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The XR-2206 from Exar© is a great IC because, with a few components, it makes it possible to build a circuit that generates analogically various waveforms with a frequency from 0.01Hz to 100MHz. This capability allows you to build quite easily a function generator useful to test audio devices and all the circuits that require a low frequency input.
By exploiting the characteristics of the IC, I provided the PCB with two outputs: one suitable for testing analogue circuits, one for testing digital ones.
A full-optional function generator with XR-2206
In order to comply with the characteristics of a traditional analogue function generator, I made a couple of considerations around the XR-2206:
- since the square wave output’s level is not adjustable by the IC, I thought it would been better to adapt it to the TTL level;
- I designed the circuit to accept a dual power supply in order to calibrate the ground in the “middle” of the sine/triangle wave output signal (DC=0V).
From this, I chose to organize the two outputs as shown in figure 2.
The schematic I drew in figure 3, is basically a combination of the applications suggested on the data sheet and adapted to my requirements explained just before.
Despite the XR-2206 accepting a wide supply range, the 7404 requires 5V. Hence, the power supply must be ±5V.
The function generator at work
A wave generator is not only suitable for testing circuits and devices, it can be used as a musical instrument. In the 70s’ indeed the analog oscillators were very common and they were for instance the basis of the most famous synthesizer: the minimoog.
Inspired by this, I connected the function generator to my audio system in order to hear how the waves sound. Then, I made the video below.
Building and testing the PCB
A STRANGE PLACEMENT
I know, the PCB on figure 4 could seem a bit strange or at least unusual: mixed terminals and trimmers’ model and potentiometers out of the board. The reason? Simple, I wanted to use a cut of double side board left over and the components I already had (as usual it happens to me I have to say…).
You have probably also noticed that some components are placed on the top side board; some others on the bottom one. I think it is the best arrangement if you want to install the PCB on a panel’s box.
As usual the first thing to do before soldering the components in the case of a double side board, is to put in communication tracks by the vias. A good solution consists in soldering a thin unipolar wire to the two sides of the vias. In any case, be sure to do a good job and test the connections with a multimeter, otherwise fixing an issued via located under a component could be very annoying.
After that you can pass on to soldering all the components on the proper side of the board.
ABOUT THE POTENTIOMETERS
Below, I’m going to explain the trick I adopted for soldering the potentiometers in a horizontal position:
- fetch a pin header strip and cut a piece of 5 pins;
- take out the second and the fourth pin and solder one end of the header to the board;
- then, solder the other end to the potentiometers’ holes if you have a model similar to the ones I used (have a look on figure 1); otherwise bend to 90° the potentiometers’ pins and solder them to the header.
Download the project
Pressing the button below you can download a compressed file with all the necessary material to build this project:
- the XR-2206 and 7404 data sheet;
- the pictures of the final project, the schematic, the PCB mask and the PCB layout as shown in this post;
- the schematic and the board files in Eagle format.
If you need some help please do not hesitate to contact me or leave your comments below. Enjoy it!
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