[sdiy] More on adding analog ins to digital

[xamboldt]

OK - it works now. Sorry for taking up the bandwidth. It's a cool mod,
though - if I apply it to the other pots on this controller, I can have up
to a 12-channel CV to MIDI/MIDI over USB converter! I'm not sure what the
resolution is, but it's a "free" (or at least cheap) bonus so I'm not
complaining!

-Chris

PS powering the controller from the USB bus is a little iffy (OS X shuts
down the USB port if too much current is drawn, which happened a few times
during testing, but seemingly can be avoided if one is careful about
plugging and unplugging patch cords).

On 10/28/05 12:53 PM, "xamboldt" <xamboldt at earthlink.net> wrote:

> It seems that I don't realize what goes wrong with these things until I
> publicly post what the problem is, and am forced to embarrass myself in
> "public" (does this count as public?) by stating what the real, and
> typically obvious, problem is. In my haste to do the mod, I believe I hooked
> the jack up backwards - that would explain the symptoms I'm experiencing.
> I'll crack the thing open again later and fix that and see what happens...
> 
> -Chris
> 
> 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.
>>>> 
>>>> 
>>>> 
>>>>    
>>>> 
>>> 
>>> 
>>> 
>>>  
>>> 
>> 
>