ThinkPulse Active Electrodes on Cyton:Excellent Impedance but Persistent Near-Railed / Railed Signal

Hello OpenBCI team,

I’m writing regarding a persistent issue using ThinkPulse active EEG electrodes with a Cyton board.

Despite correct placement and consistently excellent impedance values (typically 4–10 kΩ across channels), the EEG signal is almost always flagged as “Near Railed” or “Railed,” with rail percentages frequently exceeding 80–100%. The waveform appears compressed/clipped rather than physiological, and uVrms values are abnormally high.

This occurs across multiple channels and sessions and does not improve with repositioning, re-referencing, or impedance optimization. The contradiction between low impedance and severe rail saturation suggests an input range / gain mismatch rather than a contact or noise issue.

Given that ThinkPulse electrodes are actively amplified and Cyton already operates at a high front-end gain, it appears the combined gain is saturating the ADC input. However, this limitation is not clearly communicated in the ThinkPulse documentation or purchasing guidance, where the system is presented as compatible and relatively plug-and-play.

At this price point, I expected improved signal quality and reduced setup complexity compared to passive electrodes, not persistent rail saturation under normal conditions.

Could you please clarify:

Whether Cyton gain must be reduced or modified specifically for ThinkPulse electrodes

Whether additional attenuation or configuration is required

Whether this behavior is a known limitation of the Cyton + ThinkPulse combination

I’ve attached a screenshot showing excellent impedances alongside severe rail saturation to illustrate the issue.

Thank you for your help and clarification.

Best regards,