Being There

(Updated 2024.07: New design features a quick release base designed for my 4080 profile rig. Get the stl files here: https://www.printables.com/model/453287-load-cell-sim-racing-handbrake-updated-202408)

I finally got ’round-tuit. I’d picked up a 10kg load cell and HX711 load cell amplifier from SparkFun a couple of years ago, but as is often the case, multiple other shiny new projects grabbed my attention. The lack of an easy way to fabricate many of the parts had something to do with not getting ’round-tuit as well.

So, now that I’ve a 3D printer, I decided it was time to retire the trusty old handbrake I’d built back in 2019 and build a new one.

I soldered up the HX711, a HiLetgo Pro Micro Arduino clone (Arduino Leonardo board in the IDE), and a header for the load cell onto protoboard… and made the first mistake.

The HX711 ships jumpered to run at 10 Hz, which is fine for a scale, but way too slow for a handbrake. See that trace right above where it says “RATE”. Well, it needs to be cut to run the HX711 at 80 Hz. So, rather than desolder everything, I very carefully drilled a hole through the back of the protoboard and cut the trace. Don’t do it this way – much easier to cut it first. <g>

Next, I designed a test base, attached the load cell to a piece of wood, and bolted it to the rig to see if it was strong enough. Nothing broke, so I proceeded to write the code.

Testing setup

The code is nothing fancy, just used the MHeironimus Arduino joystick library and the bogde HX71 libraries. Read data, scale it, ignore low level noise, and send to the PC when the value changes.

With the code and the test base working I got to designing the final base and lever. The final base included a place to mount the PCB.

Base with PCB mount

Rather than use a spring, I printed a block of TPU which goes in front of the lever. I printed a few, changing the print density until I liked the amount of squish it provided.

Test rig

The Lever

The lower part of the printed lever has a pair of press fit 608 skateboard bearings on either side to spread the load. The groove down the side is for the load cell wiring. The opening to the inside is wide enough to slip the five pin Dupont connector through.

Press fit bearings in vise

I decided the first upper lever was a bit too bulky and a bit too tall, so I made another with some taper that was a bit shorter.

Original upper lever

Tape covers wire – will hot glue later

Slimmer upper handle

The holes on the countersink side are supposed to be clearance holes. Depending on how it prints, you may have to chase them with a reamer or drill. The holes on the far side from the countersinks are supposed to be tight enough that they are threaded by the screws.

Designed and printed a grip in TPU. The grip for the first lever had a domed top, which I decided I didn’t care for, so I made the grip for the slim lever flat on top.

Did not like the domed top

Code

The code is quite simple. All the heavy lifting is done in the joystick and HX711 libraries. You can get a copy here – Analog-E-Brake-Load-Cell

You may be happy with the settings I used for SCALE_FACTOR and NOISE, but to determine these yourself just build with DEBUG and CALIBRATE defined. I’d initially set NOISE to 10, but discovered that the vibration of the rig while driving was enough to generate readings as high as 150, so I bumped that up to 250.

// Analog eBrake-Handbrake using hx711 to read load cell

// #define DEBUG
// #define CALIBRATE

#include "Joystick.h"	// https://github.com/MHeironimus/ArduinoJoystickLibrary
#include "HX711.h" 		// https://github.com/bogde/HX711

#define LOADCELL_DOUT_PIN  3
#define LOADCELL_SCK_PIN  2

HX711 scale;

// max joystick (32767) divided by max HX711 reading (1,000,000) by experiment
#define SCALE_FACTOR	0.032767

// noise level determined by experiment, DEBUG & CALIBRATE defined
#define NOISE 		250

#define BUTTONS		0
#define HATS		0

Joystick_ Joystick(JOYSTICK_DEFAULT_REPORT_ID, JOYSTICK_TYPE_JOYSTICK, BUTTONS, HATS,
	false, false, false, false, false, false, false, false, false, true, false);
//  X      Y      Z      Rx     Ry     Rz     Rudder Throt  Accel  Brake  Steering

long offset;

void setup()
{
	Joystick.setBrakeRange(0, 32767);
	Joystick.begin();
	#if defined(DEBUG)
	Serial.begin(115200);
	#endif

	scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);

	offset = scale.read_average(10);	// zero out offset at startup

	Joystick.setBrake(0);		// start at zero brake
}

#if defined(CALIBRATE)
	long reading = 0;
#endif

long lastVal = 0;

void loop()
{
	if (scale.is_ready()) {
		long mapped = (long)((float) (abs(scale.read() - offset)) * SCALE_FACTOR);

		if (mapped > 32767)
			mapped = 32767;

		#if defined(CALIBRATE)
		/* calibration:
		 NOISE
		 Power up with no pressure on the cell, wait a bit and record the noise level. Note
		  that it is very sensitive - it will pick up vibrations of your rig. You might wish
		  to drive a bit with the calibration code running. Update NOISE value.

		 SCALE_FACTOR
		 Apply reasonable pressure on lever. If it maxes out (32767) too easily change
 		 SCALE_FACTOR to bring it in range.
		*/
		if (mapped > reading) {
			reading = mapped;
			Serial.print("Value: ");
			Serial.println(reading);
		}
		#else
		if (mapped <= NOISE)
			mapped = 0;
		if (lastVal != mapped) {		// don't transmit data unless changed
			Joystick.setBrake(mapped);
			lastVal = mapped;
		}
		#endif
	} else {
		delay(1);
	}
}

Parts

• 60 x 40 mm proto PCB
• HiLetgo Arduino Pro Micro clone (https://tinyurl.com/3md9wk75)
• HX711 load cell amplifier (https://www.sparkfun.com/products/13879)
• 2 608 roller skate bearings
• 10 Kg load cell (https://www.sparkfun.com/products/13329)
• 2″ 5/16 bolt and nut
• 2 M4x30 screws
• 2 M5x30 screws

Model Files

The model files are available at Printables.com

I just saw an ad for one of the commercial button boxes and they listed a great new feature – get more outputs from the rotary encoders by using their push buttons as shift keys. A great addition to my original button box.

As I’d recently been thinking about wanting more rotary encoders and having more buttons than I knew what to do with, I thought it was a great idea to sacrifice four of the buttons to get four more rotary encoders.

It was just a simple matter of tracking the state of the four buttons and using that info to send different codes for the encoders if they were pressed. I’m still sending the button presses as well, so I can still choose whether to use the extra encoders or the buttons when I assign the buttons to controls in game.

There’s not all that much to doing a button box, so I’ll just publish the code here.

//BUTTON BOX
//USE w ProMicro
//Tested in WIN10 + Assetto Corsa
//AMSTUDIO
//20.8.17
// YouTube video: https://www.youtube.com/watch?v=Z7Sc4MJ8RPM

// 10/06/2019
// Bill Smithem
// Added additional button
// 4/4/2020
// Bill Smithem
// set debounce time to 50 (default was 10)
// 01/21/2021
// Bill Smtihem
// add "4 func" rotaries - different code sent if button pressed while turning. Tracked state of buttons 21-24
//  and used that to "shift" the rotary encoders. Note: we're still sending the button presses for the rotary
//  encoders, so mind that when assigning buttons in game.
// Number of "buttons" goes from 33 to 41

#include <Arduino.h>
#include <Keypad.h>
#include <Joystick.h>

#define ENABLE_PULLUPS
#define NUMROTARIES 4
#define NUMBUTTONS 25
#define NUMROWS 5
#define NUMCOLS 5

// Odd map is so buttons come out in numerical order, not scanning order. i.e. top left button is one, next is
//  two, etc. Just wired in the most convenient fashion and worked it out in the map.
byte buttons[NUMROWS][NUMCOLS] = {
  {5, 6, 17, 23, 12},
  {3, 4, 16, 22, 11},
  {9, 10, 19, 20, 14},
  {1, 2, 15, 21, 0},
  {7, 8, 18, 24, 13},
};

struct rotariesdef {
  byte pin1;
  byte pin2;
  int ccwchar;      // send this for CCW
  int cwchar;       //  this for CW
  int ccwPchar;     //  this for CCW with button pressed
  int cwPchar;      //  and this for CW with button pressed
  volatile unsigned char state;
};

rotariesdef rotaries[NUMROTARIES] {
  {0, 1, 32, 31, 40, 39, 0},
  {2, 3, 29, 30, 38, 37, 0},
  {4, 5, 27, 28, 36, 35, 0},
  {6, 7, 25, 26, 34, 33, 0},
};

#define DIR_CCW 0x10
#define DIR_CW 0x20
#define R_START 0x0

#ifdef HALF_STEP
#define R_CCW_BEGIN 0x1
#define R_CW_BEGIN 0x2
#define R_START_M 0x3
#define R_CW_BEGIN_M 0x4
#define R_CCW_BEGIN_M 0x5
const unsigned char ttable[6][4] = {
  // R_START (00)
  {R_START_M,            R_CW_BEGIN,     R_CCW_BEGIN,  R_START},
  // R_CCW_BEGIN
  {R_START_M | DIR_CCW, R_START,        R_CCW_BEGIN,  R_START},
  // R_CW_BEGIN
  {R_START_M | DIR_CW,  R_CW_BEGIN,     R_START,      R_START},
  // R_START_M (11)
  {R_START_M,            R_CCW_BEGIN_M,  R_CW_BEGIN_M, R_START},
  // R_CW_BEGIN_M
  {R_START_M,            R_START_M,      R_CW_BEGIN_M, R_START | DIR_CW},
  // R_CCW_BEGIN_M
  {R_START_M,            R_CCW_BEGIN_M,  R_START_M,    R_START | DIR_CCW},
};
#else
#define R_CW_FINAL 0x1
#define R_CW_BEGIN 0x2
#define R_CW_NEXT 0x3
#define R_CCW_BEGIN 0x4
#define R_CCW_FINAL 0x5
#define R_CCW_NEXT 0x6

const unsigned char ttable[7][4] = {
  // R_START
  {R_START,    R_CW_BEGIN,  R_CCW_BEGIN, R_START},
  // R_CW_FINAL
  {R_CW_NEXT,  R_START,     R_CW_FINAL,  R_START | DIR_CW},
  // R_CW_BEGIN
  {R_CW_NEXT,  R_CW_BEGIN,  R_START,     R_START},
  // R_CW_NEXT
  {R_CW_NEXT,  R_CW_BEGIN,  R_CW_FINAL,  R_START},
  // R_CCW_BEGIN
  {R_CCW_NEXT, R_START,     R_CCW_BEGIN, R_START},
  // R_CCW_FINAL
  {R_CCW_NEXT, R_CCW_FINAL, R_START,     R_START | DIR_CCW},
  // R_CCW_NEXT
  {R_CCW_NEXT, R_CCW_FINAL, R_CCW_BEGIN, R_START},
};
#endif

byte rowPins[NUMROWS] = {21, 20, 19, 18, 15};
byte colPins[NUMCOLS] = {14, 16, 10, 9, 8};

Keypad buttbx = Keypad( makeKeymap(buttons), rowPins, colPins, NUMROWS, NUMCOLS);

Joystick_ Joystick(JOYSTICK_DEFAULT_REPORT_ID,
                   JOYSTICK_TYPE_JOYSTICK, 41, 0,
                   false, false, false, false, false, false,
                   false, false, false, false, false);

void setup() {
  void rotary_init();

  Joystick.begin();
  rotary_init();
  buttbx.setDebounceTime(50);
}

void loop() {
  void CheckAllEncoders();
  void CheckAllButtons();

  CheckAllEncoders();

  CheckAllButtons();

}

// keep state of last four buttons (ones attached to rotaries)
KeyState rbState[] = { RELEASED, RELEASED, RELEASED, RELEASED };

void CheckAllButtons(void) {
  int kc;

  if (buttbx.getKeys())
  {
    for (int i = 0; i < LIST_MAX; i++)
    {
      if ( buttbx.key[i].stateChanged )
      {
        kc = buttbx.key[i].kchar - 21;        // track state of buttons 21-24 (switches on rotaries)
        switch (buttbx.key[i].kstate) {
        case PRESSED:
        case HOLD:
          Joystick.setButton(buttbx.key[i].kchar, 1);
          if (kc >= 0)
            rbState[kc] = PRESSED;
          break;
        case RELEASED:
        case IDLE:
          Joystick.setButton(buttbx.key[i].kchar, 0);
          if (kc >= 0)
            rbState[kc] = RELEASED;
          break;
        }
      }
    }
  }
}

void rotary_init() {
  for (int i = 0; i < NUMROTARIES; i++) {
    pinMode(rotaries[i].pin1, INPUT);
    pinMode(rotaries[i].pin2, INPUT);
#ifdef ENABLE_PULLUPS
    digitalWrite(rotaries[i].pin1, HIGH);
    digitalWrite(rotaries[i].pin2, HIGH);
#endif
  }
}

unsigned char rotary_process(int _i) {
  unsigned char pinstate = (digitalRead(rotaries[_i].pin2) << 1) | digitalRead(rotaries[_i].pin1);
  rotaries[_i].state = ttable[rotaries[_i].state & 0xf][pinstate];
  return (rotaries[_i].state & 0x30);
}

void CheckAllEncoders(void) {
  for (int i = 0; i < NUMROTARIES; i++) {
    unsigned char result = rotary_process(i);
    if (result == DIR_CCW) {
      // check if button pressed
      if (rbState[3-i] == PRESSED) {
        Joystick.setButton(rotaries[i].ccwPchar, 1); delay(50); Joystick.setButton(rotaries[i].ccwPchar, 0);
      } else {
        Joystick.setButton(rotaries[i].ccwchar, 1); delay(50); Joystick.setButton(rotaries[i].ccwchar, 0);
      }
    }
    if (result == DIR_CW) {
      if (rbState[3-i] == PRESSED) {
        Joystick.setButton(rotaries[i].cwPchar, 1); delay(50); Joystick.setButton(rotaries[i].cwPchar, 0);
      } else {
        Joystick.setButton(rotaries[i].cwchar, 1); delay(50); Joystick.setButton(rotaries[i].cwchar, 0);
      }
    }
  }
}