[Senior Design] PCB Assembly, Testing and Debugging

Here’s a long-overdue progress update on our senior design project. A semester-end post will soon follow. Since the last post, a lot has happened:

The PCB and parts came in…

IMAG0405

…There was some soldering and assembly…

We hacked together an alternative 3.5mm jack (which has since been glued in place), since the original part had too long of a lead time. It is raised up, since this alternative part required rotating the jack compared to the original part, but the electrode cable housing needed a clearance to be plugged in.

Testing and verification of our modules began and has been long underway…

IMAG0414

Above: Power circuitry noise at no load. The switching supply is in power-saving mode here. The noise we see is purely from the resolution of the scope being used. This was verified by plugging a power supply directly into the scope and reading about 14mVpp.

IMAG0417

Above: Power circuitry noise at near-max load. Switching seen at 1 MHz (as designed) but the peak-to-peak noise from the repetitive transients are much higher than designed and simulated for. To be honest, I was pretty unskilled at using oscilloscopes at this point, so I really could have been missing some other key details when I captured this.

Our current strategy is to try to work around this, since we do not have time to spin a new board and the switching controller has pins that are two small to put something in series with to attenuate the noise. We may attempt to add some additional bulk capacitors.

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