ComputerVoltageSources

HI All

Given that I'm not an EE or even a decent hobby designer, why is this
calibration such a problem?  Why not use trim pots and the Analog
inputs themselves as follows:

First: Ground the input to be calibrated. (This should ALWAYS be a
constant of 0 right?)

Second: Run a small program on the modules CPU to continously return
the value of the converters input via the serial port to a 'telnet'
session on a PC or Mac, followed by a Carriage Return and a Line Feed.
 (This will give you a continous dump of the converters value down the
screen.)

Third: Adjust the timpot until you get 0.00... as the returned value,
and it stays that way for a minute or two.

Would'nt this handle it with NO tools of any kind except those we
already need to use the module anyway?

Larry T.


--- In ComputerVoltageSources@yahoogroups.com, "Grant Richter"
<grichter@...> wrote:
>
> You already have a precision voltage source in your analog keyboard
or MIDI to CV 
> converter.
> 
> The purpose of the calibrated input is so we can read an analog
keyboard input.
> 
> 5.000 volts would be 5 octaves of keys and we can read each key by
it's key voltage.
> That way you can play the keyboard into a sequencer, or use it to
transpose sequences.
> I'm sure there are other applications. You can also read a keyboad
directly via MIDI of 
> course.
> 
> With a 5 volt range, each count is ~5 millivolts, a semitone is
0.083 volts, so there are 
> around 16 counts between semitones.
> 
> Assuming bottom C is zero volts. If your keyboard is only 4 octaves
then calibrate at 4.000 
> volts.
> 
> It is not so important that it be absolute real world voltage, but
it is nice.
> 
> --- In ComputerVoltageSources@yahoogroups.com, "John Loffink"
<jloffink@> wrote:
> >
> > I think you're on the right track.  Use a voltage reference chip,
not your
> > power supply.  Feed this to a high accuracy low voltage offset
differential
> > amplifier with high gain.  Your + and - input resistors are the
ones to be
> > matched.  If both are attached to the voltage reference then the
output is
> > only the difference between the two and the op amp offsets.
> > 
> > John Loffink
> > The Microtonal Synthesis Web Site
> > http://www.microtonal-synthesis.com
> > The Wavemakers Synthesizer Web Site
> > http://www.wavemakers-synth.com
> > 
> > 
> > > -----Original Message-----
> > > From: ComputerVoltageSources@yahoogroups.com
> > > [mailto:ComputerVoltageSources@yahoogroups.com] On Behalf Of
John Mahoney
> > > Sent: Friday, March 24, 2006 8:03 PM
> > > To: ComputerVoltageSources@yahoogroups.com
> > > Subject: [ComputerVoltageSources] resistor matching, was RE:
Calibrated
> > > Inputs
> > > 
> > > Re: matching resistors, will the following procedure work?
> > > 
> > > Ingredients:
> > > 	1 precision voltage reference
> > > 	1 amplifier
> > > 	1 voltmeter
> > > 	Resistors to be matched (RTBM)
> > > 
> > > Feed a small, precisely regulated signal through a voltage divider
> > > made from an RTBM and some other resistor (the "constant"). Feed the
> > > divider's output through the amplifier. Measure the output.
Repeat as
> > > needed.
> > > 
> > > The idea, obviously, is to amplify the differences between the RTBM
> > > so that the voltmeter can register those differences. Concerns would
> > > include temperature stability, power supply stability, etc...
> > > 
> > > So, this may not be good enough for a NASA guidance system, but will
> > > it suffice for this DIY project? As John Lofflink said, we need only
> > > be concerned with relative accuracy.
> > > --
> > > john