Electrodes & Pinout
Electrode connections
ardEEG has three kinds of electrode inputs.
| Input | Count | Electrode | Purpose |
|---|---|---|---|
| Channels 1–8 | 8 | Dry or wet Ag/AgCl, in the cap | Each channel measures the voltage between its electrode and the reference |
| Reference | 1 | Ear clip on one earlobe | The common 0 µV point that all 8 channels are measured against |
| Bias | 1 | Ear clip on the other earlobe | Actively drives the body to cancel common-mode noise such as 50/60 Hz mains hum |
The electrode header is a standard 2.54 mm pin header, so most EEG cables with 2.54 mm (0.1") female connectors fit. See Cap.
The reference and bias clips matter most. A loose ear clip makes every channel noisy at once. Clean the earlobes and make sure both clips sit firmly.
Suggested montage
These 8 positions spread across the front, centre, sides and back of the head:
| Position | Area | Good for |
|---|---|---|
| F7, F8 | Front left and right, side | Eye movement, frontal activity |
| Fz | Front centre | Blinks, attention; used for the example recordings |
| C3, C4 | Centre left and right | Motor activity (hands) |
| T5, T6 | Back left and right, side | Temporal activity |
| Pz | Back centre, top | Alpha rhythm |
Assign them to channels 1–8 in any order, and keep a note of which channel went where.
Arduino pinout
The shield uses only these Arduino pins, plus power and ground:
| Arduino pin | Signal |
|---|---|
| D13 | SPI clock (SCK) |
| D12 | SPI MISO (data from the ADS1299) |
| D11 | SPI MOSI (data to the ADS1299) |
| D10 | Chip select |
| D7 | DRDY: data ready from the ADS1299 |
All other pins are free for your own sensors, buttons or outputs.
DRDY goes low each time a new sample is ready (250 times per second). The sketch waits for that edge, then reads 27 bytes over SPI. Details in Specification.