I had the idea of using the Cheap Yellow Display CYD for a graphical user interface for the Cosine Wave Generator that I programmed some time ago.
Because DAC_CHANNEL_1 is used for the photoresistor in the CYD, the settings only affect the second channel. When starting, the generator displays the reference frequency f0. If this deviates from the actual measured frequency, this can be corrected manually. I measured 132.5 Hz on my CYD and therefore set f0 accordingly.The theoretical frequency range is 15 .. 8'000'000 Hz, but only the audio range 15 .. 15'000 Hz is reasonably usable.
In the CYD, the output of DAC_CHANNEL_2 is connected to the input of the built-in amplifier. Because the wiring of this OpAmp is not optimal, I have modified it as described here with the following resistor values: R7 = R8 = 18K, R9 = 33K
Here are the settings and output signals for minimum and maximum audio frequencies measured at a speaker pin and to ground.
| Settings 16 Hz | Oscilloscope |
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| Settings 15 kHz | Oscilloscope |
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