The S×3 is very close to being ready to plug in to the Raspberry Pis and collecting data!

Current state

  • All have been bootloaded and are programmable via USB on my windows 10 machine.
  • A python script has been written to accept data over USB and print to file via stdout.
  • Alex has assisted in setting up scripts (python and shell) and my own AWS server to collect the sensor data from the RPis

What’s left?

Calibration of the analogue sensors is needed

  • Temperature
    • Currently the function (Steinhart-Hart Equation) which transforms the ADC thermistor resistances to temperature is giving ~37°C. I have a feeling this is incorrect…
    • This slight discrepancy is possibly due to incorrect coefficients being used in the equation, I assumed the values from the Vishay datasheet would give the correct temperature.
    • Potentially it’s a linear offset (due to input impedance/voltage characteristics), but testing is needed (I’ve moved onto sound for now)
  • Sound
    • This post in electronics stack exchange explains how to convert from voltage levels (or 10 bit ADC values) to a useful sound pressure level (SPL) in dB.
    • Gain will need to be tuned for optimal sensitivity. If gain is too high the Signal to Noise Ratio (SNR) is too low, and no valuable sound info is measured.
    • I have removed the resistors for gain and replaced them with a 1 MΩ trim potentiometer (pot) to test the effects of gain.

Control Neopixel

  • Using blink(1)
    • blink(1) is a USB controlled RGB LED using the attiny85 and a neopixel. This is very close to what we are doing, and very importantly, the project is open source with a very well documented public github repo.
    • The two however are not compatible and there are a lot of things to consider. See this post to get an idea.
    • the biggest challenge will be adapting firmware to suit our needs/hardware.
  • Preset control via arduino IDE
    • I can already control the NP via terminal using preset conditions.
    • An odd error occurs

Test server upload

  • Alex has adapted code for the badges to work with the S×3