DIY strength analyzer for climbing.
Device used: Wemos C3 Mini.
Flash micropython.
esptool.py --chip esp32c3 --port /dev/ttyACM0 --baud 1000000 write_flash -z 0x0 LOLIN_C3_MINI-20220618-v1.19.1.bin
Install needed libs:
mpremote mip install aioble
mpremote mip install aioble-server
Load code:
mpremote cp hx711_gpio.py :
mpremote cp main.py :
Reset device and connect from the mobile App.
Each cell should be calibrated to give accurate results.
There are two values to be calibrated, scale and offset.
To give a weight in kg the device makes a raw measurement and then uses the formula: (raw_meas - offset) * scale.
To calibrate the device we can use the app progressor_calibrate.py:
pipenv install
pipenv run progressor_calibrate.py
And follow the instructions.
It will ask to put two different known weights on the device and put that value in this app. With those two measures it will calculate the scale and offset, and store it for future uses.
This element will be placed between the anchor and our hangboard (or the hold we use) to measure the force.
I bought this one in Amazon.
I guess any brand selling PSD-S1 will work.
I chose 300kg because 100kg is not enough and 2000kg will have a bigger error.
To connect the load cell to the WemosC3 we need an ADC (analog-digital converter).
HX711 is an unexpensive ADC specifically designed to weight scales.
It should be configured to do 80 SPS (samplings per second), by default it is normally configured to do 10.
Not all boards allow to change from 10 to 80 SPS. For example this one needs a modification, which is complicated (check here if you need to do that modification).
It is better to buy a board ready to be changed to 80 SPS, like this one.
To connect the WemosC3 to the HX711:
3v3 - Vcc
GPIO - DT
GPIO - SCK
GPIO - GND
To connect the load cell to the HX711:
Red - E+
Black - E-
White - A-
Green - A+
We can use the official Progressor mobile app to get the readings.
The "Tare" button in the phone app does not send any command to the device, it just make the calibration internally and save the results for future connections.