DIY Function Generator 20Hz - 100KHz with XR2206 IC
In this short review we would like to introduce you schematic for our DIY Function Generator XR2206 Kit.
As you can see it contains only several components. XR2206 is very interesting chip manufactured by EXAR and it was designed to produce sine, triangle and square wave. The output frequency has 4 ranges and you can toggle the timing capacitor C4 - C7 with a jumper or rotary selector. R6 is the coarse control and R9 is the fine control of the frequency. R3 is the amplitude control. R10 is determines the minimum amplitude level. You can do some experiments with it value.
Actually the XR2206 IC can generate up to 1MHz, but to keep good control linearity we reduce the total frequency ranges of the kit to 20Hz - 100KHz. However you are free to experiment with R5, R6 values to increase the output frequency.
R1, R2 ratio control the frequency offset and we use in the kit two 1% tolerance resistor. But you can use external rotary potentiometer 10K instead R1 and R2 to control the offset.
R7, R8 is the sine wave calibration trimmers. If you have scope you can calibrate the purity of the sine wave to 0.5% TDH. In case you can't reach a oscilloscope, then trim R8 to 200 Ohm before power on and ignore R7 installation. Without calibration the XR2206 IC can produce sine waves with 2.5% THD.
Calibration should be made as follows:
1. Set the S/T jumper to close for the sine wave output.
2. Set frequency jumper to C5 100nF.
3. Connect 12V power supply and oscilloscope probe. Power up the device.
4. Set the amplitude to the maximum with R3.
5. Set the frequency to 1KHz with R6 and R9.
6. Use a screwdriver to trim R7 to the midpoint and adjust R8 for minimum distortion.
7. With R8 set as above, adjust R7 further reduce distortion.
R4 is a pull-up resistor to square wave open collector out. The square wave output frequency is also controlled by R6, R9. But R3 has no effect on the amplitude of the square wave.
The XR2206 has 20ppm/C temperature stability. However we supply high quality timing capacitors C4 - C7 for frequency ranges to reduce temperature drifts.
The kit is very simple to solder if you follow our PDF manual. For short demonstration video and full technical specification of the kit please follow the link: