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Yahama BC-1 (BC-2, BC-3) connecting experience and question


skunks
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Hello guys!
I'd like to share my experience of connecting Yamaha BC-1 breath controller to Core LPC (using MIDIbox NG application).

First of all, I'm sorry but I didn't manage to obtain any AINSER module, so all test are done using onboard ADC.

 

All 3 BC's are powered with 9V and output values in the upper half, but in a "mirrored" manner: higher voltage in rest and lower voltage when blown into. BTW, one can also suck the air in, then output value goes even higher, but doesn't reach 9v.

BC-1 and BC-2 have a diode on their outputs (don't know about BC-3), so a pull-up resistor must be used (without it the output is "hanging": I get a random flow of CC values).

58d5360f83114_BC-1scheme.thumb.png.9d4b7

 

There is a (not so good) option to power BC's with 5V, I saw this approach several times in the Web (e.g. for connecting to expression pedal input of a synth or to some commercial controller similar to sensorizer, e.g. Doepfer WE):

5v.png.565293fab39eb498cc85ec1029c5b6e1.

 

I've found the following page on one forum (without a link to the source, but we may guess it's somehow related to some controller named MIDIBOARD):

9V.thumb.png.50b6434e9bca4abf0052d6f170f

So after several experiments with different schemes and voltages, I settled on the above scheme.

Doepfer WE manual recommends pull-up resistor from 1k to 4k7 (however, for 5V supply).

Because above schematics outputs values more then 3.3V, I had to use a simple pot-based voltage divider instead of a pull-up resistor. I calibrated it and everything works fine... almost.

 

Here was a good part.

There is one annoying thing I still trying to get rid of:

At first I used 47k pot as a divider. I've got a lot of 127 values in the flow. Even if I do nothing, they are flowing, like: 60, 127, 60, 127, 60, 127, etc. (60 is my value at rest if not adjusting pinrange etc, but simply setting output 0..127 mapped to 0-3.3V). I tried to increase the current by replacing my pot with 1.4k. It helped - now 127 values appeared ~ twice a minute. And finally I replaced my pot with 640 Ohm. Now I get 127 once a minute.

So the problem is I cannot eliminate sporadic 127 values completely. And 640 Ohm divider I think is a waste of battery ;)

 

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I forgot to mention:

3.3V is insufficient to feed BC's opamp.

Feeding with 5V (taken from the core module) is a bad option because:

1. Output range is only 25% of 3.3V (CC values are 57 to 76 if mapped to 0..127), so much less resolution compared to floating ground 9V approach, that truncates unused lower half of the output.

2. It doesn't produce any changes if I suck the air in.

But, I don't know why, I had no sporadic 127 values when powering with 5V from the core (I used 1.4k pot as a divider). May be the testing time span was to small so they didn't occur, I'm not sure.

 

Cable of my BC-1 is very thin and obviously unshielded.

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