I added a basic breath sensor to the pastry saxophone. It kinda works! The response of the breath sensor is quite slow - I think I need to use something stretchier than a nitrile glove. It doesn't feel sensitive enough to do staccato notes or anything yet.
I didn't get dynamics working with the USB MIDI yet, but on/off breath control works well
The breath sensor works like this guy's video: https://www.youtube.com/watch?v=es92GqYBge0
The black tape all over it is to block out light - I found it was making a big difference to the readings.
I've started printing the mouthpiece and designed the sensor half of the breath sensor. This uses a TCRT5000 IR reflectivity sensor, which shines at a diaphragm clamped between the two halves.
When you blow into the mouthpiece, the diaphragm expands towards the sensor, increasing the amount of IR that's reflected back into it.
Dynamics now work! I'm using the breath velocity value from the cardboard breath sensor to set the MIDI breath controller value, and mapping that to volume in the synth. I'm sure there's a much more complex and nice-sounding config that can be done, but this is cool!
It needs to be a bit more linear, but that just means making some sort of calibration curve for the sensor. That can wait until I've got the 3D printed one working.
I've put the code up on https://gitlab.com/gbrnt/electro-sax
There's currently a latency problem - I need to check whether it's on the Arduino end or on the computer end. The breath sensor has some extra latency - I think that comes from the current prototype but I'm not entirely sure.
The end-to-end latency of the electro-sax is definitely too high right now. It's recommended to get it below 10ms (if you can) and here it is at 160ms.
That's enough that when you're doing something like a run of short notes you do one too many because the sound hasn't caught up yet.
Let's see how much I can improve this just by changing Jack settings. Not sure how Pipewire comes into this.
So far in my attempts to improve the sensitivity of my breath sensor, I've managed to make it worse.
The first cardboard prototype had a range of 0.38V, or 77 counts in an Arduino's 10-bit ADC. Ideally it'd be more than 127 for a completely step-free MIDI reading.
The 3D printed prototype got me 18 with the nitrile glove membrane, or 31 with a white balloon. Not great. Hopefully the sensor I designed it for will arrive tomorrow and I'll be able to try it out.
Hmm, not doing great with the BMP280 pressure sensor. It works really nicely for detecting a change in pressure, but it doesn't seem to be very good at going back to its original zero point.
So in the screenshot you can see the lows are at different points each time I stop blowing. I assume it's doing something clever, but whatever it is it makes it less useful to me.
@gbrnt Seems like it would be usably accurate only if the air pressure changes happen at strictly regular instances.
@AskChip There's an intentional leak, the chamber is essentially a tube with a flow restriction at the outlet. So when I stop blowing it should always be the same pressure inside (ignoring atmospheric pressure variations)
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