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By ozdan
#203160
Hello.

I am seeking some broad advice on the design (i.e. selection of components) of a piece of wearable technology that I would like to make.

Aim - I want to measure the acceleration of the wrist when throwing a ball.

Constraints
- The measurement device needs to be small and battery powered
- I want to wirelessly transmit the measurements
- I need to capture peak acceleration (which is well above 20 g)

Capacity
- I can solder and assemble hardware
- I have Arduino experience
- I can 3D print an enclosure
- I can learn new skills
- If I can get the data to a PC via Bluetooth, I'll be able to handle the subsequent processing

Questions
1. The only 3-axis accelerometer I can find here that goes above 16 g is the ADXL377. Is this suitable, are there better choices?
2. To capture the signals from the accelerometer breakout board and transmit them via WIFI/BLE, I was looking for a small form factor option like the "ESP32 Thing" (although it appears that it doesn't handle analog inputs when using Arduino). Is there a better choice?
3. Will I be able to transmit 3 channels of data at 100 Hz?

Thanks in advance, Dan
#203183
Hi Dan,

That is a neat project and I think we have a couple of options that will work for your microcontroller/transmitter. I will answer your questions below:
  1. That is pretty much correct. We do have this LIS331 Breakout that can be configured to +/-24g but that may not be a large enough range for your project.
  2. The ESP32 Thing could work for this project. The ESP32 Arduino Core does have some analog functionality and you can do analogRead(), just not analogWrite(). That GitHub repository linked above will have more information regarding reading analog inputs. This project example using the Espressif IDF might be helpful for getting started with that code. Another option would be to use the SparkFun Pro nRF52840 Mini Dev Board. To learn more about this board, I would recommend reading our Hookup Guide and the two programming guides linked in that tutorial.
  3. A short answer is yes, you can. There are some mitigating factors regarding your Bluetooth transmission speed but both Bluetooth 4.2 (on the ESP32) and Bluetooth 5 (on the Pro nRF52840) should be able of handling sending data from the ADXL337 at that rate.
I hope this helps you get the right parts for your project.