On Thursday, March 13, 2014 8:48:40 AM UTC-6, cagri yilmaz wrote:
>
> I used for AIN1 (P9-40) connected a PTC with parallel 480 ohm resistor and
> P9-03 3.3V and P9_34 AGND. I did not used VADC P9-32 as reference. Is there
> anybody knows what I did wrong?
>
Oh oh... The absolute maximum allowed input on ANIx is 2.1 V per the AM335x
datasheet. You may have damaged your CPU by connecting to 3.3V.
The PTC should be used to form a resistor divider between VADC (P9-32) and
GND_ADC (P9-34). The voltage out of the divider will change as the value of
the PTC resistor changes. See the crude schematic below.
VADC
\
Fixed Resistor
/
AIN1
\
PTC
/
GND_ADC
AINx will always be less than VADC and greater than GND_ADC.
HTH
Dennis Cote
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