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maximum voltage input for PIC16F877 ADC input..

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bb

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pic16f877a voltage

can someone tell me what is the maximum input voltage for PIC16F877 10bit ADC? i'm using PA2 as single input.. thx
 

bb

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maxmimum pic adc input voltage

i have connected the 8bit output of ADC to portD. by the time i input DC voltage around 1 to 2 volts, all the LED is light up.. is it the maximum voltage that supply to ADC is less than 2V?
 

dpsman

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pic16f adc vref

Max Vdd = 5.5V
Max voltage in analog pins = Vdd + 0.6V (according to the analog input model)
 

VVV

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pic 16f877a adc max voltage

The maximum input voltage is 5.5V. That is what the pins can withstand without damage.
What you are describing sounds like you are getting too high readings for the voltage you applied. That makes me ask:
What is the reference for the A/D? Did you configure the reference input correctly?
 

bb

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adc input

i have test out the ADC input with applying DC voltage from power supply. when i adjust around 2 volts.. all the output LED are light up.. is my testing on ADC input wrong? :( A problem i see from my testing is without supplying any voltage input to PA2, 2 LED are already light up..
 

IanP

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pic vref max voltage

There is nothing wrong with your tests, but ..
At RA3 and RA2 pins you have Vref(+) and Vref(-) or you can select Vref(+)=Vdd and/or Vref(-)=Vss.
As VVV asked before, have you checked the Vref?
Regards,
IanP
 

bb

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pic16f877a handling analog inputs

i have set ADCON1=80H.. according to datasheet, this is to set all PORTA pins to analog input.. do i still have to find out the +Vref and -Vref? how am i going to do that? TQ.. :eek:
 

IanP

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pic16f877 max vref

In the data sheet you can find a table on the ADCON1 register.
Tis table will give you information on what bits you have to SET or CLEAR to connect Vref(+) to Vdd or pin RA3 and Vref(-) to Vss or RA2. There are 4 bits responsible for thes options: PCFG3, 2, 1, and 0.
The easiest way will be to select option where Vref(+) goes to Vdd and Vref(-) goes to Vss. In this case you will have the range set by the supply voltage.
Otherwise you will have to connect external Vref to RA3 and set Vref(-) to Vss (if you want to use single-ended inputs).
Regards,
IanP
 

tarts

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but what about digital inputs. I need to detect if supply voltage is present. It may vary from 4.0 to 15V. If I'll make a voltage divider then at 4V the input is not high enough to detect HIGH voltage. Could I just add maybe a 1MOhm resistor in series to limit the current and connect it to 15V. or is the voltage that mathers?

Thanks!
 

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