Arduinoos

Part 1, 2, 3, 4, 5, 6, 7, 8, 9

Here we go for some measurements obtained from the previously described Direct Digital Synthesizer.
Measurements have been performed using a Rigol DS1052E Digital Storage Oscilloscope (DSO), originally 2 channels/50 Mhz, which has been uprated to 100 Mhz (See how here).

The Channel 1 (yellow plot) probe is attached to the end point of the R2R ladder, using a single anti aliasing capacitor. The value of this capacitor may change depending upon the targeted frequency, or even removed for squared signals. The Channel 2 (blue plot) probe is attached to the cycle clock signal (which is by design half the signal frequency). The low frequency signal plots include the clock signal and its computed frequency (based on pulses duration).

Frequency: 100 Hz, Sine wave

Frequency: 100 Hz, Square wave

Frequency: 100 Hz, Triangle wave

Frequency: 100 Hz, Saw teeth

and

Frequency: 100 Hz, Noise

Custom: 100 Hz, sin(a x)*sin(b x)

Sine: 1 kHz

Sine: 5 kHz

Sine: 16 kHz

Note: Accurate frequency shall be achieved by removing all unecessary instruction; so that the synch clock signals are discarded. I used the counter option here, which has a different and more accurate way of computing frequencies.

Look at that! Arduino complemented with a couple of passive components can achieve remarkable performance, probably good enough for testing audio equipment.

Part 4