Hi all.

I was thinking about using this linear potentiometer as a brake position sensor (BPS).

The idea is logging this data along with the rest of the sensors to join with the in board camera image and later see how I preformed (and could improve) at a trackday.

More data on this sensor here

Questions:
1) Am I using the right component for my needs?
2) how is it wired? (red / green / yellow)

Thanks in advance,
Joao

Sounds like the right thing for the brake position. The datasheet shows it's

red wiper
green retracted
yellow extended

by which it likely means the wiper is @ the green terminal when its fully retracted and its at the yellow terminal when fully extended. The main issue you may have is the throw of the pot vs the relatively small movements of a brake caliper....

a linear potentiometer would work quite well in this application. i doesnt matter about it being linear or not because the resistance will always be known for the corresponding amount of pedal movement.

usually the pins are laid out with 1 in the middle, and one on either end of the movement area.. you just need to use 1 wire attached to the middle, and one to one end. you can then test the resistance change with a multimeter when you turn the pot

Still think the problem is going to be the 10mm range of the potentiometer.....

Personally I think measuring brake force would be better... brake movement is more likely to be a noisy signal and might get effected by things expanding etc. Then again I suppose brake force might get effected by brake fade....

quote:

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Originally posted by Davey D
you just need to use 1 wire attached to the middle, and one to one end.

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quote:

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Originally posted by BenB
The main issue you may have is the throw of the pot vs the relatively small movements of a brake caliper....

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Yeap... log the movement of the pedal... like "how was I behaving..." vs "how should I behaving"


Sorry for my (huge) ignorance, but how would it be wired? Usually (IIRC) this sensors receive a +5v, a ground and the other is for output.

I dont understand how should I wire this

Thanks FOR ALL!
Joao

quote:

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Originally posted by BenB
Sounds like the right thing for the brake position. The datasheet shows it's

red wiper
green retracted
yellow extended

---

To use as a potential divider and log the variable voltage you would wire like this:


red wiper - to logger unit
green retracted - 5 Volts
yellow extended - 0 Volts

I have put 5 Volts but of course you can use higher or lower voltages - it depends on what the input to your logger unit is.

The green and yellow can be wired other way round;
it depends on whether you want the voltage to go from 0 to max as the plunger is extended or go from max to 0 V (is wired like this above).

Also since your logger unit is just reading voltage, you should use a potentiomenter between 1 and 10 K ohm value.

MANY MANY thanks!

Joao

Sorry, but one last doubt...

"0 volts" is the same as ground? Or has a special meaning?

quote:

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Originally posted by JoaoCaldeira
Sorry, but one last doubt...

"0 volts" is the same as ground? Or has a special meaning?

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^^^ for car application yes.

if we were talking home electronics, e.g. HiFi, then ground and 0 V would not necessarily be the same.

Could be connected to the brake pedal and would show pedal operation but may not be able to show the actual force as once the pads are in contact there should be little further movement of the pedal for increased brakingforce just pressure.I would think a pressure transducer plumbed into the brake line would be better but not lowcost.
Paul

quote:

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Personally I think measuring brake force would be better... brake movement is more likely to be a noisy signal and might get effected by things expanding etc. Then again I suppose brake force might get effected by brake fade....

---

I'll be adding a MQ200-PRO so the accelaration part is already covered.

Well... it will be pedal travel rather than pedal pressure... it's not a pro thing... it's just to give an idea of what I'm doing wrong...


Cheers all,
Joao

Mount it away from pedal with a crank arm fitted to the pot spindle to extend the working range.

Then use a direct connection from crank to pedal using lightweight material, say perspex or plastic.

This will increase the wiper range if done correctly.

There are linear pots available as 'piston' design. Similar to the gas lifters for hatchbacks but much smaller and obviously a linear pot.

See here http://www.celesco.com/linearpot/?gclid=CPrDqsfS05YCFRqH1Qod9zCb2g

http://www.transducersdirect.com/HeleoCart/Products/Default.aspx?sq=IxtvrI6BZNJ%2faC0J6KsW2T2eIH4lJzR0DffVgCfMFuw%3d&category=In+Cylinder+Lin ear+Transducers

Hope that makes sense.

Personally I would go for a pressure transducer in brake line.





[Edited on 1/11/08 by Rob Lane]