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 14~35 volts. 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 ...
Upon turfing out the parts we are presented with:
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:
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:
followed by the switches, terminal blocks, IC sockets and the ICs:
and finally the potentiometers:
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:
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?
In the next few weeks I plan to rebuild this in conjunction with the matching frequency counter kit, and mount them into a small enclosure which should make a nice piece of equipment to have on the bench or perhaps give away. So stay tuned...
You can purchase the kit directly from Little Bird Electronics. As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts. Or join our Google Group.
High resolution images are available on flickr.
[Note - The kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]
Otherwise, have fun, be good to each other – and make something!