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A simple Si5351A breakout board

February 19th, 2015

I have been toying with the idea of making a Si5351A breakout board ever since I saw the chip details on Silicon labs web site. It seems  SI5351A is an ideal choice for Variable Frequency Oscillator (VFO) for a homebrewed radio.  The SI5351 is an i2c programmable any frequency clock generator. The chip can  generates up to 8 non-integer-related  frequencies from 8 kHz to 160 MHz depending on the model. There are 3 different variations of the chip currently available.  For the home brewer SI 5351A looks promising as it is available in a 10 pin MSOP package.

For the ham radio home brewer, such a chip which can be programmed over many ham bands offer  numerous possibilities.   The most obvious choice would be  as a VFO. Currently, the analog devices DDS chips are ruling the market. Compared to them the Silicon Labs chips are cheaper and less cumbersome to handle. I am yet to see the noise performance of these two chips compared.

In fact, there are a couple of commercial Si5351A breakout boards   targeted at the  home brewer. They cost around 10$. But the chip itself cost only 1.33$  on the Silicon Labs website and you need only a few  additional components to complete the board. The total cost need not be more than 3 $.  Along with a cheap Arduino clone, Si5351A gives you lot of flexibility. An added advantages is that the SI5351A  has three independent programmable clock generators. You can combine  the  VFO and   BFO  into a single chip.

My idea was to build a single side PCB so that any one can build one via toner transfer. Last week,  I had a long  chat  with my friend and colleague Amal Dev  about designing  a simple board.  The board routing was done by Amal Dev on eagle,  We have  designed an experimental single sided board and it may not be conforming to RF design principles always.

For the interested home brewer a  toner transferable image is  here.    You can  buy the  SI5351 from RS components  or from Mouser.  The board is to be powered from a 5v source.  The SI5351A needs 3.3v for its operation. The LM1117 is used for generating this.  Note that the LM1117  is SMD and is soldered on the copper side.  The two MOSFETs ( BS170)   are used to convert the I2C levels from 5v to 3.3v.  Check the pin outs before you solder.  The board can be directly powered from an arduino.

For programming the board you can try the example code from Hansummers.  Alternately you can try the excellent si5351 arduino library.  Tom Hall AK2B has some  sample sketches using this library. Please note that I2C address of the chip may be different from those found in the above code. Please use an I2C scanner  to find out your chips address and then modify your code accordingly.

si5351 breakout board

Schematic of si5351 breakout board. Q1 and Q2 are bs170. The regulator is a smd lm1117




Si 5351 board.


Component Placement on the Si5351 break out board.

The pin out of the SI5351A is shown below.


A special thanks to Amogh Desai who tested the first version  and reported couple of errors.  Further comments and error reports are welcome.

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  1. February 19th, 2015 at 23:11 | #1

    Well done sir, this was the most wanted item in the homebrew shack…. congrats and wish to have two piece.

  2. Parth Sane
    February 20th, 2015 at 16:50 | #2

    How does this match up or compare with the performance of AD9850? Curious to know!!

  3. vu2swx
    February 20th, 2015 at 18:28 | #3

    I think it is much better than analog ones. I have not done any serious testing.

  4. Satish Chandorkar
    February 20th, 2015 at 20:51 | #4

    Very well done, I was following Charudatta Uplap for the same. When the PCB’s will be available? Tentative value of the PCB?

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