ground planes and isolation

artag

I got my sensors today. First impressions good 🙂

I want to use a Craft to make a sensor very like a Bar, but flexible enough to be built into a sleeve or a pad on the forearm. I plan to do this by using a number of lines of a flexible conductor, oversewed to make electrodes that don't touch.

Before In start building, I've got some questions :

Is the width of the electrode important ? Would I be best using a flat braid or would a wire be sufficient ?

There is plenty of residual capacitance as all electrodes have the skin of the arm behind them. I assume Trill does some sort of calibration - will that be sufficient to ignore this ? Or should I try to space the electrodes away from the supporting arm, or place a reference plane between arm and electrodes ?

giuliomoro

We have made some flexible PCBs in the shape of a slider to connect to the Craft, and in that case the PCB was very similar to that of the BAR. Helen Leigh has attached Trill Craft to some flex PCB she wore around her neck

artag Is the width of the electrode important ? Would I be best using a flat braid or would a wire be sufficient ?

either should be fine.

artag I assume Trill does some sort of calibration - will that be sufficient to ignore this ?

when used in differential mode (default for Craft), the sensor is calibrated when the program starts: the baseline capacitance measured at that point is subtracted from further readings. Make sure you check out this page: you will surely need it for building tour custom device.

In your case the challenge is about ensuring the baseline capacitance does not change much as the conductor moves in the proximity of the wrist's skin. You may have to experiment a bit to find the best fit for your application.