analog to digital general question

mishell .g · Guest

Hi
I have a good experience with pics but I need to do one simple thing that I don't know how: using the A\D.

I need to take external analog input to pic16f88/7 and check what is the binary number for that voltage. For example I need to input 4.2v and put the binary number of it in an integer (get the number to my software).
After that, to check if this integer is bigger then some other integer that I define (with the A\D of the pic16f88).
How do I get the binary number from analog input ? How is it represented ? Floating point ? What code required by the A\D ?

I will be more than happy to get example code for getting a number.

Thank you a lot.

Guest · Posted: Fri Oct 17, 2008 7:54 am

There are several examples programs for using ADC supplied with the compiler. May not be specific to the 16F88 but should work the same way. Take a look at those examples.

mishell · Guest

Yes there is help file for everything but that wasnt my question.

i need to know how a fraction is presented by the chip ?
i need to check if the analog input is bigger then 4.25 so how do i write the number 4.25 in hex ?? floating point?

can someone give me example of how to check if a volatge is bigger then 4.25 ?

value=read_adc()
if (Value> ??????????? )
.
.

Guest · Posted: Fri Oct 17, 2008 10:54 am

According to the data sheet, the 16f88 has a 10 bit ADC, and is a 5V part. This means that the PIC can measure voltages from 0V to 5V, with 10 bits of resolution. The digital value will be a 10 bit binary number. 5V corresponds to 0x3FF, or 1023. 0V corresponds to 0x000. To calculate a given voltages digital value, use this equation:

Digital Value = (Given Voltage *1024)/5V

So the value for 4.25V will be 870 (the actual value is 870.4, but the adc can't resolve 870.4, only 870 or 871.)

mishell · Guest

Thank you , it hepled a lot.

i just didnt understand-how do i present a number in software??
i cant just write 870 (=4.25v) ... ??
so how this 870 is writen? what are all the ways to write that?

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

See this example program:
http://www.ccsinfo.com/forum/viewtopic.php?t=32168&start=1

Guest · Posted: Sat Oct 18, 2008 7:09 am

thanks but it wasnt my question,

how do i present a number in ccs in hex?
lets say 870- how do i write it?

to compare to numbers:
value=read_adc()
if (value> ??????? ) // ???? = 870

dyeatman · Joined: 06 Sep 2003 Posts: 1924 Location: Norman, OK

The link PCM gave you was EXACTLY your question:

mishell · Guest

I get error on ' setup_adc_ports(AN0); '
why is that?? is this code good generally?
thanx!

dyeatman · Joined: 06 Sep 2003 Posts: 1924 Location: Norman, OK

If you look in the 16F88.h file it shows the line should be:

Guest · Posted: Sat Oct 18, 2008 8:11 am

yes i was seen this after i posted this...
thank you.