HealthyPi 5

An extensible, open-source sensor platform for biosignal acquisition

Oct 11, 2023

Project update 8 of 11

Production Has Resumed

by Ashwin W

We have had an adventurous journey the last few weeks, but we are happy to report that we are back on track and production of the HealthyPi 5 has resumed. We have already started production of the main boards and the add-on boards for the complete kit version. Many of you have been asking us about the status of the project, and we sincerely apologize for the delay. We will try to explain the reasons for the delay in this update.

EMI/EMC Testing

The main factor behind the delay was the Electromagnetic Interference (EMI) and Electromagnetic Compatibility (EMC) testing. EMI/EMC testing and getting time slots to access the labs was hard, apparently there’s quite lot of demand in India currently and a small supply of quality labs. We had to do this testing to make sure the device does not interfere with other devices and to make sure the device is not affected by other devices or poses any potential safety hazards. This is a mandatory test for most electronic devices and is a prerequisite for CE conformity (especially for shipment to the EU and UK).

Since the funds from Crowd Supply were delayed, we were unable to start testing until August and the results were not good. The Radiated emissions(RE) coming out of the device were above the allowed limit of 40 dB according to the CISPR 32 Standard which dictates the allowable radiation. Below are plots of the the horizontal and vertical sweeps of radiated emissions. The red line is the allowable limit and blue peaks are the measured values. Those spikes from about 167 MHz to 260 MHz are the ones causing the problem.

Instead of trying to rework the prototypes to pass the test by adding on a few ferrites or inductors, we decided to tear up the previous layout and redo the board layout entirely to make sure the production devices do not have any unintended effects when in customer hands. This approach worked well for us. Below is a picture of the latest set of boards we’ve tested. The key change is that all boards are now four-layer PCBs with dedicated ground planes for the top and bottom layers that act as shields. Although some may disagree, we belive this approach gave us the best solution. The lesson learned: "We should have thought about ground return paths from the the beginning of the design process". Instead, we were more carried away by features and such and overlooked some obvious issues. However, there have been NO changes to the functionality of the device; the device is still the same as the one we had originally planned to ship.

Below are the results of the EMI/EMC test for the latest design. As you can see, the results are much better and are well within the limits. The first set of plots are for the horizontal and vertical sweeps from 30 MHz to 200 MHz, and the second set are the horizontal and vertical sweeps from 200 MHz to 1000 MHz. The 1 GHz - 6 GHz tests are not shown here as they weren’t a problem earlier either.

We have yet to receive out final certified test reports, but they will contain the same data as above and we should receive them in the next couple of weeks.

HealthyPi 5 Production Has Resumed

Now that we have the results of the testing, and are only waiting for the reports to be official, production has resumed full speed and we are expecting to have the devices ready for shipping as soon as we get the certified test reports. This should happen in the next two weeks.

There has also been considerable progress in the Zephyr-based version of the HealthyPi firmware; we will post an update on that soon. We are also working on the Android app and the desktop app and we will post updates on those as well. For those who are not aware of this separate set of firmware with Zephyr, please read our earlier update. The Zephyr repo is also available to the public on Github and we welcome contributions and feedback. All future development will be made on the public repo only.

We sincerely apologize for the delay and mistakes made. We are working hard (and carefully) to make sure we do not have any more hold-ups. We do not see anything at this time that could cause any further delays.

Thank you for your patience and continued support.

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