EEG stuff part 1

I heard about a cure for insomnia where you use biofeedback to train yourself to have more delta brainwaves, which are associated with deep sleep. This was on the Joe Rogan Experience, which means it has to be legit. Since then I’ve made some attempts at an EEG like the OpenEEG so I can play with different forms of neurobiofeedback.

There are a variety of biological electric potentials which can be measured for biofeedback. ECG signals are higher amplitude than EEG ones and can be used to measure heart rate and health. EMG is higher frequency and measures the signals causing muscle contraction. I’m starting with ECG because it has a very clear shape and large amplitude, which will help with debugging.

To make things even easier, I started by ordering a dev board for a 32bit ADC on digikey (https://www.digikey.de/en/product-highlight/t/texas-instruments/ads1262-adc).

32 bits! That gives you minimum voltage increments of less than a nV! EEG potentials are a bit less then uV so this should make it easy.

Again, just to get something easy working, I installed windows so I could use the included software. As electrodes, at first I just tried a pair of wires soldered to silver disks as leads, which had massive amounts of interference. This was measured across my chest, with professional electrode jelly. There was always a ton of 60Hz signal. Then I moved to good shielded coax and connected my right leg to the intermediate voltage (1.6V) to stay within the voltage range. Articles mentioned grounding or driving the shields, both of which made the signal quality worse.

R and T components pretty visible, some drift and plenty of 60Hz.

And it worked! I got clear ECG traces (with a decent amount of 60Hz noise) and went to get something working on linux. In the meantime I broke the motherboard for the ADC, so I had to set up something to power it and get data off of it.

To be continued…

Author: Garth Whelan

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