The communication between LCD and motor controller is a simple serial TTL-level connection with a baudrate of 9600. For each direction (motor to LCD / LCD to motor), There is one data message/packet format, that is repeated multiple times per second.
Example message:
43 00 01 51 51 00 07 07 F4
Send frequency: 8 per second Content:
| Byte No. | example | description |
|---|---|---|
| 1 | 0x43 | Start-Byte |
| 2 | 0x00 | Battery level |
| 3 | 0x01 | Motor status flags |
| 4 | 0x51 | Pedal torque-sensor "tara" value |
| 5 | 0x51 | Pedal torque-sensor actual value |
| 6 | 0x00 | Error code |
| 7 | 0x07 | Speedsensor (LOW part of 16bit int) |
| 8 | 0x07 | Speedsensor (HIGH part of 16bit int) |
| 9 | 0xF4 | Checksum |
Example message:
59 40 00 1C 00 1B D0
Send frequency: 15 per second
Content:
| Byte No. | example | description |
|---|---|---|
| 1 | 0x59 | Start-Byte |
| 2 | 0x40 | Motor control flags |
| 3 | 0x00 | unused |
| 4 | 0x1C | Wheel size |
| 5 | 0x00 | unknown, probably unused by LCD |
| 6 | 0x1B | Maximum speed |
| 7 | 0xD0 | Checksum |
| Bit | description |
|---|---|
| #0 | low voltage |
| #1 | unknown |
| #2 | motor running (if not in speed limit) |
| #3 | PAS status / pedals spinning |
| Bit | description |
|---|---|
| #0 | headlight |
| #1 | assist level 2 |
| #2 | assist level 3 |
| #3 | assist level 4 |
| #4 | assist off |
| #5 | 6kph mode |
| #6 | assist level 1 |
| #7 | hidden/unused assist level below level 1 |
Wheel size in inch, e.g. 0x1C in decimal are 28inch
Controller probably only uses values between 6 and 29 inch.
Firmware default (without LCD) is 0x1a / 26 inch.
Speed in kph, e.g. 0x1B in decimal is 27kph
If a value below 0x0e (14kph) is sent to the controller, it uses the default value 0x19 (25kph) instead.
The torque sensor is read when motor is powered on.
This value is used as reference to detect if force is applied to the pedals.
Value can change a little bit after a stop.
This is the current value of the sensor.
To get the applied force, you have to subtract the first byte / "tara" value.
The exact conversion factor has to be tested.
The value increases by about 2.7 for every kg added load on a pedal at a pedal arm length of 17cm length.
That should be about 3.6 Nm per unit on the axis?
Calculated based on the setting in the EEPROM
| value | voltage (36V) | display |
|---|---|---|
| 00 | ≈33V | red and blinking |
| 01 | ≈34V | 1 red bar |
| 02-09 | green range | |
| 0A | >=38V | full |
| Though the motor sends values above 0A, the LCD doesn't show any difference, just green and full. |
The speed is basically a 16bit integer that contains the time between two trigger events of the speed sensor = one rotation.
Each unit stands for about 2.04 ms time.
Example calculation:
28 inch wheel = 2.24 m per rotation
Value: "89 01" = 0x0189 = 393 units
Time per ration: 393 units * 2.04 ms = 801.72 ms
Rotations per second: 1000 ms / 801.72 ms = 1.247 rotations/second
Speed: 1.247 rotations/second * 2.24 m per rotation = 2.79 m/s * 3.6 = 10kph
When standing still, the motor sends the maximum value "07 07" (0x0707 / 1799), so like it would be ≈3.6 seconds.
The LCD already ignores values above 1750 / 0x6d6.
| code | description |
|---|---|
| 08 | undervoltage |
The checksum is basically the sum of previous bytes as 8bit unsigned integer.
See "1 byte checksum" described here: https://www.lammertbies.nl/comm/info/crc-calculation.html