a square wave tie one leg to ground. This makes sense if the sensor isn't used for anything else or if we're on a completely isolated circuit from the vehicle main power, but if an existing ABS computer is trying to bias the ABS sensor, tying one leg to ground would conflict with this, right?

Is there any safe way of splicing an ABS signal and converting to a square wave without interfering with an existing ABS computer?
 
tying one leg to ground would conflict with this, right?
Doesn't the ABS computer do that already?
What are the output characteristics of your ABS sensor (voltage, impedance,pulses per wheel rev...)?
 
Yes, I think ABS computers do tie one leg to ground and bias the other side. The problem is this requires testing the sensor bias polarity when hooking up my device. I'd prefer some circuit that was independent of the DC bias/polarity applied by the ABS computer. I don't know the ABS voltage/impedance because the particular ABS sensor I'm using isn't decided yet. I'm trying to come up with an input buffer that will have a good chance of accepting whatever ABS signal comes from the sensor, without interfering with the ABS computer and without measuring polarity when hooking it up.
 
really it depends on the type of system.
most are of a magneto resistive type which produces an a/c sine of not much more than 300mv.
 
Thanks folks... I kind of suspected there wasn't a solution that would work without knowing more details, just thought I'd ask anyway.
 
Where in the world are you ? In the UK , Vauxhall sell an ABS sensor amplifier which has a differential input (i.e. not grounded) if I remember rightly.

They are £15-£18
 
Standard comparators, such as the LM339 have a differential input. You should be able to connect inputs to the two ABS signals and generate a pulse signal from that. You would want to add a couple of resistors to provide a small amount of positive feedback for hysteresis.

What is the signal level from the ABS?
 
We've pretty much decided to keep the ABS sensors internal to our system instead of trying to interface with existing ABS sensors, so this is no longer a problem.

We will probably end up going with an LM339 or something very similar.

Thanks everyone for the advice!
 
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