One more measurement feature that I added to the main unit is an electroencephalogram (EEG) module. The EEG module is mounted on the helmet and uses two active electrodes placed mounted on the sides of the helmet so that they touch the head skin above the ears and one common mode sense electrode mounted on the front inside the helmet, so that it touches the forehead. The common mode settling time after the helmet is placed on the head is about 2-3 minutes, so any meaningful EEG measurements need to wait at least 3 minutes before they start. This is not an issue for sports applications since after these 3 minutes the EEG system is continuously functional for the entire length of the sports activity.
The power supply is provided by the main unit, and the electrodes wires are routed through the inside of the helmet to the forehead and the two locations above the ears. The output of the EEG module is routed to the Arduino nano module inside the main module, where the signal is sampled by an analog-to-digital converter and then encoded to the format needed to be transmitted through the GSM modem.
I will post a video with the displayed waveform in a future update.
That is it for now; I will come back with new updates as I get more work done.