Yes that is correct. My old measurements shows a safe value area between 2.8V and 5V for a PIC supplied at 5V. If you can't see changes in displayed voltage values when you change the Vref, either you have used in a wrong way the library or it's a problem with the library itself. Check again if indeed the Vref channel is selected and the result is right justified. If you have left justified set and read only the ADRESL, you will loose some resolution. ADCON1 = 0b_1xxx_0100
On 10/25/09, savageio <[email protected]> wrote: > > > Hi Vasile, > > I thought I could set the voltage on AN3 to a value lower than 5 > volts. From the datasheet (39582b.pdf, TABLE 17-14), I think the value > should be between 2,5 and 5,3 volts? > > > > On 25 okt, 18:45, vasile surducan <[email protected]> wrote: > > Hi Savageio, > > > > How much do you expect you can modify the vref value? > > > > On 10/25/09, savageio <[email protected]> wrote: > > > > > > > > > > > > > Hello List, > > > > > I am trying to measure voltage levels of two IR photodiodes. The > > > voltage varies from about 0,2 to 0,5 volts. > > > > > My device is 16F873A. > > > > > I have following ADC setup: > > > > > ----------- code start ------------------- > > > const bit ADC_HIGH_RESOLUTION = low > > > const byte ADC_NCHANNEL = 3 -- 2 analog channels on AN0, > AN1 > > > const byte ADC_NVREF = 1 -- VREF+ is AN3 > > > include adc > > > adc_init() > > > ----------- code end ------------------- > > > > > The photodiodes are connected to AN0 and AN1, and I have a 4K7 > > > potmeter as voltage divider on AN3. > > > I am showing the values from adc_read_low_res(0) and adc_read_low_res > > > (1) on a LCD. > > > > > The vref does not seem to be working as I expected, it makes no > > > difference how I set the potmeter, the values I read are always the > > > same (in a range of 12 - 22, so that fits when vref+ is vdd) > > > > > What am I missing? > > > > > TIA, > > > > > Sander > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/jallib?hl=en -~----------~----~----~----~------~----~------~--~---
