AC Voltmeter Using Microcontroller Design help

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Thread Starter


Joined Apr 9, 2018
Hello Friends ,

I have gone through lot of post on how to design AC voltmeter using pic micro-controller (PI16F913) . I am doing it for one of my project. I want to design a digital voltmeter which can measure from 80 VAC to 160 VAC (RMS Values only). I cannot use a potential transformer because of limited space. What I want is that the meter is powered form the same input AC source which it is measuring. I have used a Full wave bridge rectifier & a 330 micro-Farad Cap to convert 115v AC to 115 V Dc. & a potential divider to bring to voltage down within 5 Volts for microcontroller to measure. I am using a zener diode voltage regulator with transistor buffer as an input to Voltage regulator (5V output).

I have breadboard the circuit but the problem is that the Regulator output reduces to around 3 vollts when i am setting the input volts through Ac variac
to 90 volts the LCD turns off. I checked the voltage output of the regulator and it was around 2.9 volts which is way less for LCD. ( LCD is a 5V LCD). So how would i solve this problem. Also The ADC Values have lot of variation is there any perticular solution to them?

Here is my circuit diagram.

Thanks in advance.


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