ADC

[npascher]

Hey all,

I have got some questions on the ADC of the Demop Board.

1. The measurement range goes from 0...3.3V?
So it is not possible to measure negative voltages directly?

The second theme is, my oscilloscop shows me a really smooth voltage value, but the value measured by the Demo Board, and ploted in Scilab (Communication via USB ) is not as smooth as the oszi value.
I got some peaks at about 0.25V while measuring a value around 2.5V
If I pull the ADC against ground I recieve a nice smooth line in my Scicos.

I even let the dsPIC produce a sine signal and send it to the PC to ensure the USB communication works without noise. The sine signal is smooth.

I guess I get the noise because I have two different grounds.
The signal, I would like to measure, has another ground than my µC. Is it possible to plug the the ADC to an extern reference point (ground)? If I take a look in the technical data sheet of the Demo Board, I just can see the Analog Input 19, Analog Input 20 and Analog Input 21 with the pins 9, 18 and 20. What is the reference point?


Kind regards,

Niko

[paolo.gai]

Dear Niko,

- the measurements goes from 0 to 3.3. If you need negative values you\'ll need to add some hardware to change the voltages.

- It is possible to put an external reference, which is selectable from the two jumpers JP6 and JP7 next to the microcontroller. You can select either the 0 reference of the microcontroller or an external reference

- but I do not remember which reference must be selectable from the demo board (I do not have a demo board to try it now)

Btw, do you have the schematics? they should be in the CDRom. If you do not have them just send a mail I\'ll send to you directly.

Paolo