Its been some time I have been wanting to use a SI5351 chip to build a VFO. As the cheapest version of this chip (at just $1.30) can be configured to generate up to 3 programmable clocks, it can be put to use in a HAM rig very well. One clock as a VFO and other as a BFO. Simple code on Arduino can generate a LSB and USB signal with no hassle of pulling crystals down or up with inductors makes it so much easy and fun. The 3rd output can be put to use as a CW tone generator.
There are many breakout boards for this chip available, but all in the DX land (QRP Labs, Eatherkit, etc). With multiple projects at hand I was hesitant to order one. I had also been discussing about it online with VU2SWX, Prof. Sunil Thomas who was keen to design a breakout board for the SI5351 himself and subsequently I got this update a couple of days ago at VU2SWX’s Blog:
To build this one I had to additionally buy a SMD soldering Iron (MAX 550) and liquid soldering flux.
Caution: There are errors in this PCB, please wait for an update from VU2SWX.
When I started to build this PCB I figured out there were 2 big errors in the layout. Both the SI5351 chip and LM1117 regulator IC layout on the PCB was reversed. I didn’t want to waste more time so mounted the ICs in reverse and finished the PCB mounting all other components.I burned the SI5351 VFO sketch by AK2B, Tom Hall here to a Arduino Nano and built the VFO as per this design:Here’s my VFO on a breadboard: Here is a copy of the sketch I used for testing: VFO Sketch for Si5351 with IF
The sketch was working perfect but no output from the breakout board. I rechecked the board for connection issues or soldering errors, everything seemed correct. So I set out to check the communication between Arduino and the SI5351 chip. I burned this I2C scanner sketch to the nano and got no result on the serial monitor. This made clear that there was no communication between Arduino and Breakout board.
I cross checked the Level shifter FETs BS170. I realized the board was made for through hole components while I used SMD 1206 package. The Pin for both these packages is different.I re-soldered the SMD BS170 correctly as per pin out and checked the I2C Scanner again. and voila ! This is what I got:
I quickly burned the SI5351 VFO Sketch again and got a clear VFO signal on my dongle !One of these PCB has already been sent to VU2SWX with all the errors and I am waiting to hear from him with a corrected PCB.
In the meanwhile if you have any suggestions or feedback, please feel free to post your comments in the section below.