cheapo strain gauge

I've got a steering wheel and set of pedals for the computer (see link below). I'd like to modify the brake pedal because it doesn't work like a normal brake pedal, it works just like the clutch or accelerator going all the way to the floor. I presume the best option is a strain gauge. I've phone a couple of places and they can sell me something for over $200 but the set of scales I have in the bathroom has 4 of the things and it was something like $80. Where would I get something like that? How hard would it be to interface with the pedals that currently use a pot?

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Thanks, Michael

Reply to
Michael C
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Using a strain gauge is non-trivial - from my vague knowledge, it requires a wheatstone bridge, compensation and probably some filtering and amplification to make it compatible with your application.

What might be easier is to restrict the travel of the brake pedal and use a spring or torque rod to add the required resistance, then either use the existing pot with a linkage to magnify the range of movement, or use a different size pot and resistors to match up the range of resistance.

Reply to
Poxy

Thanks for the reply.

Is there anything off the shelf that would do all this? Hmmm maybe I could just use the internals of a set of scales..

That's possible but maybe a second option at the moment.

Reply to
Michael C

I've found these that are cheap enough and look easy to design a circuit for.

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I just need the voltage out of the circuit to go the other way, ie more pressure = less voltage

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Is there an easy way to do that?

Reply to
Michael C

just get a strong spring (say a surplus valve spring from an old car engine) and a short slide pot

you'll need to bolt your chair to the floor.

I saw a homemade load cell once, the guy had arranged resistance wire like guy ropes to support a pin at both ends

force || || HHHH "pin" \/ ZZZZ mounting bracket HH /HH\ \\// resistance wire (4 each end) / HH \ / HH \ ZZZZ HH ZZZZ \ HH / \ HH / \HH/ HH the 4 upper wires were connected in series to form a single resistor as were the 4 lower wires, the upper and lower resistances formed two legs of a wheatstone bridge.

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Bye.
   Jasen
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Reply to
jasen

I was overthinking it. :-)

Reply to
Michael C

I've done more than that, here's the complete setup :-)

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Does the pin move?

Michael

Reply to
Michael C

I noticed that.

Reply to
atec

incidentally try adding a subby under the seat .

Reply to
atec

are you sure? I thought thisd was connected to a joystick port...

Bye. Jasen

Reply to
jasen

I have. I've also got a bass shaker from jaycar that is bolted in but not hooked up as I need to organise an amp for it. I could get a car amp but would need 12V and the power supply would be a little pricey.

Reply to
Michael C

It's via usb. The existing pedal starts at approx 4.7 volts and goes down to

0.5 volts with the pedal depressed.
Reply to
Michael C

Jaycar have some decent amps check the web

Reply to
atec

A few millimetres. depends how tight you get the wires, if you put power through them they expand (eg: heat the bottom ones while tightening the top)

you don't get a very strong signal from it, it'll need quite a bit of amplification.

Bye. Jasen

Reply to
jasen

Seems easy enough... just add a unity gain inverting amp to the output of that circuit

--
Dave M
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Reply to
DaveM

You should be able to get unbonded strain gauges for way less than $200. You can then devise a mechanical setup that stresses a piece of metal as you apply force. Use 2 gauges, glue one on one side of the metal and one on the other but close to each other, so that they respond in opposition and apply some temperature compensation. Then put them in a bridge with a power supply of a volt or two.

Strain gauge suppliers generally specify some sort of special glue. I've done this using ordinary araldite and it works fine.

You'll need a fairly senstive amplifier, with low drift. Typical gains would be upwards of 1000 if you want an output of a volt or more. I happened to have a nice AD chip free, if you use a common opamp you'll need to be careful in terms of stability. Someone here can surely advise.

Reply to
Bruce Varley

Won't that make it negative voltage?

Michael

Reply to
Michael C

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