Electronics > Projects, Designs, and Technical Stuff
Breath Controller for synths w/ BC input: need design help
stubbsonic:
Hi, this is my first post here. Here goes...
GOAL:
I want to build a responsive breath controller (BC) circuit using a MPX2010GSX pressure sensor, an op amp, and some other components to adjust the gain and offset. This circuit will connect to keyboards with a Yamaha-BC-compatible input. I'm hoping the project will be a good learning experience for myself and others. I'll build a working prototype and test, and do what I can (with your help) to finish with a final schematic, parts list, mechanical plan for breath tubing, and clear instructions with a wiring diagram that will be shared with other keyboardists seeking a DIY Breath Controller project.
BACKGROUND:
As a trombonist, I find that playing a keyboard with a breath controller feels very intuitive and expressive. Yamaha made the BC-1, BC-2, and finally, the BC3a breath controller-- which was discontinued in 2011. These connect to the BC inputs found on yamaha, kurzweil and other keyboards. Currently, used Yamaha BC's are rare, expensive and maybe unsanitary :P A few companies are selling very expensive BC's that will work with USB, MIDI, or BC inputs. Based on the interest I've seen on forums and in a petition to Yamaha to bring back the BC3, I believe there is a substantial number of BC enthusiasts who would love to have a DIY plan to make a compatible BC of their own for a small fraction of the cost. I find that my current knowledge is insufficient, and I need your help.
RESOURCES I HAVE NOW:
1. eagerness to learn
2. specs & schematics from Kurzweil for their BC input
3. MPX2010GSX pressure sensors
4. datasheets for sensor & possible op amps
5. schematics for Yamaha BC1 and BC2 (can't find BC3a, the last/best)
6. breadboard, connectors, resistors & pots (from Radio Shack electronics lab)
7. multimeter, soldering iron, soldering skills & basic knowledge.
WHAT I (THINK I) NEED:
1. guidance with designing circuit: "soup to nuts"
2. guidance with choosing component(s)- op amp, resistors/pots, caps, etc.
3. some idiot-level wiring instructions, and other helpful hints.
BC INPUT
The BC input on the Kurzweil K2661 is compatible with Yamaha BC1, BC2, and BC3. It is a 3.5mm stereo jack that: provides -15.32 V on tip, expects a range of -0.5V to -8.5V from BC on ring, sleeve is ground. The suggested maximum current load for the BC input is 20mA.
MPX2010GSX SENSOR:
Accepts 10-16V supply, outputs a range of 1-24mV, only draws 6 mA. Datasheet linked below.
http://www.mouser.com/ds/2/161/MPX2010-256329.pdf
YAMAHA BC1 & BC2:
These appear to use a sensor and op-amp, and are powered by the BC input. The BC-1 circuit is from a CS-01 synth schematic. The BC2 schematic isn't sourced.
http://www.jonstubbsmusic.com/misc/yamahabc1.jpg
http://www.jonstubbsmusic.com/misc/yamahabc2.gif
KURZWEIL K2661 BC CIRCUIT SCHEMATIC:
http://www.jonstubbsmusic.com/misc/k2661bcschematic.jpg
ADDITIONAL INFO FROM KURZWEIL ABOUT THE CIRCUIT:
"The breath control jack, J708, is designed to interface with a Yamaha breath
controller. This is an active device containing an op-amp and semiconductor
pressure transducer. The active circuitry is powered by a negative voltage
magnitude greater than -8 volts supplied through the tip contact of the 1/8
inch mini jack. This is supplied from -15V through R72 and C40.
The output voltage of the breath controller appears on the ring connection and
ranges from -0.5 volts for no breath pressure to about -8.75 volts for
maximum breath pressure. Op-amp U10-7 inverts this range and offsets it
(R64) for a 0 to +5V range into the processor's A-to-D converter input. R71
and Shottky clamp diodes D23/D24 prevent overdriving of the A-to-D
converter's input.
[EDIT: NEW INFO FROM KURZWEIL SUPPORT--
"The Breath input jack supplies -15V through a 220 Ohm 1/8 watt
resistor to the Tip connection. The maximum safe current is 23.8mA.
Suggested maximum is 20mA. This should be enough to power
several standard op-amps."]
Breath controller insertion detection is through the jack's tip contact. When
not plugged in, -15V from that contact will be divided through R74 and R73 to
approximately zero volts for BRTHSNS. When plugged in, R74 is disconnected
and R73 pulls this signal up to +5V.
The breath control jack and control pedal #2 jack share the same A-to-D
converter input. U10-1 inverts control pedal #2's signal with a slight gain
then sums it with the breath control signal in U10-7. Generally only one
jack at a time should be used. However it is possible to use pedal #2 to
set a variable "minimum" control value when the breath controller is not
being blown into which may be useful."
CURRENT DRAW TEST ON BC2:
Thanks to Chuck White for this additional info:
"I measured 8ma of supply current to the BC2 in the static state….no breath applied. I see no reason that it would change significantly with breath applied but I can’t easily measure the current with the BC2 assembled….or apply breath with it disassembled. The output of the BC2 is a voltage which in the Wind Machine is connected to an op amp so there is essentially no current drawn from the BC2 output into the Wind Machine."
THANK YOU (even for reading all this!!)
obiwanjacobi:
I would just wack it together on a bread board. Start with the BC1 and see how it goes. Then perhaps expand to the BC2. Buy/get some different sensors and opamps and experiment...
Would also be fun to build a BC-input to MIDI converter as a follow-up project... 8)
eevlurker:
I use this and it works great.
http://www.tecontrol.se/products/uni-midi-breath-controller
It is a breath controller with both USB and MIDI DIN outputs. It works with either a computer or a synth (standalone with a synth, as long as it is powered through the USB connector). There is also a USB only model, for those who use virtual instrument plugins on computers: http://www.tecontrol.se/products/usb-midi-breath-controller
There are some interesting videos on YT, for example
happyrat1:
Perhaps I can shed a bit of light on this.
Both stubbsonic and myself are owners of Kurzweil Keyboards and members of a Kurzweil forum where this discussion began.
One great feature of the Kurzweil is that it possesses a native breath controller port that is plug compatible with the BC2 and BC3A from Yamaha.
Regrettably Yamaha discontinued production of the BC line a few years ago leaving us with tacky addon MIDI breath controllers and other kludges, or else the option of buying used (yuck!) breath controllers on Ebay.
Recently a new company named Kelfar Technologies has announced the BCK-1 which it claims is plug compatible with the BC3A. Unfortunately it is priced at $199 USD.
http://kelfar.net/BCK-1.htm
What stubby and I are trying to do is reverse engineer the BC3A and whomp up home brew units for under $40 USD which is the max value of the necessary parts.
Our main snag is lack of tech info from both Kurzweil and Yamaha as to what the exact specifications should be.
Since these Kurzweil keyboards cost well over $2000 new we're treading as cautiously as possibly so as to not brick our boards with a home brew experiment.
One might assume that the BC2 schematic is straightforward enough, but as stubby mentioned, we have no idea of the max and nominal current load of the Kurzweil's BC port and therefore are flying somewhat blind.
Myself, I took a few electrotech courses back in college three decades ago and my knowledge is hopelessly rusty and out of date. While I can still read a schematic and assemble a protoboard as well as the next guy, my design skills are nowhere near up to today's standards.
If I were to guess, I'd imagine we'd be safe if we kept current loading below 20 mA max, but I'm not even certain of the polarities of the current ranges required or whether or not we'd have to invert the output of the pressure sensor we've decided to go with.
Myself, I have other life issues to deal with which will probably keep me from attacking the problem with a proper test bench setup for at least another year from now, but stubby is all gung ho about building one now.
At any rate, neither of us wants to spend $200 plus shipping plus taxes for what amounts to a simple piece of gear containing about $15 worth of parts and realistically worth about $60 retail.
If anyone out there could whomp up a proper schematic suitable for assembly on a perf board in a project box, we, and the entire Kurzweil community would be eternally in your debt.
Thanks for listening,
Gary ;)
Andy Watson:
--- Quote from: happyrat1 on November 14, 2015, 04:55:15 pm ---Our main snag is lack of tech info from both Kurzweil and Yamaha as to what the exact specifications should be.
One might assume that the BC2 schematic is straightforward enough, but as stubby mentioned, we have no idea of the max and nominal current load of the Kurzweil's BC port and therefore are flying somewhat blind.
--- End quote ---
As you say, you need more information. I would start with, say, a 10k pot across the power pins and wiper to the control signal pin of the input to your Kurzweil. Use a DVM to map-out the response of the Kurzweil. I see the OP has already mapped the expected output.
Then, as suggested above, I would "wack together" the BC1 circuit. Directly substitute the MPX sensor for the IT43904. I suspect the circuit will require more gain to function properly - but suck-it-and-see will be the easiest option. (perhaps that should be blow-it-and-see :) )
As for the power supply - the partial schematic of the Kurweil shows that the -9V supply is protected by a 100 ohm resistor - so you have 9 volts available at a source resistance of 100 ohms - make of that what you will - with the right sensor it should be possible to obtain a working system.
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