The XR-2206 provides a square wave at an open-collector output, as well as a sine wave. It can produce a triangle wave, but this is really just a step towards the sine wave, and is seldom required. The frequency is set by a capacitor, in the range 0.001 - 100 μF, and a timing resistor of no less than 1k, but preferably between 4k and 200k. There are actually two timing resistors, and which one is used is selected by the level on pin 9. When pin 9 is open or above 2 V, the resistor called R1 is used. When pin 9 is below 0.8 V, R2 is used. This gives easy frequency-shift keying (FSK) by a logic input to pin 9.
A circuit for testing the XR-2206 is shown at the right. The 25k pot adjusts the symmetry, and the 500Ω pot adjusts the waveform (so the data sheet says). I found the 25k control to be best about in the center, and the pot adjusted to 203Ω. The 50k pot adjustment is also important. This circuit sets the average value of the output waveform (here to 6.0 V) and its amplitude. If the amplitude is not set correctly, the waveform will have flat tops or bottoms, or both. I found 38.6k the best setting. It is nice to have the pots to see what they do, but if you don't have them, use fixed resistors instead (2 - 12k, 200Ω and 39k) and you should be all right. The proper adjustment of these controls is necessary for a good-looking sine wave. The XR-2206 makes a quite passable sine wave.
The frequency is about 1/RC. I found 10k and 0.01 μF to give 9759 Hz, 100k and the same capacitor 1018 Hz. 1k and 0.001 μF gave 664 kHz. Pins 7 and 8 are held at 3 V, and more than 3 mA should not be drawn from them, so 1k is the minimum timing resistor. The chip is advertised to work down to 0.01 Hz! I used a 10 μF tantalum (+ to pin 5) and R = 1 M, and found a period of 8.2 s, timing 10 oscillations with a stopwatch. Reducing R to 2k gave an ideal 20 ms period, or 50 Hz. The output was centered on 6.0 V, and its peak-to-peak amplitude was 6.0 V as well.
The XR-2206 has an AM input at pin 1. I used modulation at 1.0 kHz, 4.0 V peak to peak, and DC bias 4.0 V, for 100% modulation. The DC bias at this input is necessary, and the signal amplitude must be properly adjusted. The 664 kHz signal could be picked up on an AM radio at the expected frequency, and the modulation heard. I simply put the end of the whip antenna of the small pocket radio near the output of the XR-2206, and got plenty of signal. One could make a small AM radio transmitter with this chip for use over short distances.
The output frequency can be modulated by an external voltage using the circuit shown at the right. R is the normal timing resisor, while RC handles the modulating current. The formula for the frequency is shown in the figure. If the applied voltage V is 3.00 V, the frequency is as determined by R. An increase in V lowers the frequency, and an increase raises it. Using R = 2.0k and RC = 1k, I could vary the output frequency from about 10 kHz down to 2 kHz by swinging V from about 1 V to 4 V. In any case, do not exceed 3 mA from pin 7 or 8. I was fairly close to the limit here, but RC = 2.0k for VC from 0 to 6 V would be OK. Use a buffered potentiometer to test the dependence of frequency on VC. Supply VC from a function generator, setting the DC bias at 3.0 V, and varying the amplitude over a small range, at a frequency of, say, 2 Hz, and watch the result on the scope. The waveform looks like a spring extending and contracting! Modulating the frequency with an external signal has quite a few applications. One is displaying frequency response on the scope--you might try this with a parallel resonant circuit. Feed Y and the XR-2206 with a triangle wave, and X by the rectified voltage across the tuned circuit. FM would also be good for testing a phase-locked loop.
The XR-2206 offers many possibilities for sine wave generation and modulation over a wide range of frequency. The output can be buffered to adjust its DC component and signal amplitude. Frequency can be varied by a range switch and a potentiometer, so that one could make a fairly useful function generator based on this chip, at low cost. With the XR-2211 FSK detector, it is easy to make an FSK data link.
1Hz - 2MHz XR2206 Function Generator Kit
Function Generator is an essential laboratory equipment for every electronic. It allows a variety of measurements and experiments. The module described here is based on high quality XR2206 IC. 1Hz - 2MHz XR2206 Function Generator is capable of producing high quality sine, square and triangle waveforms of high-stability and accuracy. The output waveforms can be both amplitude and frequency modulated.
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