16F877A with ADC function, how??

[No_Fear]

Hi there,

I never played with 16F877A, and its adc function.Now i should measure voltage between -5V and +5V.I need to use all 8ch for my project.I saw +Vref and -Vref is also analog channels.How will i use them both Vref and adc channel? Is there any project created with ccs? I can't find any sample codes and projects about this simple project? Can you advice me something?? Thanks.

No_Fear
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This message was ported from CCS's old forum
Original Post ID: 12739

[R.J.Hamlett]

:=Hi there,
:=
:=I never played with 16F877A, and its adc function.Now i should measure voltage between -5V and +5V.I need to use all 8ch for my project.I saw +Vref and -Vref is also analog channels.How will i use them both Vref and adc channel? Is there any project created with ccs? I can't find any sample codes and projects about this simple project? Can you advice me something?? Thanks.
:=
You will have to scale your input voltage to be between 0v, and 5v. A simple op-amp 'adder', with 5v as the second input, combined with a division by two, will give you a signal where -5v, arrives at the PIC as 0v, and +5v, arrives as 5v. You cannot use the pins as signal inputs, and as voltage reference inputs, but even if you could, you would still need to use the op-amp offset, since the refernce inputs, cannot go to -5v. The input range for all the PIC pins, is only 0.3v, each side beyond the incoming supply voltage.

Best Wishes
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This message was ported from CCS's old forum
Original Post ID: 12745