Mark II Update - September 2020

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We got the second revision of the SJ201 daughterboards delivered in late August. Unlike the first run, these were printed as a double sided PCB, however they still required many components to be hand soldered.

Once assembled, Kevin could flash the firmware and start testing the audio!

Two connected PCBs

SJ201 v0.66 – firmware flashing

Testing the audio – a play by play from Kevin

XMOS and the USB Sound card both come up as USB devices in Windows. The USB Audio Device previously also came up on the last boards. And I just realized I flashed the USB adaptive, instead of the USB/I2S firmware.

List of audio devices in menu

USB audio devices detected from SJ201 v0.66

And we have audio recording! I have 2 sets of mic, I’m using the SPK0641 right now, I marked that on the backside of the board (641) so I’ll know which mic is best.

PCB with Mycroft AI logo

SJ201 v0.66 – backside

I’ll give it a full set of testing later today, playing music and recording. Attached is my voice recording, from about 1 foot away, in a decently quiet room, but there is a fish tank and fan behind me, no music playing.

SJ201 v0.66 – audio input waveform

Another system test passed. The mic recording switch directly turns off the mics. I was talking during this time, then flipped the physical switch, and the mics stopped recording.

Audacity screenshot showing audio waveform with silent break in the middle

Audio input waveform showing hardware cutoff

Moved the switch back to this position, it allows recording. Also, I’m now powered through the 12v. The update I did worked. So far, everything is working. Soldering on the LEDs next and the Raspi Connector.

Close up of PCB with hardware switch

SJ201 v0.66 – hardware cutoff for microphone


Overall we’re very pleased with this new revision. We have addressed many of the problems discovered in the first prototype run, but there are still a few issues to resolve.

First we discovered a problem with the output from the amplifier. An incorrect capacitor was spec’d, and replacing that solved the problem. Fortunately that’s just a value change on the part.

We have also noticed some popping sounds when the audio is routed over I2S from the CM108B soundcard to the XMOS 3510. This doesn’t happen when we don’t use the I2S, but we’ve decided we need to simplify the data path. Fortunately XMOS came through on a firmware update and we can reverse the data path to be XMOS → soundcard, which will simplify the design and avoid this issue altogether. We’re testing that now.


SJ230 – laser-cut enclosure for prototypes

For development purposes, we have created a relatively simple laser-cut enclosure with a 3D printed acoustic chamber. This provides a quick case for our development team while we move into the next phase of testing.

Laser cut enclosure for the Mark II prototypes

Once we have cut a few and verified the design, we’ll upload the CAD files to the Mark II hardware repo so that anyone playing from home can get up and running quickly whilst keeping your components safe.


What’s next?

Our focus at the moment is ensuring that the SJ201 meets all of our hardware requirements and getting an SJ201 prototype out to everyone in our team. Once we are confident that the hardware itself is solid, then we can start thoroughly testing running Mycroft on this new hardware.

We’re also looking ahead at the third PCB print run. The next revision will be a fully assembled PCB from the board house.


Just an Idea: As volume make things cheaper. Perhaps maybe people within the community would like to also order a next revision 3 full PCB print run version to work on Mark-2 support.

If the price is right, I would…

Hey j1nx,

Our first goal is to get them out to all of our internal team. I’m also yet to get my hands on an SJ201!

and the next milestone is getting the Dev Kits out to the community. First preference for this has to go to existing dev kit backers, but it could be a good idea to see if others want to order these also.

If others would be interested in this please shout out.


I have never heard of a “Mark-II dev kit” before - am I qualified as a regular Mark-II backer?

Yeah it was one of the tiers you could select, it doesn’t include the case so was intended for the DIY makers / hackers. But if you backed a dev-kit or above then I’m sure we can work something out :slight_smile:

@gez-mycroft Perfectly understandable. I was just late for the game, but considering the kickstarter date in comparison of the current date, most of the current community members are :stuck_out_tongue_winking_eye:

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