R1 is chosen so that the current through the winding does not exceed 2mA, it holds a maximum of 10mA, but after 2mA linearity is lost and the output will be clear that.
Step 1: Determination of maximum output RMS voltage
VOutmax is decided by the ADC peak voltage in the sampling loop of Microcontroller.
For Bipolar ADC
As for ± 5V ADC, the maximum RMS voltage of the transformer:
For Unipolar ADC
As for 0-3.3V ADC, the maximum RMS voltage of the transformer:
Step 2: Determination of input current-limiting resistor R1
Vin : Rated input voltage
I ： Rated operating current （ when Coil resistance is compared with current-limiting resistor R1, it can be ignored.）
ZMPT101B usually working at rated current: 1~2mA.
When Rated input voltage ≤ 100V ，Usually choosing the operating current I=2mA; When Rated input voltage ≥ 220V，To reducing the resistor power， usually choosing the operating current 1 mA ≤ I ≤ 2 mA.
for example V=100V，I=2 mA，
for example: V=220V，I=1.1 mA，
To improve reliability, the current-limiting resistor selected usually is greater than its 4 times the rated power, and generally, uses a high temperature coefficient metal film resistor.
Step 3: Determination of the sampling resistor R2
for example: Voutmax =3.53V，Vin =100V
The above formula is also suitable for the two ways of active and passive output.
When selecting the sampling resistor, Resistor should not exceed