[sdiy] More on adding analog ins to digital

[xamboldt]

Yeah, the wiper varied between CV and ground based on its position. The
ground from the newly-installed jack is connected to the ground in the
controller, and the CV source grounds are connected to the CV source jacks,
so all the grounds should be connected once the plug is inserted...


On 10/28/05 12:35 PM, "Seb Francis" <seb at burnit.co.uk> wrote:

> did you measure the voltage out of the pot centre wiper?  is it what you
> would expect? (varying from GND up to the CV voltage)
> 
> you did connect the GNDs of the CV source and the controller, right?
> 
> xamboldt wrote:
> 
>> Back in July, there was some talk on the list about wiring a switched jack
>> to the 5 volt side of a pot in a digital synth, so one could insert a 5 volt
>> CV in place of the voltage normally coming from the pot. This is a brilliant
>> idea, and I decided to try it on an Evolution MK249C MIDI controller I have
>> - hoping to get a CV to MIDI converter out of the deal. I checked the
>> controller, and the pots indeed were between ground and +4.6 volts or so.
>> 
>> So I disconnected a pot from the internal 5v, wired the switched lug of the
>> jack to that 5v signal, and then wired the tip lug from the jack to the lug
>> of the pot where the 5v signal used to go.
>> 
>> I tested it: If I have nothing plugged in, the jack is normalled to +5v, the
>> control works as it did before the mod. However, when I plug in a 5v CV from
>> the outside world, nothing happens at all. I used the pot as an attenuator
>> to make sure I didn't throw too much voltage at the circuit, but even with
>> it all the way up nothing happens (and only using a CV source that maxes out
>> at 4.9 V). 
>> 
>> I added a diode to the circuit to protect it from negative voltages (anode
>> to ground, cathode to the +V side of the pot), but it doesn't seem like this
>> would be affecting the operation of the circuit if I'm sticking to +V
>> sources.
>> 
>> Any ideas on what's going on here? I checked for wiring mistakes and
>> everything seems right (it would have to be hooked up correctly for the
>> normalled signal to work, right?) - it's not a very complicated mod to do -
>> or so it seemed...
>> 
>> -Chris
>> 
>> 
>> 
>>  
>> 
>>> I found the same arrangement in an Evolution UC-16.  I plan to do the same
>>> to get CV to MIDI and USB.
>>> Larry Hendry
>>> 
>>> -----Original Message-----
>>> From: owner-synth-diy at dropmix.xs4all.nl
>>> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Grant Richter
>>> Sent: Friday, July 15, 2005 10:05 AM
>>> To: Rainer Buchty
>>> Cc: synth-diy at dropmix.xs4all.nl
>>> Subject: [sdiy] More on adding analog ins to digital
>>> 
>>> 
>>> I opened up a Yamaha DJXIIB and traced out the front panel controls.
>>> 
>>> The pots are between 0 to 5 volts. They must run to a multiplexor and
>>> be converted with an A/D.
>>> 
>>> I added a series of switched jacks to the +5 volt side of the pot so
>>> that I could insert an external voltage to replace the 5 volts. This
>>> seems to work fine and the pot can be used as an attenuator.
>>> 
>>> This spoof may work for other digital boxes that have faceplate pots,
>>> but not for encoders.
>>> 
>>> 
>>> 
>>>    
>>> 
>> 
>> 
>> 
>>  
>> 
>