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Old 03-25-2016, 06:56 PM   #1
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Posts: 3
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Default PIC32 MX795F512L - ADC problem

I made a custom board based on Microchip MEB (DM320005) and PIC32 Ethernet Starter Kit that use the MCU in subject.
My board has a touch screen that works fine, connected to AN11 AN12 AN13 and AN14.
The internal ADC10 of the pic convert the analog signal to X and Y position.
My board is powered by a Li-ion battery 3.7V and I need to know the battery voltage to have simple indication of the battery state, so I connected the battery to AN2 through a voltage divider.
I'm using the microchip touchscreen driver included in microchip framework V. 2013-06-15.
My problem is I cannot get the correct value of the adc for the AN2 channel. To do some tests I used the code below, took from the Microchip ADC reference:
void ReadBatteryAdc()
    //disable timer 4
    T4CONbits.TON = 0;
    TRISBbits.TRISB11 = 0;
    TRISBbits.TRISB12 = 0;
    TRISBbits.TRISB13 = 0;
    TRISBbits.TRISB14 = 0;
    TRISBbits.TRISB2 = 0;
    LATBbits.LATB11 = 0;
    LATBbits.LATB12 = 0;
    LATBbits.LATB13 = 0;
    LATBbits.LATB14 = 0;
    LATBbits.LATB2 = 1;
    AD1CHSSET = 0x0020000;

    AD1CON1 = 0;            // reset
    AD1CON2 = 0;            // AVdd, AVss, int every conversion, MUXA only
    AD1CON3 = 0x1FFF;       // 31 Tad auto-sample, Tad = 256*Tcy
    AD1CON1 = 0x80E0;       // Turn on A/D module, use auto-convert
    AD1CSSL = 0;            // No scanned inputs

    AD1CON1bits.SAMP = 1;
    while(AD1CON1bits.DONE == 0);
    vBitLevel = ADC1BUF0;

    //enable timer4
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Old 03-27-2016, 11:29 AM   #2
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Are you running the MCU directly from the battery or through a LDO regulator?
The reason I ask is that you are setting AD1CON2 such that it will use AVdd as Vrefh and AVss as Vrefl.
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