Assume you have are using your processors 12-bit ADC to read the voltage divider

Question

Assume you have are using your processors 12-bit ADC to read the voltage divider. See the diagram and answer the following five questions below it:

High Voltage R1 1Meg ADC R2 10K 1. With an internal Vref+ of 2.5V and a Vref- of 0V. What is the Maximum High Voltage that can be measured? 2. What is the High Voltage resolution that can be measured? 3. What is the ADC hex value for a High Voltage of 230 volts? 4. What is the ADC hex value for a High Voltage of 1 10 volts? 5. Could you set an alarm if the High Voltage of 230 varied by +/-190?

Explanation / Answer

Solution:

Maximum resolution = 2.5/212 = 0.610mV

For 230V, VADC = (10K/1010K)*230 = 2.2772

2.5V corresponds to 0xFFF

4) ADC takes the positive values and ADC conversion is in straight binary form

For 110V, VADC = (10K/1010K)*110 = 1.0891

2.5V corresponds to 0xFFF

1.0891 is equal to in hex = 0x6F8 in hex

5) If high voltage of 230V is varied by ±1%, VADC is changed by ±0.022772 which is more than the resolution of the ADC. So, the alarm can be generated.

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