Tutorial DIY load cell brake pedal (short tuto)

just thought I'd post on here as I recently made this load cell mod for my G27 pedals. I am using the STM32 disco board as I am hoping to update to a direct drive wheel at some stage and use this board. I have used an INA126 amp as that was what i could get locally from Jaycar. When I opened game controller MMos the accelerator and clutch were working fine as the signal out from the pots increased as you pressed the pedals but the brake with the load cell was opposite, I don't know if the resistance is critical but I put a 4.7kohm resistor(what I had lying around) between pin 5 from the INA126 and ground. Now the voltage for the brake increases as you brake harder...hope this helps if anyone else has similar issues

I have attached the pcb I made for this project, there are 6 pins where the load cells attach, I used similar load cells to @RacingMat I just put 6 screw terminal block on the board

Really cool

Hi guys, to anyone looking into this, I just built one and it's awesome, had dramas using the wii-fit load cell but using same cells as racingmat worked first time, as for the difference it makes, was doing 1:00 around Barbagallo in a Huracan GT3 , same car same track now consistently on the high 57s so about 2 seconds a lap, major difference.

Thankyou racingmat for your post and information

Can somebody explain why these INA chips are so expensive? They seem to be £3-4 each just for the chip. I have a full multimeter (LCD screen, plastic case, probes etc) from China that cost something like £15 that can measure mv so how did they do that so cheaply?

I see the ricmotech loadcell kit at a whopping $130 managed to use a MCP6231 at one point, that chip costs £0.24. I am unsure if they still use that chip as they seem to have revised the PCB. Is this chip suitable?

I managed to buy one of these loadcells very cheap and am unsure what chip I should buy https://www.omega.co.uk/pptst/LCFL.html could anyone advise? What are the important parameters, input voltage/excite voltage and output mv/v? Plugging these details in rs-compoents Instrumentation Amplifiers section has me going in circles.

Would the INA129 be a suitable chip? There is a cheap module (£2.50-£3.50) with the name of "CJMCU-29" which has a small trim pot plus the INA129 but not much else. Can't seem to DIY anything for less than double the cost.

Hello.
and since a little time I try different configurations for my brake pedal, from 20kg cell with ina 125, to the biggest 200kg cell with hx711, of this last I would like to make hx711 adjustable in sensitivity as you can do with ina125.
I already know the change from 10 to 80hz, but I can not make the brake heavy, with about 40kg of thrust already goes to 100% what I did not want, I took the big cell to have weight margin.
do you have any idea? I would not use ina125 because of the offset I have to adjust often ..

Anyone happen to have some finished ardunio code for the HX711 sensor? Its such a shame that people rarely put it up.

do someone have other option other than ina122 or ina125..??? (also analog output)
its hard and expensive in my place...

Got my Uno working with HX711 clone and Unojoy.
You will need to do some soldering to get the clone into 80 hz mode. The default 10hz lags for the axis
Lift pin 15. Add a 10k resistor and route it to Vcc 5v (could probably do it another way too but i dont know)

Threw in the code. Ill be adding for Ard Leo/micro once it arrives.

Code for HX711 loadcell and 2 analog axis. Ardunio leonardo/micro Need joystick lib and HX711 lib Based on JensSimPedals

Edit:

Ive been having and issue with the pedals waking up the computer and after some support we figured out it was the setAXIS calls. I have updated the code to include an if statement so that the call to set Axis only happens when its not equal to resting pedal. Its important that you use the println to check what your pot numbers are and input the correct ones in the

Code:

int lastBrakeValue = 0; 

and so on

https://github.com/MHeironimus/ArduinoJoystickLibrary
https://github.com/bogde/HX711

Code:

#include <HX711.h>
#include <Joystick.h>
#define calibration_factor -2300 // Do your calibration first. default 2300
#define DOUT  3
#define CLK  2
HX711 scale;
/*
For the true false flags, use this list. Its all in  Joystick.h
    bool includeXAxis = true,
    bool includeYAxis = true,
    bool includeZAxis = true,
    bool includeRxAxis = true,
    bool includeRyAxis = true,
    bool includeRzAxis = true,
    bool includeRudder = true,
    bool includeThrottle = true,
    bool includeAccelerator = true,
    bool includeBrake = true,
    bool includeSteering = true);
  */
Joystick_ Joystick(JOYSTICK_DEFAULT_REPORT_ID,
  JOYSTICK_TYPE_MULTI_AXIS, 4, 3,
  false, false, true, false, false, false,
  false, true, true, true, false);
 
 
// Variable
int throttle = A0;
// int brake = 2; / no need for this as we read directly from scale
int clutch = A1;

// **** INPUT YOUR VALUES HERE **********
int brake = 0;
int lastBrakeValue = 0;

int throttleValue = 0;
int lastThrottleValue = 270;

int clutchValue = 0;
int lastClutchvalue = 180;

// init joystick libary
void setup() {
  // Ranges are 1023 by default
   Joystick.setBrakeRange(0, 1023);
  Joystick.setThrottleRange(0, 1023);
  //Joystick.setZAxisRange(0, 1023);
 
  Joystick.begin();
  Serial.begin(38400);
 
  scale.begin(DOUT, CLK);
  scale.set_scale(calibration_factor);
  scale.tare();
}
void loop() {

// ***** USE THESE TO CHECK YOUR POT VALUES IN SERIAL MONITOR ****

    //Serial.println (brake);
    //Serial.println (throttleValue);
    //Serial.println (clutchValue);


// For the if else if statements below. Set these to match your numbers as instructed.
// If the value starts below 0 set it to 0. Or if its above 10 set it to 0


// ******** THROTTLE ***************

  throttleValue = analogRead(throttle);
 
     if (throttleValue > 666) {
    throttleValue = 670;
  }
    else if (throttleValue < 273) {
    throttleValue = 270;
  }
    if (lastThrottleValue != throttleValue) {
     Joystick.setThrottle(throttleValue);
     lastThrottleValue = throttleValue;
  }
   delay(1);
 
// *********  BRAKE **************

brake = scale.get_units(); // if the value is inverted put a - sign in front like -scale.get
 
   if (brake < 0 or brake < 8) {
    brake = 0;
  }
 
   if (lastBrakeValue != brake) {
     Joystick.setBrake(brake);
     lastBrakeValue = brake;
  }
  delay(1);
 
// ********** CLUTCH *************

   clutchValue = analogRead(clutch);
 
     if (clutchValue < 185) {
    clutchValue = 180;
  }
    if (lastClutchvalue != clutchValue) {
     Joystick.setZAxis(clutchValue);
     lastClutchvalue = clutchValue;
  }
  delay(1);
}

3 HX711 setup using the HX711-Multi lib https://github.com/compugician/hx711-multi

Edit. Possbily this needs a lot of tweaking. I know one person was doing this but has not given any more information on the project.


Few items to note: For reading input values uncomment these. You will also need to use these values to check for the correct numbers in the AXIS CONFIG IF OR statements for the channels to set a HW DZ to avoid spiking close to 0

Code:

// uncomment for debug in serial monitor. Set serial monitor baud to 38400
//Serial.print ("Throttle: \t"); (throttle);
//Serial.print ("brake: \t"); (brake);
//Serial.print ("Clutch: \t"); (clutch);

If your numbers are inverted add a - sign in front of all results[] in the AXIS CONFIG

I needed - for my setup but this code is set to the without any inversion as default

When you have the correct numbers remove the uncommented (remove /* and */) if else statements and input your numbers in the AXIS CONFIG

Example when uncommented.

Code:

  throttle = results[0] / throttleDiv ;
 if (throttle < 0 or throttle < 5) {
    throttle = 0;
  }
    else
    throttle = results[0] / throttleDiv ;
  Joystick.setThrottle(throttle);
  delay(1);

Code:

#include <Joystick.h>
#include "HX711-multi.h"
// Pins to the load cell amp
#define CLK 2      // clock pin to the load cell amp
#define DOUT1 3    // data pin to the first lca
#define DOUT2 4    // data pin to the second lca
#define DOUT3 5    // data pin to the third lca

#define TARE_TIMEOUT_SECONDS 4
byte DOUTS[3] = {DOUT1, DOUT2, DOUT3};
#define CHANNEL_COUNT sizeof(DOUTS)/sizeof(byte)
long int results[CHANNEL_COUNT];
HX711MULTI scales(CHANNEL_COUNT, DOUTS, CLK);

/*
For the true false flags, use this list. Its all in  Joystick.h
   bool includeXAxis = true,
   bool includeYAxis = true,
   bool includeZAxis = true,
   bool includeRxAxis = true,
   bool includeRyAxis = true,
   bool includeRzAxis = true,
   bool includeRudder = true,
   bool includeThrottle = true,
   bool includeAccelerator = true,
   bool includeBrake = true,
   bool includeSteering = true);
  */

Joystick_ Joystick(JOYSTICK_DEFAULT_REPORT_ID,
  JOYSTICK_TYPE_MULTI_AXIS, 4, 3,
  false, false, true, false, false, false,
  false, true, true, true, false);


// Variable
int throttle = 0;
int brake = 0;
int clutch = 0;


// Divides the large scale number to smaller so you keep the number less than 1024. Depending on what force you put on the pedal. Check in serial monitor by uncommenting the Serial.print above the statements.


int throttleDiv = 200; // check this in serial as its likely to high
int brakeDiv = 200;
int clutchDiv = 200;
// init joystick libary
void setup() {
  // Ranges are 1023 by default
  // Joystick.setBrakeRange(-300, 10230);
  //Joystick.setThrottleRange(0, 1023);
  //Joystick.setZAxisRange(0, 255);
  Joystick.begin();
  Serial.begin(115200);
  Serial.flush();
  pinMode(11,OUTPUT);
  tare();
}

void tare() {
  bool tareSuccessful = false;
  unsigned long tareStartTime = millis();
  while (!tareSuccessful && millis()<(tareStartTime+TARE_TIMEOUT_SECONDS*1000)) {
   tareSuccessful = scales.tare(20,10000);  //reject 'tare' if still ringing
  }
}
void sendRawData() {
  scales.read(results);
}

void loop() {
  sendRawData(); //this is for sending raw data, for where everything else is done in processing
  //on serial data (any data) re-tare
  if (Serial.available()>0) {
   while (Serial.available()) {
     Serial.read();
   }
   tare();
  }


//        README!
// If inverted add  - to the channel results.
// Do this to All results in axis config
// Fks: throttle = results[0] / throttleDiv ;
// to  throttle = -results[0] / throttleDiv ;
// uncomment for debug in serial monitor. Set serial monitor baud to 38400
Serial.print ("Throttle: ");
Serial.println (throttle);
Serial.print ("brake: ");
Serial.println (clutch);
Serial.print ("Clutch: ");
Serial.println (clutch);
//
//
// Its important that you check the values (using the unncomment for debug above.) on your setup and adjust the range of the HW deadzone here. Your numbers could be different
// If the throttle value starts below 0 set it to 0. Or if its above 5 set it to 0
// This fixes the slight drift and sets it to 0 if it starts below 0
//comment out the if and else statements to remove and see pure values in serial monitor, then //set your numbers for HW DZ in the IF statement

// Example
/*  throttle = results[0] / throttleDiv ;
  if (throttle < 0 or throttle < 5) {
   throttle = 0;
  }
   else
   throttle = results[0] / throttleDiv ;
  Joystick.setThrottle(throttle);
  delay(1);
*/


//****** AXIS CONFIG*****
// Throttle
  throttle = -results[0] / throttleDiv ;
  if (throttle < 0 or throttle < 5) {
   throttle = 0;
  }
   else
   throttle = -results[0] / throttleDiv ;
  Joystick.setThrottle(throttle);
  delay(1);
// Brake
  brake = -results[1] / brakeDiv ;
  if (brake < 0 or brake < 5) {
   brake = 0;
  }
   else
   clutch = -results[1] / brakeDiv ;
  Joystick.setBrake((brake));
   delay(1);
// Clutch
  clutch = -results[2] / clutchDiv ;
  if (clutch < 0 or clutch < 5) {
   clutch = 0;
  }
   else
   clutch =  -results[2] / clutchDiv ;
  Joystick.setZAxis((clutch));
   delay(1);
}

@Trigen Can i use hx711 with Arduino Pro Micro + your code

@Huan Nguyen Yup. Im using the Pro micro myself.

I've bought an ina125 amplifier..
Any hints on how to cable it?
First post shows how to do the work with a 122, which has 8 pins instead of 16 of the 125.
Thanks in advance!

@Trigen I would like to use your code for a load cell brake with a HX711 and an Arduino pro micro. Would you be able to help me with the connections between de HX711 and the pro micro? And which of your codes I could use best?

[USUARIO 31790]@Trigen[/USUARIO]
Me uno a la orden, ¿tiene un esquema de conexión con Arduino micro?

Sorry but i dont understand you.

Sorry I had the autotraductor activated.

I was wondering if I had the arduino micro and load cell and hx711 wiring