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Hello Guys,
I want to measure the high voltage so i use Voltage dividing circuit and
read adc value but some problem is appear;
then in programe i use vcc for reference;
adc=ADC10MEM;
voltage 1 = adc*3.3/1023; (ADC measure Voltage)
voltage 2 = voltage 1 * (R2+R1)/R1 (VCC VOLTAGE)
it strange then value is not correctly to three-meter;
for emaple 30V -VCC then the result like picture;
note:adc value measure is Equivalent to three-meter
i am see the tutorial for msp430g2xxx series the page552 write max ohm is 2k.ok this is not important
so if norman the resistance is 1k ohm then ,how can explain the voltage .
if vcc=30v then vcc x (R1//1K/(R2+(R1//1K)) = 30 *0.5K/13.5=1.111V then is not equ 1.89V or 2.1V
so where the three-meter measure then get 1.89V???????
Because i used 3.3 ref by adc channel , so the value is 0~1023, so the value mean measure the adc channel value so i need to return the voltage ,so i mul the 3.3/1023 if r1 is 3.3 mean the adc is full then see my circuit the div voltage mean can measure the max voltage 0-35v if vcc×r1/r1+r2 ,the vaule is near 3.3v
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