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.
— Tom Hall (@Tom_AK2B) August 4, 2014
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.
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.
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.