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Mystery gift

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Mystery gift

PostPosted: Fri Dec 07, 2018 12:01 am
by BJG145
I just picked up an old breath controller, a Yamaha BC2, and there was an extra gadget in the box:

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It looks DIY, with a 3.5mm stereo socket (presumably for the BC2), and a lead with a mono 1/4" jack. They're spliced together with a resistor across the join, one lead from a 9V battery connected to one side of the join, and the other lead from the battery apparently going to the third pin of the input socket.

Any thoughts on what this arrangement might be used for...?

I'm interested in putting together an Arduino-based MIDI converter for it, like the MIDI Solutions Breath Controller or Anatek Wind Machine. There are some notes on the BC2 here, though I don't really understand the statement:

...the Tip (red wire) of the stereo plug is ground, the Sleeve (black wire) is +Volts and the Ring (white wire) is the output voltage.
.
What is "+Volts" here...? Is this what the 9V battery is supplying...?

Re: Mystery gift

PostPosted: Fri Dec 07, 2018 12:53 am
by Hugh Robjohns
The breath controller is an active device and needs power, hence the 9V battery, and it appears to need volts on one terminal of the 3.5mm plug, reference ground on another, and the output control signal on the third.

I'd be surprised if the sleeve really is +V and the tip ground... Worth checking with a meter. It's possible the supply volts needs to be negative rather than positive (relative to ground).

I'm guessing it was designed to be powered from some other bit of Yamaha gear, but the previous owner of this unit used it with something else that didn't provide power.

H

Re: Mystery gift

PostPosted: Fri Dec 07, 2018 1:03 am
by Martin Walker
Yep, the Yamaha BC2 contains a hall effect sensor that requires a supply voltage to operate.

Here's a circuit diagram that explains what's inside:

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So, yes, the Tip (white wire) of the stereo plug is ground, the Sleeve (black wire) needs to be connected to that PP3 battery for +9V, and the Ring (red wire) is where you access the BC2 output voltage.


Martin

Re: Mystery gift

PostPosted: Fri Dec 07, 2018 1:14 am
by Martin Walker
I have Yamaha's earlier BC1 breath controller, and this circuit diagram makes more sense, since the sleeve is earth, and the tip is designated as -9V, with the sleeve once again as output signal:

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Martin

Re: Mystery gift

PostPosted: Fri Dec 07, 2018 1:40 am
by Hugh Robjohns
Well done Martin. All becomes clear!

H

Re: Mystery gift

PostPosted: Fri Dec 07, 2018 10:02 am
by Folderol
Those are seriously brain-dead wiring colours :o
I would suggest the reason for the earthing change is that the sensor itself has a connection that is also an interference shield, and they used a slightly different sensor in the newer model.

It's quite an interesting circuit actually.

IC2a creates a 'virtual' rail at half the supply voltage so all the other ones think they are getting + & - supplies. IC2b is unused but wired so it can't 'flop about' and create interference.
IC1a takes the differential output from the sensor, amplifies it and makes it single ended.
IC1b provides more gain (depending on those unstated resistor values) and DC balancing and control isolation.

As for the resistor, it's needed as it provides bias so that the output diode is always conducting. However it looks like a carbon one so I would be inclined to change it for a modern metal film one. You can see that the original receiving device has something like that built-in.

If you are running into and Arduino instead, I would suggest you find out what the actual voltage range of the breath controller is, then make an appropriate potential divider so you don't overdrive the Arduino's input. In any case, I always feed the analog inputs via a 10k resistor and shunt 47n cap. That provides filtering as well as current limiting in case of overloads.

P.S.
Of course, if running into an Arduino you can do away with that box and put its functionality into the Arduino box :smirk:

Re: Mystery gift

PostPosted: Fri Dec 07, 2018 10:13 am
by BJG145
Great, thanks for that... :thumbup:

Re: Mystery gift

PostPosted: Sat Dec 08, 2018 3:04 pm
by Melody7
BJG145 wrote:I'm interested in putting together an Arduino-based MIDI converter for it.

If you want to use breath control with a computer, there are ready made solutions with USB-MIDI interface that work great:

http://www.tecontrol.se/products/usb-midi-breath-controller
http://www.tecontrol.se/products/usb-midi-breath-bite-controller-2

Re: Mystery gift

PostPosted: Sat Dec 08, 2018 3:34 pm
by Folderol
Ummm, this is the DIY forum :lol: :shh: :wave:

Re: Mystery gift

PostPosted: Sat Dec 08, 2018 5:55 pm
by BJG145
I wish I could read circuit diagrams like you Folderol. :tongue:

It's useful to have some electronics wizards around when people are trying to blow things up.

(I checked with the seller, and he said that he made it, but he couldn't remember why.)

Re: Mystery gift

PostPosted: Sun Dec 09, 2018 1:03 pm
by Melody7
Folderol wrote:Ummm, this is the DIY forum :lol: :shh: :wave:

I know but it has happened to me that I DSM (Did Something Myself) because I did't know it already existed, and If I had known before I wouldn't even have thought of doing it myself.