ADC reading keep on varies..

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radnusmar

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I use PIC18F4523 and a 4 SEGMENT LED Display module. Both MCU and DISPLAY are connected to same 5V power supply.
A pot(Pin1- VDD Pin2-AN0 Pin3-VSS) is connected to AN0 pin and am able to read & display it in DISPLAY the ADC data.

But my problem is......

When using battery as power supply for the above system,
My ADC readings are stable....

But when using the Linear Power Supply
My ADC readings keep on varying by +4 to -4

When using a SMPS
My ADC readings vary +30 to -30

I want battery like accuracy from a power supply.What power supply should I use?

Thanks in Advance...Please help me out...
 

This is because of noise and ripple.

Place decoupling capacitors across all VDD and VSS pins. Place the capacitors as close to the VDD and VSS pins as possible.

Between the pot wiper and the AN0, connect a 1k resistor. Connect a 1nF-100nF capacitor from AN0 to ground.

At the input and output of your +5V regulator, place decoupling capacitors (10nF - 100nF) in parallel with electrolytic capacitors (10uF - 100uF).

At the output of the regulator, place a bulk capacitor (220uF - 1000uF).

Also, at the input, you may place an inductor in series (between the power supply output and the regulator input). Connect a capacitor (10uF - 220uF) from the regulator input to ground.

Hope this helps.
Tahmid.
 
1. Make the supply stable and ripple free as advised by Mr. Thamid.
2. Does your ADC has an Voltage reference input (Vref). If it does you would like to have that value as stable as possible.
3. Take and average of (say, 1000) multiple readings.
 
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