GLM20 - Interface USB/Serial Following the forum instructions, I've done several communication tests in the past with the GLM20. But my tests failed. I got frustrated and stopped.
Rereading all the threads, I realized that the PRL15 circuit board was identical to the GLM20. (Thanks RTV). I thought - it has to work!
If the RTV colleague did it, I think I can too.
Yesterday, doing more tests using an oscilloscope to monitor the waveform of the serial signal on pin P58/P59, I received a response to a command. But the received signal was truncated. I realized that the low level of the signal was at 1V, inadequate for reception.
After that, I built a circuit using resistors, schottky diode, a 74HC00 chip and managed to correctly read the received data.
Today thinking happily about being able to read the data, I built another simpler circuit, with a 74HC07 chip. Why HC chip? Because it works with 3.3V! Do not use an ordinary 7407.
This is the circuit built by me. It's the first one that worked with my tests. I checked with the oscilloscope and the signal is fine. We can then make other improvements if necessary.
Usage sequence:
1) press the power button on the GLM20
2) Press the reset button SW2 (display turns off)
3) Press the SW1 button to activate the communication (backlight on)
4) Run a terminal program connected to the USB of the CP2102 module - 9600 Bps 8N1.
5) Send the command and you will see the results.
To do later
- Connect with an Arduino, Raspberry PICO or ESP32
- Make a Golang program to run on a Windows/Linux/MAC
Thanks RTV - instructions to use Realterm:
https://www.eevblog.com/forum/projects/hacking-the-bosch-glm-20-laser-measuring-tape/msg1450020/#msg1450020Display as = HEX SPACE OR ANSI