Electronics > Projects, Designs, and Technical Stuff
Breath Controller for synths w/ BC input: need design help
cpwhite:
I think there is some confusion here.
Disassembling my Yamaha BC2 I find what is almost certainly a Hall Effect senior for IC3, not a pressure sensor. There is a rubber bladder for lack of a better term which the breath mouthpiece is connected to. On the PCB side of this bladder is a small magnet. This sits directly over IC3 when the BC is assembled. When blowing into the mouthpiece, the bladder inflates and the magnet moves closer to IC3, increasing the output voltage. Hall effect sensors, for those who don't know, vary their output according to a magnetic field. There can be a linear device like this one, or they can be magnetic switches. https://en.wikipedia.org/wiki/Hall_effect_sensors
Pressure sensors generally don't like moisture and because in a breath controller, we're breathing humid air into the system, a pressure sensor would likely deteriorate over time. A moisture filter could possibly solve this problem, or a pressure sensor that has a built in moisture barrier. I think the fact that Yamaha didn't used a pressure sensor, but a rubber membrane with a magnet and hall effect sensor, reinforces the difficult in using a pressure sensor. So the iT43094 isn't a pressure sensor, but is a hall effect sensor. I couldn't find any datasheets on the web for this part number, and the part itself on my BC2 is marked 05. It's a small four pin surface mount IC.
I've posted photos on my web site that show the plastic square which holds the rubber bladder and clearly shows the magnet in the center. I also took a picture of the component side of the PCB which shows the hall effect sensor in the center of the board and the case. http://www.chuckwhite.com/yamaha-bc2.html
cpwhite:
LM358 will be fine. It's a good lower power opamp.
stubbsonic:
I just got word from Kurzweil support about the current maximums. It said the maximum safe current was 23.8 mA, and that the suggested maximum current is 20 mA. I'll update my initial post with that info.
Also, just a note that I received a circuit design from Chuck White (THANKS CHUCK!). I just now assembled the parts and can begin wiring up and testing the design! :D
artico78:
Very interesting, i ordered some breath sensor to made a test with my kurzweil pc3k7 and find your post searching material about BC3a, for my test i ordered MPX2010DP e MPXM2010GS they will arrive from Malesia in January, i will try to made all in smd technology. I follow your post with interest. CPwhite its interesting the all effect sensor, ive some at home that i bought for my CNC, i found a 4 pin hall sensor http://www.digikey.com/en/articles/techzone/2011/may/micropower-hall-effect-sensor-ics-for-mobile-apps
stubbsonic:
Thanks for chiming in, artico78. As of Nov 2015, this is an actively evolving topic.
First of all, congrats to happyrat1 who guessed the max current exactly at 20 mA. That was the one missing piece of info, so we are all good to go.
FIRST BUILD & TEST:
I took advantage of the day off and breadboarded the circuit I got from Chuck White. My first test didn't work (read a steady voltage on the meter). I directly tested the sensor which is working as expected. Now I need to determine if I wired things correctly, AND whether I tested it correctly. I suppose there are relatively few variables, but still somewhere I didn't get it right. I'll communicate directly with Chuck to compare my wiring diagram with his circuit-- perhaps he can help me see where I got it wrong.
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