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iliasam edited this page Oct 16, 2021 · 6 revisions

Welcome to the Laser_tape_reverse_engineering wiki! This project describes my work about reverse engineering electronics (laser rangefinder module) of a cheap "X-40" laser tape measure.
I create my own firmware that allow to use this module for DIY purposes.
Supported module types are: "512A" and "701A", "703A". UPD 11/2019: Attention: It was found that newer "x-40" laser tape measures come with "M88B" modules. Marking is "88B" at the PCB near MCU. That modules are based on STM32F0 MCU (it has QFN-32 package). That modules are not supported by my firmware!
Module dimensions: 25x13x50 mm.

Big article in Russian: https://habr.com/post/327642/
Google translated: Link.
Another project page: https://hackaday.io/project/25515-cheap-laser-tape-measure-reverse-engineering

Steps that I have done:

  • Fully reverse engineered schematic of the laser tape measure.
  • Captured data packets at I2C bus with logic analyzer.
  • Decoded that packets and get values of laser modulation frequencies.
  • Create my own firmware that captures low frequency signal and send it to PC.
  • Create my own firmware that captures signal and processing if using Goertzel algorithm. Phase difference results are send to the PC.
  • Main result: Create my own firmware ("Firmware_dist_calculation_fast") that calculates distance to the object.
  • Write C# PC utilities to process and show results.

Video (testing rangefinder module): https://youtu.be/bJaUrZ7ZMj4

Main parts of the laser rangefinder module are STM32F100C8T6 MCU, Si5351 dual PLL, APD (unknown type), laser diode, power sources.
Laser tape measure structure schematic:

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