SparkFun Forums

[blauweke]

Hi

I am working on a project to upgrade my brake pedal on my racing wheel setup. The position of the brake pedal is now being measure by a potentiometer, and the resistance is created by a spring.
I want to swap out the potentiometer with a load cell so the pedal input relies on the pressure i put on the pedal, rather than the position of it. This is better for a number of reasons.

Anyway, i can only put one load cell on it, and it has to be rather small. So i was thinking about the load cell SparkFun offers.(https://www.sparkfun.com/products/10245)
I've been doing some research and to my understanding you need a hx711 amplifier for a load cell to work properly. So i looked into that and all i can see is people using 2 or 4 of these load cells with these amplifiers to 'combine them'.
This is not an option for me. So i was wondering if you could use only one load cell with the hx711 board, or if i even need one at all if i'm only using one load cell.

Thanks in advance for your help.

Tom

[DanV]

Are you sure? The HX711 is for a single load cell.
The Load Sensor Combinator can connect as many as 4 HX711's together.
And it communicates maybe through serial (?) using 10 SamplesPerSecond or 80 SamplesPerSecond.
Having a hard time determining whether it's serial.

[blauweke]

So how do i connect the load cel t the board then? There's only 3 wires coming off te load cell and there's 5 inputs in the board.

[DanV]

Near as I can determine, the 'load cell' you provided a link to is, instead, a load sensor.
It's a 3-wire device that's more like a voltage divider than a wheatstone bridge (which is typical of the load cells (strain gauge) which I have used extensively on industrial equipment).
I have actually never seen a 3-wire 'load sensor' before.
I now believe that if you want to use the HX711, then you should shop for a 4-wire device instead of the one you linked to.

But, then, that's just my opinion.

[mdancer]

Here's what I would try...

Based on the HX711 hookup guide, your sensor is essentially half of a wheatstone bridge, so grab a couple resistors (say 1k) to form the other half of the bridge. Hook them up like in the image below, and presto! you now have a four wire load cell.

Note: I have not tried this myself, I just think it will work in theory, i.e. don't blame me if it doesn't work.

Good luck!

load_sensor.png

[blauweke]

Thanks for your help!

I'll give the circuit you gave me a shot, thanks for your time.