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A project log for RISE

Solar powered Bluetooth Low Energy window blinds

tiit-rtsepTiit Rätsep 01/27/2015 at 17:310 Comments

Today we found out that a capacitive touch button right next to a big motor might not be a good idea. Actually we were worried about that for a long time but the only way to be sure way to actually test it. The main problem is that we need to detect touch from about 6 mm away through two layers of plastic. And the other side of the PCB is right against the back of a DC motor. We are using an Atmel touch button IC that we tried on a prototype and it seemed to mostly work but had some spurious touch events. The new PCB has a much better layout for the touch sensor and without the motor it works beautifully. The problem is that this Atmel chip has a feature for stuck on state detection. And when we turn on the motor the button senses that as an on condition and if the motor runs long enough it recalibrates. After recalibration the touch no longer works and we have to reset the device. We could force it to periodically recalibrate to fix this but then we'd have the problem that sometimes the user is touching the button just as it recalibrates and that would break it for this one calibration cycle. We don't want to risk this at the moment and decided to try a mechanical button.

We had some problems with the controller resetting randomly but that seems to come from using a lab supply instead of a real battery. Probably the long wires and current limited source cause a voltage drop that resets the controller whenever we have a large enough current spike. We might add a tall electrolytic cap in there somewhere as we have some room next to the motor inside the case.

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