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the wondrous tales of a software guy in hardwareland

And Now We’re Up To Something

Yes sir, my first “track” is available on SoundCloud. Don’t expect anything musical, however :-)

I managed to hook the monotron to the Arduino and made the DAC working. Can’t be really called a sequencer yet, I just concocted some quick code to test controlling gate/pitch and cutoff from Arduino. Here is how it sounds, in all its glorious crappiness:

The sequence is always the same, only the cutoff varies from step to step (sometimes it’s so low that you can’t even hear it, that’s why it sound like the monotron is “missing” a step). I’m fiddling with the monotron knobs while the sequence is running, just to test that everything is properly working.

As I expected, tuning and getting everything in range is the most difficult part. At first, I tried connecting the output of the DAC directly to the monotron, but it wasn’t happy at all. Fortunately it didn’t break, just acted somewhat strange. I love how this little thing is sturdy :-)

In the end, I found out that 33k resistors for both pitch and cutoff work best. I tried also with 10k, and with an additional trimmer as the Din Sync page suggests, but it didn’t work very good. In particular the cutoff seemed to be way off base.

While testing the DAC, I also discovered that I wasn’t completely right about SPI. The error was to reuse the MISO pin (number 12, that’s the SPI “read” channel) as one of the SPI slave select pins. This simply doesn’t work, because even if you don’t need MISO, the SPI library sets it as input, and it can’t used as an output.

This means basically that I can’t use 2 x MCP-4921. Actually, I can, but I have to use another pin and leave the 12 alone, which means I’m short of one pin. Fortunately, I also bought an MCP-4922, which is a double DAC chip, and I can do everything with only one SPI slave select pin. Yuhuu! :-)

Well, the hardest part is now done. From now on, it’s just a matter of assembling the monotrino and write the code. Piece of cake :-)

cheers,
Aldo

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