I’m a EE major who is designing a wireless touch-plate keyboard for use with modular synthesizers as my senior design project.
I’m using the IEEE 802.15.4 Zigbee protocol with a ti msp430 ucontroller but i’m having a hard time with the design of the touchplate keyboard.
I understand that most modular synthesizers use the 1V/octave standard but i have been unable to find information regarding the design of touch-plate control voltage keyboards or any CV keyboard design which interfaces directly with the inputs of VCO’s, VCF’s and VCA’s.
I just want to design a circuit which will control the pitch of a VCO without the need for a MIDI to CV converter.
The only touch-plate design circuit i have found so far is John Simontons touch switch circuit he used for his Programable Drum Set.
Any advice would be greatly appreciated since i only have 6 weeks to finish the design.
Thanks,
theglyph
There are a million touch plate designs out there.
I recently built one into a Musonics Minimoog, so when you touch the Minimoog nameplate, the clear mod wheels light up.
Many TP designs rely on you being grounded or closing two sets of contacts.
Obviously this isn’t ideal for your needs. However, they are the most reliable types. Others take the AC component from your body and use it to switch a circuit. Some do it by rectifying this signal and charging a cap, then using a basic comparator to decide the trip point, this going to either a one-shot or a flip flop.
Having a type like this can be useful because the time that your finger is on the pad is entered into the equation. You don’t want false triggering.
The type I built used a 555 and a flip-flop to do all the dirty work.
The touch plate varied the PW of the 555 (duty cycle) and the on to off ratio of pulses charged the cap. Like I said, there’s a million ways to do this.
Keep in mind that a capacitance/body hum type of sensor actually works poorer for people that are grounded and can be susceptible to power line spikes and other spurious signals. For one that works well when you are grounded, you might obtain the Oberheim OB-1 schematics. They used a touch switch circuit for their program changes. Also Serge and Buchla schematics are around with workable circuits.
Hope some of this helps.
Thank’s Kevin,
I’ve worked with the 555 setup as you described but it dosn’t seen to work the Way i had hoped! It’s tricky and i’m running out of time!
Thank you so much for the reply because i thought i was alone on this issue!
You would be surprised at some of the info i have received regarding a wireless touch-plate keyboard.
i’ll try to use your advise and hopfully things will work well!
Best Wishes,
theglyph
I quickly made a schematic from the handdrawn scribbled notes I still had on this.
I didn’t include an opamp and cap for the LED “grow/dim” feature, but this is the same circuit I used for the Minimoog wheel lamps.
Minimoogs being 10V systems, this one is too. 
Try here: http://www.synthfool.com/schematics/touchplate.gif
See if this helps out.
Shielded wire to the TP helps.
