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DIY laser rangefinder I bought a TFMini lidar module intending to build a radar-like device, but then I realised that at work we spend a lot of time measuring the length of ERW pipes with measuring tapes. ERW (electrically resistant weld) pipes are 300mm plus in diameter and up to 12m long. They are used in our power plant for ash slurry transportation. It’s difficult to measure ERW pipes accurately. So I decided to create a device to accurately measure the length of pipe sections (to within 1cm) using the TFMini TOF (time-of-flight) laser module. Two varieties are available: the TFMini-S (US$35) and TFMini Plus (US$45); both have a serial interface. But the TFMini Plus has a wider measurement range (10-1200cm compared to 30-1200cm), can take 1000 measurements per second instead of 100 and is rated to operate from -20°C to +60°C rather than 0-60°C. Just placing the TFMini at one end of the pipe and directing it towards the edge plate will give accurate length reading. To increase the precision, I average a few readings. 70 Silicon Chip Both the TFMini-S and TFMini Plus have a viewing angle of 3.4°. Therefore, for long pipes, the aim is crucial to get a correct reading. To aid in this, I have incorporated a visible laser pointer with a push-on button (S2). It’s lined up with the TFMini module so you can see to where it measures. The TFMini works on reflection of invisible laser light from the surface of the object. In case the object does not reflect back or completely absorb or diffuse the incoming laser light, the reading will be erroneous. Such surfaces include water or slanted and highly reflective glass windows. For all other kinds of objects, the light gets reflected, and the measurement is correct. It’s accurate even with moving objects. Besides the TFMini module and laser pointer, my circuit uses an ESP32 microcontroller module, a 128x64 pixel OLED screen, two regulators, two capacitors and a battery. The OLED screen is an I2C device so it’s wired to the ESP32’s D21 and D22 I/O pins (just about any pins on the ESP32 can be used for I2C). As mentioned earlier, the TFMini uses serial, so it’s wired to the second UART on the ESP32. Australia’s electronics magazine A 3.3V low-dropout linear regulator (REG1) provides 3.3V to run the ESP32 and OLED display. The TFMini and the laser diode are supplied with 5V generated from a small boost module that runs off a single Li-ion or LiPo cell, with S1 provided for power switching. For use at my workplace, the device has to be portable so that my team can use it out in the field. That is why I ended up using a single LiPo cell and a boost module. It can also run from two 1.5V cells in series. The only real trick to assembling the unit is making sure that the TFMini and laser pointer are aimed at the same spot. To do this, set up a small object just under 12m away from your testing location, aim the TFMini at it until you get a sensible reading, adjust the laser pointer so that the dot is centred on that object and then fix the laser pointer in place. The ESP32 is programmed using the Arduino IDE. You can download the sketch and all the required libraries from siliconchip.com.au/Shop/6/5753 The libraries used are tfmini.h, Adafruit_GFX.h and Adafruit_SSD1306.h. Bera Somnath, Vindhyanagar, India. ($80) siliconchip.com.au