Monday, February 11, 2008
A completely hardware-implemented version of a previous idea. In a way, it is sort of like what they call an 'Arduino Shield' in that it can connect directly to an Arduino board via a set of male headers that attach to the digital i/o pins and ground, and then a separate line for 5V.
The MIDI signal is conditioned and inverted via a 4n25 optoisolator. I also use a 3.57954MHz instead of the value specified in the datasheet (which is 3.12MHz). Mainly because i had a colorburst crystal lying around. Some other values of components for the SP0256 also differ a little bit from other circuits i have seen. I have used a 1n914 instead of a 1n4148 and two 27pF instead of 22pF.
I have also not added the two-pole low pass filter that is normally used to smooth out the PWM digital audio output. I don't really mind the raw sound, and anyway, a lowpass filter can always be added later very easily.