Tag Archives: exar

Kit review – Sparkfun Function Generator

Hello readers

[10/09/2011 Update – It would seem that this kit has been discontinued – most likely due to the unavailability of the XR2206 function generator IC – which is a damn shame as it was a great kit. If you are ‘feeling lucky’ eBay seems to have a flood of them. Purchase at your own risk!]

Time for another kit review (anything to take the heat off from the kid-e-log!). Today we will examine the Sparkfun Function Generator kit. This is based from an original design by Nuxie and has now been given a nice thick red PCB and layout redesign. Although quite a bare-bones kit, it can provide us with the following functions:

  • sine waves
  • triangle waves
  • a 5V square wave with adjustable frequency

There are two frequency ranges to choose from, either 15~4544Hz or 4.1~659.87kHz. Your experience may vary, as these values will vary depending on the individual tolerance of your components.  The coarse and fine adjustment potentiometers do a reasonable job of adjustment, however if you were really specific perhaps a multi-turn pot could be used for the fine adjustment. With the use of a frequency counter one could calibrate this quite well.

The maximum amplitude of the sine and triangle waves is 12V peak to peak, and doing so requires a DC power supply of between 14~22 volts (it could be higher, up to 30 volts – however the included capacitors are only rated for 25V). However if you just need the 5V square-wave, or a lower amplitude, a lesser supply voltage such as 9 volts can be substituted. After running the generator from a 20V supply, the 7812 regulator started to become quite warm – a heatsink would be required for extended use. The main brains of the generator are held by the Exar XR2206 monolithic function generator IC – please see the detailed data sheet for more information.

Now what do you get? Not much, just the bare minimum once more. Everything you need and nothing you don’t …

bagpartsss

Upon turfing out the parts we are presented with:

thepartsss

Not a bad bill of materials – nice to see a DC socket for use with a plug-pack. Considering the XR2206 is somewhat expensive and rare here in the relative antipodes, an IC socket would be nice – however I have learned to just shut up and keep my own range in stock now instead of complaining. Having 5% tolerance resistors took me as a surprise at first, but considering that the kit is not really laboratory-precision equipment the tolerance should be fine. One could always measure the output and make a panel up later on.

Once again, I am impressed with the PCB from Sparkfun. Thick, heavy, a good solder mask and descriptive silk-screen:

pcbss

Which is necessary as there aren’t any instructions with the kit nor much on the Sparkfun website. The original Nuxie site does have a bit of a walk through if you like to read about things before making them. Finally, some resistors and capacitors included are so small, a decent multimeter will be necessary to read them (or at least a good magnifying glass!).

Construction was very simple, starting with the low-profile components such as resistors and capacitors:

resiscapsss

followed by the switches, terminal blocks, IC sockets and the ICs:

icsss

and finally the potentiometers:

potsss

The easiest way to solder in the pots while keeping them in line was to turn the board upside down, resting on the pots. They balance nicely and allow a quick and easy soldering job. At this point the function generator is now ready to go – after the addition of some spacers to elevate it from the bench when in use:

finishedss

Now for the obligatory demonstration video. Once again, the CRO is not in the best condition, but I hope you get the idea…


Although a very simple, barebones-style of kit (in a similar method to the JYETech Capacitance meter) this function generator will quickly knock out some functions in a hurry and at a decent price. A good kit for those who are learning to solder, perhaps a great next step from a TV-B-Gone or Simon kit. And for the more advanced among us, this kit is licensed under Creative Commons attribution+share-alike, and the full Eagle design files are available for download – so perhaps make your own? High resolution images are available on flickr.

[Note – The kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

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