1Hz-2MHz Function Generator Kit

After building the “Accurate LC Meter Kit” from Electronics-DIY.com, I turned to their “1Hz – 2MHz XR2206 Function Generator Kit”. All parts necessary to complete the kit were included, though not exactly as pictured on their webpage — two of the WIMA capacitors had been replaced with substitutes and there was no IC socket. All components were through-hole; soldering the kit together went quickly and easily.

If you build one of these kits you’ll need to provide your own power source as well as your own pin-connectors (if you choose to use the pins provided). As with the LC Meter, I used a size M coaxial DC power jack to accept a plug from one of the wall-wart power supplies I have around here. I didn’t bother to install a power switch in either unit since I won’t be using them very often; I won’t leave them plugged in between uses.

The fellow at the local Radio Shack gave me some pin-connectors for free, clipping them off of some battery packs that were in a box for recycling, though he only had two-pin connectors. Since one of the pin-sets has three pins, I just soldered a piece of hookup-wire to the third pin. If I had to do it all over again, I wouldn’t bother with these pins — I’d just solder hookup wire right to the PCB. By the way, if you ever try soldering to a pin make sure you clip a heat-sink to the pin before heating it up. The plastic base of those pins melts pretty quickly!

I chose a plastic project box from Radio Shack to house this function generator. Using a Dremel tool with an engraving cutter (at the lowest speed — 5,000 RPM), I put three notches in one side of the box for the potentiometers, a notch on one end for the two switches, and ground down all four stanchions on the floor of the box since otherwise the potentiometers would have extended too high to allow the lid to fit. That Dremel tool sure is handy! A few knobs from Radio Shack finished off the project.

The two outboard switches allow you to select between three waveforms — sine, triangle, and square. I don’t have an oscilloscope so I can’t tell you how the waveforms look, but I can at least tell you that the sine wave sounded pure when I hooked my headphones up to the output with a matching pad. I am pleased to report that the signal generated by this function generator is very stable. Four DIP switches on the PCB allow you to select between four frequency-ranges, and two potentiometers allow you to tune within the selected range. One of these two potentiometers provides coarse tuning, and the other provides fine tuning. The third potentiometer controls the amplitude of the signal generated (note: amplitude decreases as you turn this potentiometer clockwise).

If you build this kit you’ll want to hook it up to a frequency counter. Two pads on the PCB are provided for this purpose. I have a piece of coax hanging out of the back of the box for connection to my own frequency counter — not that you have to use coax, but it was handy for terminating with a BNC connector. (If I were really classy I would have put this coax through its own hole in the project box, but hey, this is a piece of test equipment — I just ran it through the big hole I made for the RCA connector.) When I hooked up my frequency counter I noticed that the published ranges for each DIP switch were just rough approximations, but I was pleased to see that this frequency generator covered the entire published range and more — up to about 2.4 MHz, if I recall correctly.

Here is a slideshow of photographs I took of the completed function generator:

This slideshow requires JavaScript.

The source impedance of the generator is 600 ohms and the output is intended to be terminated in a 600-ohm load. In my next post, I hope to discuss the construction of a minimum-loss matching pad to hook it up to a piece of equipment that has a different input impedance.

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4 Comments

Filed under Kit Building, Test Equipment

4 responses to “1Hz-2MHz Function Generator Kit

  1. Douglas

    Waiting for the follow on article?

    • Todd Mitchell

      Hopefully soon. I still have some work to do before publication. Lord willing I’ll have it done in two weeks or less.

      By the way, this signal generator really saved the day last Saturday. After considerable hair-pulling my friend and I discovered that the LC meter kit I built was bad. It seemed to work okay as long as the capacitor or inductor was small enough, but close to 1 uF or 80 mH it gave only one reading: 838.8 uF or 83.88 mH, respectively. I shelved the defective LC meter and did it the old fashioned way with this signal generator, a frequency counter, and a voltmeter, finding the resonant frequency of the unknown inductor with a known capacitor. Precision was pretty good, too — with a good FLUKE voltmeter you can narrow the resonant frequency down to one hertz.

  2. Larry Leon

    I’m making a function generator based off of this design. What cao values did they supply for the frequency switching? Also, I was wondering if the dip switch can be replaced with an external single pole, 4 position rotary switch, or to get the range up to 2MHz do you need to have more than one capacitor switched on at the same time?

    Thanks,
    Larry

  3. Glen

    I just built this FG. Your pics are awesome. But I am still a little lost because I am no where near being an electrical engineer, but am a hobbyist. In a sense that I like lighting up LED’s in Star Wars figures.

    I am looking for how to actually use the FG you built. I put it together this weekend and ended up with two switches to idk where. I need to get to a square wave around 147Hz. No clue why, but that’s what I need for my next project. I was hoping this came with a manual.

    I have the RCA plug for output. Do I just cut that and reveal the two wires inside? How do I and what do I use for my power source? I was thinking 8 AA batteries but idk even know where they would go for input.

    Any help would be greatly appreciated.

    Glen

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