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### Topic: CV detection - offsetting negative voltage, scaling? (Read 1 time)previous topic - next topic

#### janklug

##### Feb 01, 2012, 12:03 am
Hey,

I'm trying to read the CV output of my Moog Etherwave Plus Theremin (pitch, volume & gate).
These are the specs:

• Pitch CV: Nominal output is -2.5V to + 4.5V.
• Volume CV: Nominal output is 0 to +10V.
• Gate Output : OFF is 0 Volts and +10V is ON.

For the volume and gate, voltage dividers should work (with two 1k resistors) to bring the signal to 5V, right?

The possible negative output of the pitch CV however scares me..

Cutting off the negative part with diodes should keep it safe, but it would be a shame to lose that part of the range...
Isn't there a nice way to shift (and compress) that to the trusty 0-5V range?

Thanks a lot!

Jan
[can't believe this is my first arduino forum post; have been using these beasts for quite a while now ]

#### ajofscott

#1
##### Feb 01, 2012, 01:14 am
Scale it with resistors then offset to 1/2 VCC. What is the voltage range of pitch?

#### retrolefty

#2
##### Feb 01, 2012, 01:16 am
Quote

• Pitch CV: Nominal output is -2.5V to + 4.5V.

Cutting off the negative part with diodes should keep it safe, but it would be a shame to lose that part of the range...
Isn't there a nice way to shift (and compress) that to the trusty 0-5V range?

A simple op-amp with proper offset and gain configuration can convert -2.5 to +5v to a 0 to +5vdc output. Don't have a circuit design to give you but researching on basic op-amp circuit would be a good start for looking for a solution.

Lefty

#### MusicPapa

#3
##### Mar 25, 2013, 08:54 pm
Jan- Did you ever get something working? I have the same issue, and am more of a musician than electronics hobbyist so though I can build from simple schematics I'm easily overwhelmed when it comes to designing a circuit for a particular use.

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