Etherkit, Homebrewing, Microcontrollers

Si5351A Breakout Board Update

I’ve had a good response to the Si5351A Breakout Board when it was posted on Hackaday last month. There have even been a few folks who went through the trouble of ordering PCBs from OSHPark so that they could build their own copies of the board for experimentation. One of them, Tom AK2B, even constructed a complete receiver using the Si5351A Breakout Board and the RF Toolkit modules from kitsandparts.com. Check out the link to the nice-sounding audio in the embedded tweet below.

When the link to the Breakout Board was posted on Hackaday, I wasn’t even sure that anyone would be interested, so the design was not as robust as it should have been for public use. But thanks to some suggestions from Tomas OK4BX and some of my own ideas, I’ve created a Rev B Breakout Board that has a number of improvements.

Si5351A Breakout Board Rev B
Si5351A Breakout Board Rev B

I increased the size of the board by 10 mm on the short side in order to accommodate some new circuitry. I could have kept the board the same size and put the new components on the back side of the board, but I thought it would be better to keep everything on the front. Thanks to Tomas’ suggestion, I added simple MOSFET I2C level conversion so that the Si5351A can be properly interfaced with a 5 V microcontroller. I also added a 3.3 V LDO regulator and jumper blocks so that the I2C interface voltage and the 3.3 V source can be selected. The traces from the Si5351A to the output transformers were also screened with vias, which improved crosstalk between outputs by about -6 dB. I also increased the pad size for the SMT crystal in order to make it easier to hand solder. In addition, I added a provision for the crystal footprint to double as a footprint for a TCXO. So far, the crystal works fine, but I haven’t ordered the TCXO yet in order to verify that it works as well, but I don’t think there will be any problems as long as the crystal is working.

As I anticipated from a previous post, Adafruit has released their own version of a Si5351A breakout board. It looks like they use the same I2C level conversion scheme as my board, but that is where the similarity ends. The Adafruit board seems to be geared to using it strictly as a clock generator, where the Etherkit board is designed to be used in RF applications by providing output isolation via broadband transformers and screening of the output traces. The Etherkit board also has more flexible options for using the board in 5 V or 3.3 V environments.

You can order the new board from OSHPark here, and find the documentation for it on GitHub.

I need to do a bit more testing to ensure that everything is working as it needs to, but so far the preliminary tests look great. Assuming that everything with the new board checks out, there’s a decent possibility that I will kitting at least one batch of these boards for sale. Stay Tuned.

Design, Ham Culture, Homebrewing

Homebrewing Hangout

As I mentioned in the previous post, I wanted to try the Google+ Hangouts feature to attempt to do a video chat version of the old EchoLink chat that some of us used to have a few years ago on Saturdays. Today we took it for a spin, and I think I really like how it shaped up. We ended up having a total of 12 participants, with about half of the people actively participating, including AK6L, OK4BX, W0EA, LA3PNA, and WG0AT (Steve the Goathiker).

I’ve never used the G+ Hangouts before, so I didn’t really know what to expect, other than a video chat. It turns out that it’s quite a bit more useful than that. For example, you can do screensharing with your PC desktop or a particular window. Tomas OK4BX came prepared with an excellent slideshow presentation of the DDS-driven MEPT that he and his father recently put on the air. W0EA was able to show us the schematic and PCB layout of the amplifier T/R switch that he just sent out for manufacturing. You are also able to switch between multiple cams while in the Hangout, which AK6L used to give us some nice closeups of his projects. I’ve got a USB microscope which is basically a webcam with a high-power lens, so it would work great for showing off close-ups of things as necessary. We also got a neat treat to a live view of WG0AT’s goats Rooster and Peanut, courtesy of his iPhone connection to the Hangout.

The only potential downside that I could see when compared to EchoLink is the free-for-all format versus the way that EchoLink facilitates traditional roundtables. It wasn’t really a problem for our group, but I was at a bit of a loss on how to handle moderation. In the future, I think we’ll start off with a sign-up queue to speak, then end with a free-form chat. There’s also no native list of callsigns to call upon, but using a Hangout plugin (Lower Third), you can add a caption to your video stream with your name and callsign just like a TV chyron.

The overall impression was that the hangout went better than expected. We had some really interesting information presented and the turnout was excellent for a first time. I think this definitely is superior to the EchoLink chat. Now that I have an idea of what’s going on, it should run even smoother next time. If you are not already a member, go to our Google+ Community page (Ham Radio Homebrewing) and join. The next time there is a Hangout, you’ll get an invitation. We’ve scheduled the next one for two weeks from today due to it being close to Christmas next weekend. I’m not sure if this will continue on a weekly or every other week schedule in the future, but we will continue these Hangouts on a regular schedule.