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Pic 16f877a anlog input error

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saneesh george

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Haii all ..
I have a doubt with analog inputs in pic16f877a....I have designed a temperature indicator using lm35 and pic 16f877a(AN0 pin used) it is working well also.I found a scenario that when we connect any of other analog inputs (AN1 to AN7) to VCC then the temperature reading increasing by 15 degree(ie 150 mv).I measured the voltage at AN0 pin and it not have an increase of 150mv.So the error may be an internal...? How this type of interference occurs. May be this is a simple question for professional...but i am a beginner ...help me
 
You're not allowing the A2D time to settle when you switch channels. and you're feeding the A2D from too high a source impedance.

It's why source impedance is VERY important.

If you connect a pot between Vdd and Vss, and the slider to AN1(or other) then you will see AN0 change as you adjust the pot - it's due to the charge/discharge time of the sample and hold capacitor in the PIC.
 
hey canu plz share the code, coz even i tried to sense the temp and display on LCD but m not getting results.Also then I tried for sensing mains but the same problem persists. Plz help
 
Try using an amplifier circuit like lm324 opamp based non inverting amplifier. connect the temperature sensor to the input and connect the output of the amplifier to the pic16f877a
 
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