Laser distance meter hack

 ➡ Before you connect any hardware to the LCD bus of the laser distance meter make sure it runs at 3V signal levels! The Arduino Mini by default is not! Solutions are either level converters or, what I did, simply exchange the linear voltage regulator IC1 on the Arduino Mini board to an 3V version.

Running the Arduino Mini at 3V brings also the advantage that you can power the device main board directly from the Arduino Mini. Doing so requires an additional capacitor of at least 1000uF/6.3V connected to the power input (where the battery wires were connected) to buffer any power surge when the device and laser will be switched on.

Next I coded a quick and dirty sketch for a Arduino Mini board. It uses the circular buffer library from https://github.com/rlogiacco/CircularBuffer.

This code reads two frames then sends them via serial interface. It ignores the very first short pulse leading each data byte. The result looks like this:

10 00 C0 00 00 0A 00 02 00 00 05 58 00 00 00 00 00 10 01 C0 00 00 06 00 02 00 00 03 F0 00 00 00 00 00 10 02 C0 00 00 02 00 02 C0 00 C5 70 00 00 40 00 00 10 03 C0 00 00 00 00 42 00 00 07 58 60 00 06 00 00 
10 00 C0 00 00 0A 00 02 00 00 05 58 00 00 00 00 00 10 01 C0 00 00 06 00 02 00 00 03 F0 00 00 00 00 00 10 02 C0 00 00 02 00 06 C0 00 C5 70 00 00 40 00 00 10 03 C0 00 00 00 00 42 00 00 07 50 60 00 06 00 00 
10 00 C0 00 00 0A 00 02 00 00 05 58 00 00 00 00 00 10 01 C0 00 00 06 00 02 00 00 03 F0 00 00 00 00 00 10 02 C0 00 00 02 00 02 C0 00 C5 70 00 00 40 00 00 10 03 C0 00 00 00 00 42 00 00 07 58 60 00 06 00 00

Each 68 bytes frame contains 4 sub-frames of 17 bytes starting with:

10 00 C0
10 01 C0
10 02 C0
10 03 C0

These are command bytes (first bit = 0) while the remaining 14 bytes are LCD data (first bit = 1). This bus is driving the LCD.

2F 34 B1 1E B2 0F 14 A0 94 68 3D 88 88 88 88 60 E3 
10 00 C0 FF FF FF FF FF FF FF FF FF FF FF FF FF FF 10 01 C0 FF FF FF FF FF FF FF FF FF FF FF FF FF FF 10 02 C0 FF FF FF FF FF FF FF FF FF FF FF FF FF FF 10 03 C0 FF FF FF FF FF FF FF FF FF FF FF FF FF FF 
10 00 C0 FF FF FF DF FF FF FF FF FF FF FF FF FF FF 10 01 C0 FF FF FF F7 FF FF FF FF FF FF FF FF FF FF 10 02 C0 FF FF FF FB FF FF FF FF FF FF FF FF FF FF 10 03 C0 FF FF FF F3 FF FF FF FF FF FF FF FF FF FF

First line is configuration data for the LCD driver while the two lines with all byte 0xFF are showing all the LCD segments and symbols that we can see for a short moment on the power on screen.

The following sub-frames are showing all symbols of the lowest LCD line, where the actual measured distance is shown including its unit.

10 00 C0 00 00 00 00 00 00 00 FF FF 00 00 00 00 00
10 01 C0 00 00 00 00 00 00 00 FF FF 00 00 00 00 00
10 02 C0 00 00 00 00 00 00 00 FF FF 00 00 00 00 00
10 03 C0 00 00 00 00 00 00 00 FF FF 00 00 00 00 00

So we can break down the distance look-up process into 2 bytes per sub-frame, 8 bytes in total or 64 bit. The look-up table for each number per digit, sign and unit is available for download below.

Lookup Table LCD Last Line (67.2 KB)

This Arduino code will simply read out the distance and sends via serial interface.

2 thoughts on “Laser distance meter hack

  1. It’s so lucky when my Laser Rangefinder was almost like yours (mine was SW-M40). Due to the different, can you help me point out where are the 3 SPI pins in my board? Thank you very much!
    This is the picture of the board
    https://photos.google.com/share/AF1QipOz-SHu2ons81yMIHJ0usprKw2ipbXHM48_K5_R-fGEPUnDD4OujcCK2X6KtnvRvw/photo/AF1QipPVkwGT-talzFGjLetJ5Vk1fEg8AA3hBGyb_Y5f?key=OUVYaGwxZzBJeENzWmJUaXdWanZDeWxlandCZTRR
    Again, thank you very much! So lucky when I got the laser module same as yours.

    • Looks similar. Can you provide a picture from back side of this board?
      In case you have a oscilloscope probe each pin on the LCD connector to find the SPI signals.

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