This in in relation to a MIDI knob box. All requirements should be similar
to a standard Data Aquisition system but only 7-bit accuracy is required
(would like to be able to scale up to 14bit at a later time tho), doesn't
matter what you do to the input as long as values from 0-127 are outputted.
As it's MIDI any noise is fine as long as the 0-127 range is maintained with
fair linearity.

What I am trying to do is create some sort of automatic voltage scaling
system. The device is intended to be usable by electronically illiterate
persons so no big words\concepts can be needed by the end user. Effectively
I would like a system whereby you can plug any voltage into the box and it
will detect the voltage range allowing it to auto calibrate itself for that
input.

The sort of process I had envisage was as follows:
1. User inserts voltage to calibrate for into special calibration input.
2. This input has a fuse rated at the maximum voltage the system can handle
without blowing up. There would be an LED after the fuse so if it doesn't
come on you know the voltage was real bad. Ideally the system would be able
to handle a fairly high voltage (e.g. 20V +) so they are very unlikely to
blow the fuse.
3. The system would then in some way get the input voltage down to the range
the ADC could handle.

I have no idea if this is really possible in any meaningful way but it would
be pretty useful so I will give it a go.

I had the following idea for achieving the actual scaling:
1. At this point we know the voltage is less than the fuse voltage (oh well,
say fuse voltage + 5V for safety).
2. The voltage is then fed through a voltage divider created with a couple
(maybe only 1 is needed) of digital pots. At first this would be set to the
maximum possible division to get the voltage as low as possible. Then the
amount of division would gradually be decreased until the resulting voltage
was at ythe upper limit of the ADC. The digital pot values would then be
stored so that the standard inputs (which don't have any extra circuitry for
voltage detection) can be calibrated for that input.


Is this actually possible in this way? Is there a better way to do it?
Ideally no extra components other than the digital pots would be needed
allowing the circuit to be fitted to all inputs (obviously some circuitry is
needed but the less the better). Even better would be to do it after MUXing
as then only one is required but then the MUX must be able to handle the
full input voltage.

Thanks,
Tom.