ADC Using Vref-

[beambase]

Hello
I am working on a project that requires a 18F4550 to read an analouge voltage between 0.5V to 4.5V. In the ADC component I can only find a settting to use the Vref+ input but nothing on how to enable the Vref- input. Is it possible to modify the ADC compnoent in some way?

[Jan Lichtenbelt]

Dear Beambase,

In the ADC properties you can choose for Vref-option: Vdd or Vref+. By choosing Vref+ you enable this option. Just put Vref+ on pin 5 of 18F4550 and it must work as you wish.

Succes

Jan Lichtenbelt

[beambase]

Hello Jan,
I know about the Vref+ function but I need to set the Vref- to 0,5V so the ADC will work between 0,5 - 4.5 V.
Does anyone else have any suggestions?

[Benj]

Hello,

To allow for Vref- functionality you will have to use the code customisation feature of v4 to edit the ADC sample component macro. The -Vref is simply a bit that is set or cleared in one of the ADCON registers. The device datasheet will show you exactly which bit and register to change and the +Vref bit of code should show you how to manipulate the register.