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From https://www.eevblog.com/forum/beginners/treadmill-motor-controller-interfacing-with-arduino/?PHPSESSID=3mcu5kkmeatp7vb9bjn525v3c4

Hey this is an old thread, but I have done exactly the thing you are asking... in fact I found this post while searching for the treadmill controller and wanted to leave some info for the next person:
The comms interface for the controller isn't straight PWM, it uses RS-485. Here is a link to my writeup: https://elliotmade.com/2020/06/26/treadmill-controller-reverse-engineering/

I didn't completely reverse the protocol, but I figured out enough to run it. I never found any official documentation (not surprising), but also did not expect to. I left an arduino sketch there as well that can start/stop and control the speed. Couple other notes:
The controller gets mad without the encoder plugged in
If you don't send it a packet within a few seconds of booting, it also gets mad
It also requires continuous communication or it will stop (for safety). When stopped or at a steady state, you should continually send the same packet
The speed commands have to be ramped up. You can't go from 0-4000 in one step, rather you have to send some intermediate speeds as it accelerates (safety?)
Don't have to ramp down, just send a slower speed and it will coast until it reaches it
I'm an amateur at such things, so what I did is probably super dangerous... so watch out! (mine is on a belt grinder now, dangerous by design)

Cheers

See https://elliotmade.com/2020/06/26/treadmill-controller-reverse-engineering/

Speed to Byte Message:

MPH	Byte 1	Byte 2	Byte 3	Byte 4	Byte 5	Byte 6	Byte 7	Measured RPM
0.0	0	255	241	2	0	0	221	0
0.5	0 00	255 FF	241 F1	2 02	0 00	161 A1	16 10
0.6	0	255	241	2	0	195	201
0.7	0	255	241	2	0	230	186
0.8	0	255	241	2	1	8	144
0.9	0	255 FF	241 F1	2 02	1 01	42 2A	116 74
1.0	0	255	241	2	1	76	105	332
1.1	0	255	241	2	1	111	188
1.2	0	255	241	2	1	145	33
1.3	0	255	241	2	1	179	197
1.4	0	255	241	2	1	213	216
1.5	0	255	241	2	1	248	18
1.6	0	255	241	2	2	26	156
1.7	0	255	241	2	2	60	188
1.8	0	255	241	2	2	94	101
1.9	0	255	241	2	2	129	79
2.0	0	255	241	2	2	163	171	670
2.1	0	255	241	2	2	197	182
2.2	0	255	241	2	2	231	82
2.3	0	255	241	2	3	10	43
2.4	0	255	241	2	3	44	11
2.5	0	255	241	2	3	78	210
2.6	0	255	241	2	3	112	8
2.7	0	255	241	2	3	147	154
2.8	0	255	241	2	3	181	186
2.9	0	255	241	2	3	215	99
3.0	0	255	241	2	3	249	250	1016
3.1	0	255	241	2	4	28	96
3.2	0	255	241	2	4	62	132
3.3	0	255	241	2	4	96	229
3.4	0	255	241	2	4	130	70
3.5	0	255	241	2	4	165	87
3.6	0	255	241	2	4	199	142
3.7	0	255	241	2	4	233	23
3.8	0	255	241	2	5	11	64
3.9	0	255	241	2	5	46	51
4.0	0	255	241	2	5	80	212	1358
4.1	0	255	241	2	5	114	48
4.2	0	255	241	2	5	148	87
4.3	0	255	241	2	5	183	130
4.4	0	255	241	2	5	217	38
4.5	0	255	241	2	5	251	194
4.6	0	255	241	2	6	29	136
4.7	0	255	241	2	6	64	186
4.8	0	255	241	2	6	98	94
4.9	0	255	241	2	6	132	57
5.0	0	255	241	2	6	166	221	1700
5.1	0	255	241	2	6	200	121
5.2	0	255	241	2	6	235	172
5.3	0	255	241	2	7	13	63
5.4	0	255	241	2	7	47	219
5.5	0	255	241	2	7	81	60
5.6	0	255	241	2	7	116	79
5.7	0	255	241	2	7	150	236
5.8	0	255	241	2	7	184	117
5.9	0	255	241	2	7	218	172
6.0	0	255	241	2	7	253	189	2042
6.1	0	255	241	2	8	31	135
6.2	0	255	241	2	8	65	230
6.3	0	255	241	2	8	99	2
6.4	0	255	241	2	8	134	54
6.5	0	255	241	2	8	164	175
6.6	0	255	241	2	8	202	118
6.7	0	255	241	2	8	236	86
6.8	0	255	241	2	9	15	112
6.9	0	255	241	2	9	49	234
7.0	0	255	241	2	9	83	51	2385
7.1	0	255	241	2	9	117	19
7.2	0	255	241	2	9	152	158
7.3	0	255	241	2	9	186	122
7.4	0	255	241	2	9	220	103
7.5	0	255	241	2	9	254	131
7.6	0	255	241	2	10	33	132
7.7	0	255	241	2	10	67	93
7.8	0	255	241	2	10	101	125
7.9	0	255	241	2	10	135	222
8.0	0	255	241	2	10	170	20	2725
8.1	0	255	241	2	10	204	9
8.2	0	255	241	2	10	238	237
8.3	0	255	241	2	11	16	132
8.4	0	255	241	2	11	51	81
8.5	0	255	241	2	11	85	76
8.6	0	255	241	2	11	119	168
8.7	0	255	241	2	11	153	118
8.8	0	255	241	2	11	188	5
8.9	0	255	241	2	11	222	220
9.0	0	255	241	2	12	0	105	3070
9.1	0	255	241	2	12	34	141
9.2	0	255	241	2	12	101	161
9.3	0	255	241	2	12	103	69
9.4	0	255	241	2	12	137	139
9.5	0	255	241	2	12	171	127
9.6	0	255	241	2	12	206	49
9.7	0	255	241	2	12	240	235
9.8	0	255	241	2	13	18	188
9.9	0	255	241	2	13	52	156
10.0	0	255	241	2	13	87	116	3414
10.1	0	255	241	2	13	121	237
10.2	0	255	241	2	13	155	78
10.3	0	255	241	2	13	173	110
10.4	0	255	241	2	13	224	92
10.5	0	255	241	2	14	2	210
10.6	0	255	241	2	14	36	242
10.7	0	255	241	2	14	70	43
10.8	0	255	241	2	14	105	131
10.9	0	255	241	2	14	139	32
11.0	0	255	241	2	14	173	0	3752
11.1	0	255	241	2	14	207	217
11.2	0	255	241	2	14	242	80
11.3	0	255	241	2	15	20	195
11.4	0	255	241	2	15	54	39
11.5	0	255	241	2	15	88	131
11.6	0	255	241	2	15	123	86
11.7	0	255	241	2	15	157	49
11.8	0	255	241	2	15	191	213
11.9	0	255	241	2	15	225	180
12.0	0	255	241	2	16	4	119	3996

Arduino Code

Code Block

/*
 * Encoder on A2, A3 
 * Button on A1
 * MAX 485: 5v to DE, D8 to DI.  A and B to A and B of the treadmill controller
 * TM1637 display clock on 2, data on 3
 * Short out the middle "safety key" pins 
 * Take power from one of the treadmill controller pins (which one?)
 * Treadmill header has 8 pins (left to right, latch at the bottom):
 * 1 - 12v
 * 2 - 12v
 * 3 - A or B?
 * 4 - Safety switch
 * 5 - Safety switch
 * 6 - A or B?
 * 7 - Ground
 * 8 - Ground
*/




#include <AltSoftSerial.h>
//https://www.pjrc.com/teensy/td_libs_AltSoftSerial.html

#include <SimpleTimer.h>
//https://github.com/jfturcot/SimpleTimer

#include <RotaryEncoder.h>
//http://www.mathertel.de/Arduino/RotaryEncoderLibrary.aspx
//https://github.com/mathertel/RotaryEncoder

#include "OneButton.h"
//https://github.com/mathertel/OneButton

#include <TM1637Display.h>
//https://github.com/avishorp/TM1637

#include <EEPROMex.h>
//https://github.com/thijse/Arduino-EEPROMEx

const int encoderButton = A1;
const int encoderA = A2;
const int encoderB = A3;
const int dispClock = 2; //D2
const int dispData = 3; //D3


AltSoftSerial ss;
SimpleTimer timer;
OneButton encoderButt(encoderButton, true);
RotaryEncoder encoder(A2, A3);
TM1637Display display1(dispClock, dispData);

bool halt = true;
int setSpeed = 0;
int curSpeed = 0; //ramp this up until it reaches the set speed
int savedSpeed = 0;
const int speedCount = 123;

const byte b1[] = {0,0,0,0,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,6,6,6,6,6,6,6,7,7,7,7,7,7,7,7,8,8,8,8,8,8,8,9,9,9,9,9,9,9,9,10,10,10,10,10,10,10,11,11,11,11,11,11,11,12,12,12,12,12,12,12,12,13,13,13,13,13,13,13,14,14,14,14,14,14,14,14,15,15,15,15,15,15,15,16,16,16,16,16,16,16,16};
const byte b2[] = {0,161,195,230,8,42,76,111,145,179,213,248,26,60,94,129,163,197,231,10,44,78,112,147,181,215,249,28,62,96,130,165,199,233,11,46,80,114,148,183,217,251,29,64,98,132,166,200,235,13,47,81,116,150,184,218,253,31,65,99,134,164,202,236,15,49,83,117,152,186,220,254,33,67,101,135,170,204,238,16,51,85,119,153,188,222,0,34,101,103,137,171,206,240,18,52,87,121,155,173,224,2,36,70,105,139,173,207,242,20,54,88,123,157,191,225,4,20,54,88,123,157,191,225};
const byte b3[] = {221,16,201,186,144,116,105,188,33,197,216,18,156,188,101,79,171,182,82,43,11,210,8,154,186,99,250,96,132,229,70,87,142,23,64,51,212,48,87,130,38,194,136,186,94,57,221,121,172,63,219,60,79,236,117,172,189,135,230,2,54,175,118,86,112,234,51,19,158,122,103,131,132,93,125,222,20,9,237,132,81,76,168,118,5,220,105,141,161,69,139,127,49,235,188,156,116,237,78,110,92,210,242,43,131,32,0,217,80,195,39,131,86,49,213,180,119,195,39,131,86,49,213,180};
const int sfm[] = {0,262,314,366,418,471,523,575,628,680,732,785,837,889,941,994,1046,1098,1151,1203,1255,1308,1360,1412,1464,1517,1569,1621,1674,1726,1778,1831,1883,1935,1987,2040,2092,2144,2197,2249,2301,2355,2406,2458,2510,2563,2615,2667,2721,2772,2824,2878,2929,2981,3033,3087,3138,3190,3244,3295,3347,3401,3453,3504,3556,3610,3661,3713,3767,3818,3870,3924,3976,4027,4079,4133,4184,4236,4290,4342,4393,4447,4499,4550,4602,4656,4708,4759,4813,4865,4916,4970,5022,5074,5125,5179,5231,5282,5336,5388,5440,5493,5545,5597,5648,5702,5754,5805,5859,5911,5963,6016,6068,6120,6171,6225,6277,6329,6382,6434,6486,6539,6591,6643};

//eeprom memory locations
const int memAddress = 20;
const int memBase = 350;


void setup() {
  //interrupts for encoder
  PCICR |= (1 << PCIE1);    // This enables Pin Change Interrupt 1 that covers the Analog input pins or Port C.
  PCMSK1 |= (1 << PCINT10) | (1 << PCINT11);  // This enables the interrupt for pin 2 and 3 of Port C.
  //Serial.begin(9600);
  ss.begin(9600);
  timer.setInterval(100, sendSpeedPacket);
  encoderButt.attachClick(startStop);

  // Set Up EEPROM
  EEPROM.setMemPool(memBase, EEPROMSizeNano);

  //Load the stored speed value
  setSpeed = EEPROM.readInt(memAddress);

  display1.setBrightness(2);
  updateDisplay();
}

void loop() {
  // put your main code here, to run repeatedly:
  timer.run();
  encoderButt.tick();
  readEncoder();
  updateDisplay();
}

void sendSpeedPacket() {

  if(halt == true) { //send the stop packet
    ss.write((byte)0);
    ss.write((byte)255);
    ss.write((byte)241);
    ss.write((byte)2);
    ss.write((byte)0);
    ss.write((byte)0);
    ss.write((byte)221);
  }
  else { //send the current speed packet
    ss.write((byte)0);
    ss.write((byte)255);
    ss.write((byte)241);
    ss.write((byte)2);
    ss.write((byte)b1[curSpeed]);
    ss.write((byte)b2[curSpeed]);
    ss.write((byte)b3[curSpeed]);   
  }

  if (halt == true){
    curSpeed = 0;
  }

  if (curSpeed < setSpeed && halt == false) { //this ramps the sent speed up until it hits the set speed
    curSpeed++;
  }
  if (curSpeed > setSpeed && halt == false) { //this immediately reduces the sent speed to the set speed
    curSpeed = setSpeed;
  }

  //Serial.print(halt);
  //Serial.print(" ");
  //Serial.println(curSpeed);
  
}

void startStop () {
  halt = !halt;
  EEPROM.writeInt(memAddress, setSpeed); //save the speed every time the button is pushed... so that on next power up it is not zero
}

void readEncoder() {
  static int pos = 0;

  int newPos = encoder.getPosition();
      if (pos > newPos) {
        setSpeed = setSpeed - 1;
      }
      else if (pos < newPos) {
        setSpeed = setSpeed + 1;
      }
      pos = newPos; //--keep

      setSpeed = constrain(setSpeed, 0, speedCount);


}

ISR(PCINT1_vect) {
  encoder.tick(); // just call tick() to check the state.
}


void updateDisplay() {
  display1.showNumberDecEx(sfm[setSpeed], 0, true);  //Set time should always show on display 1
//  Serial.print("Minutes: ");
//  Serial.print(seconds / 60);
//  Serial.print("Seconds: ");
//  Serial.println(seconds & 60);
}

Example ESP8266 Code

Image Added

https://www.mischianti.org/2020/05/11/interface-arduino-esp8266-esp32-rs-485/

Sample Code for ESP8266 Wemos:

Code Block

#include "Arduino.h"
#include <SoftwareSerial.h>
#include <Ticker.h>

#define SER_RX_PIN            D2  // Serial Receive pin
#define SER_TX_PIN            D3  // Serial Transmit pin
  
//RS485 control
#define SER_CONTROL_PIN       D0 // Transmission set pin
#define SER_TX_VALUE          HIGH
#define SER_RX_VALUE          LOW

  
SoftwareSerial serialPort(SER_RX_PIN, SER_TX_PIN); 
Ticker         ticker;  

int     byteSend;
String  dataReceived;
bool    isDataReceived = false;

bool    halt = true;
int     setSpeed = 0;
int     curSpeed = 0; //ramp this up until it reaches the set speed
//int     savedSpeed = 0;
//const int speedCount = 123;
 
const byte b1[] = {0,0,0,0,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,6,6,6,6,6,6,6,7,7,7,7,7,7,7,7,8,8,8,8,8,8,8,9,9,9,9,9,9,9,9,10,10,10,10,10,10,10,11,11,11,11,11,11,11,12,12,12,12,12,12,12,12,13,13,13,13,13,13,13,14,14,14,14,14,14,14,14,15,15,15,15,15,15,15,16,16,16,16,16,16,16,16};
const byte b2[] = {0,161,195,230,8,42,76,111,145,179,213,248,26,60,94,129,163,197,231,10,44,78,112,147,181,215,249,28,62,96,130,165,199,233,11,46,80,114,148,183,217,251,29,64,98,132,166,200,235,13,47,81,116,150,184,218,253,31,65,99,134,164,202,236,15,49,83,117,152,186,220,254,33,67,101,135,170,204,238,16,51,85,119,153,188,222,0,34,101,103,137,171,206,240,18,52,87,121,155,173,224,2,36,70,105,139,173,207,242,20,54,88,123,157,191,225,4,20,54,88,123,157,191,225};
const byte b3[] = {221,16,201,186,144,116,105,188,33,197,216,18,156,188,101,79,171,182,82,43,11,210,8,154,186,99,250,96,132,229,70,87,142,23,64,51,212,48,87,130,38,194,136,186,94,57,221,121,172,63,219,60,79,236,117,172,189,135,230,2,54,175,118,86,112,234,51,19,158,122,103,131,132,93,125,222,20,9,237,132,81,76,168,118,5,220,105,141,161,69,139,127,49,235,188,156,116,237,78,110,92,210,242,43,131,32,0,217,80,195,39,131,86,49,213,180,119,195,39,131,86,49,213,180}; 

  
void setup()  {
  Serial.begin(115200);

  //initialize RS485 
  pinMode(SER_CONTROL_PIN, OUTPUT);
  digitalWrite(SER_CONTROL_PIN, SER_RX_VALUE);
  serialPort.begin(9600);
  
  ticker.attach_ms(15,sendSpeedPacket);
  
}


void loop() {

//    setSpeed = 0;
//    delay(30000);
//    setSpeed = 1;
//    delay(30000);
//    setSpeed = 10;
//    delay(30000);
//    
//    setSpeed = 1;
    delay(30000);
    setSpeed = 5;
//    delay(30000);
//    setSpeed = 12;
    delay(30000);
    halt=true;
  
}

void processSerial(){
  processReceived();
  sendSpeedPacket();
}

void processReceived(){
  
    digitalWrite(SER_CONTROL_PIN, SER_RX_VALUE);// Init receive
  
    if (serialPort.available()){
        dataReceived = serialPort.readString();
        Serial.print("Data received ");
        Serial.println(dataReceived);    
    }

}

void sendSpeedPacket() {
 
  if(halt == true) { //send the stop packet
    serialPort.write((byte)0);
    serialPort.write((byte)255);
    serialPort.write((byte)241);
    serialPort.write((byte)2);
    serialPort.write((byte)0);
    serialPort.write((byte)0);
    serialPort.write((byte)221);
  }
  else { //send the current speed packet
    serialPort.write((byte)0);
    serialPort.write((byte)255);
    serialPort.write((byte)241);
    serialPort.write((byte)2);
    serialPort.write((byte)b1[curSpeed]);
    serialPort.write((byte)b2[curSpeed]);
    serialPort.write((byte)b3[curSpeed]);  
  }
 
  if (halt == true){
    curSpeed = 0;
  }
 
  if (curSpeed < setSpeed && halt == false) { //this ramps the sent speed up until it hits the set speed
    curSpeed++;
  }
  if (curSpeed > setSpeed && halt == false) { //this immediately reduces the sent speed to the set speed
    curSpeed = setSpeed;
  }
 
  Serial.print(halt);
  Serial.print(" ");
  Serial.println(curSpeed);
   
}

Code Block

$ sort tmp.txt | uniq -c 
 411 
   4 +1
   4 +2
   1 01 1a fe df 00 fd ce 1a ec fe 3a ac fe
   1 01 1a fe df 00 fd ce 1a ec fe 5e f4 fd
   1 01 1a fe df 00 fd ce 1a ec fe 76 2c fe
   2 01 1a fe df 00 fd ce 1a ec fe 7a b4 fc
   1 01 1a fe df 00 fd ce 1a ec fe e6 d4 fc
   2 01 1a fe df 00 fd f2 1a ec fe fe fa ff
   1 01 1a fe df 00 fd f6 1a ec fe fe b6 fe
   2 01 1a fe df 00 fd fa 1a ec fe fe a6 fe
   4 01 1a fe df 00 fd fe 1a ec fe fe ea ff
  19 01 26 f6 ff af 1f 00 fd ce 26 fc 76 fe
   1 01 26 f6 ff af 1f 00 fd f6 26 fc aa ff
   1 01 26 f6 ff af 1f 00 fd fa 26 fc 82 fe
  10 01 26 f6 ff af 1f 00 fd fe 26 fc 9a fe
  18 01 3a f6 ff bd be 00 fd ce 3a fc ce ff
   5 01 3a f6 ff bd be 00 fd f6 3a fc 12 fe
  10 01 3a f6 ff bd be 00 fd fe 3a fc 22 ff
   5 01 3a f6 ff ff 45 00 fd f2 3a fc 0a fe
   6 01 3a f6 ff ff 45 00 fd fa 3a fc 3a ff
   1 01 3a f6 ff ff 45 00 fd fe 3a fc 22 ff
   1 01 0d fe df 00 fd ce 1a ec fe
   1 01 13 f6 ff af 1f 00 fd ce 26 fc 76 fe
   1 01 1a fe df 00 fd ce 1a ec fe 72
  35 01 1a fe df 00 fd fe 1a ec fe fe ea ff
  15 01 1a fe df 00 fd fe 1a ec fe fe ea ff 
   4 01 26 f6 ff af 1f 00 fd ce 26 fc 76 fe
   5 01 3a f6 ff bd be 00 fd ce 3a fc ce ff
 199 01 3a f6 ff ff 45 00 fd fe 3a fc 22 ff
  41 01 3a f6 ff ff 45 00 fd fe 3a fc 22 ff 
   1 01 3a f6 ff ff 45 f4 fe 3a fc 22 ff
   1 01 3e ff 1f 00 fd fe 3e fe 7e fe
   1 01 be f6 ff 0b c2 00 fd fe be fc a6 fe

Byte Stream

Code Block

title	Bytes
collapse	true

01 3a f6 ff bd be 00 fd ce 3a fc ce

...

01 26 f6 ff af 1f 00 fd ce 26 fc 76 fe

01 3a f6 ff bd be 00 fd ce 3a fc ce ff

01 13 f6 ff af 1f 00 fd ce 26 fc 76 fe

01 0d fe df 00 fd ce 1a ec fe

01 3e ff 1f 00 fd fe 3e fe 7e fe

01 be f6 ff 0b c2 00 fd fe be fc a6 fe

+1

01 1a fe df 00 fd fe 1a ec fe fe ea ff