cheapo strain gauge

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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.

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.

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

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

Is there an easy way to do that?

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.

I was overthinking it. :-)

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

Does the pin move?

Michael

I noticed that.

incidentally try adding a subby under the seat .

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

Bye. 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.

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

Jaycar have some decent amps check the web

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

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

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.

Won't that make it negative voltage?

Michael