230VAC voltage measurement with Atmega / Arduino optoisolation

Hello

I would like to build the simplest system that allows measuring AC voltage in the socket, so that I can read it through the ADC converter in the Atmega8 microcontroller. I want the system not to have a transformer. I would also like to have galvanic separation. At the moment, I was able to come up with something like this:



Resistors R15 and R16 are 2W and have 100kOhm each.
P8 leads to the ADC input of the microcontroller.

Is it possible to measure AC voltage with an accuracy of ~ 5V through this system?

wojtek6000 wrote:

circuit enabling the measurement of alternating voltage in the socket

If it's alternating.

wojtek6000 wrote:

Is it possible to measure AC voltage with an accuracy of ~ 5V through this system?

No.
I don't know why this 100uF capacitor. Charging via a 4k7 resistor will take a long time ...

Hmm ... what if I gave up optoisolation and left only R15, R16 and diode? It won't be safe for a microcontroller, but will I get the desired effect then?

You should not give up galvanic isolation. It can also be dangerous for the programmer and the computer, ending with you.

Galvanic separation using a tiny transformer is strongly recommended here.

So the solution that allows for a "fairly accurate" measurement of 230V alternating voltage is the system from the attachment? The resistor and capacitor would have to be selected depending on the transformer used.

wojtek6000 wrote:

So the solution that allows for a "fairly accurate" measurement of 230V alternating voltage is the system from the attachment?

No. The circuit from the attachment measures DC voltage and not AC voltage. Why did you give diodes and a capacitor? To measure alternating voltage?

Use one of the transformer terminals to ground the microcontroller circuit, from the other lead the diode in the direction of conduction to the microcontroller. Behind the diode, give a resistor divider so that it has a voltage drop on it that will not kill your microcontroller (0-5V + surge supply). With this system you will be able to make single-phase alternating voltage measurements. So with a diode you cut off the positive part of the sine. It is then easy to measure the frequency, effective and maximum value.

Is this system correct so that I can measure the RMS voltage? I know that I will have to add a piece of code that calculates it, but I can handle it

I think it will do. The pin which you marked ADC is best checked with an oscilloscope before connecting to the microcontroller. If it does not exceed the permissible voltage, it will be ok. To be sure, you can still give a 470Ohm resistor in series, followed by a zener diode opposite 3.6V or 5.1V. This will protect your circuit against overvoltages, however, it can introduce distortions in the measured signal.

I was able to design the system and write a program to measure the effective voltage from eight channels with the help of an analog multiplexer CD4051B. In another thread I found information that in order to determine the rough value of the effective voltage you should multiply the peak voltage by the square root of 2. So I did. However, I have a problem. The system without connecting any test leads indicates correctly 0V, but after connecting the cable with 230VAC voltage to one of the eight TEZ 1.5 / D 230/6 transformers, the system reads at the 169V input, and on other unconnected it indicates about 16V. What could be wrong? Below is the program and circuit diagram (resistors in the dividers are 4.7k).

[code:1:d5ce73d7f3]

#define WA A1
#define WB A2
#define WC A3

void setup() {
// put your setup code here, to run once:
pinMode(A0,INPUT);
pinMode(WA,OUTPUT);
pinMode(WB,OUTPUT);
pinMode(WC,OUTPUT);
Serial.begin(9600);
}

/*
* ustawieniee kanału multipleksera
*/
void set_kanal(byte nr){
switch(nr){
case 0:{set_0();}break;
case 1:{set_1();}break;
case 2:{set_2();}break;
case 3:{set_3();}break;
case 4:{set_4();}break;
case 5:{set_5();}break;
case 6:{set_6();}break;
case 7:{set_7();}break;
default:{res();}break;
}
delay(20);
}

void set_0(){
digitalWrite(WA,LOW);
digitalWrite(WB,LOW);
digitalWrite(WC,LOW);
//Serial.print("Odczyt z zero:\t\t");
}

void set_1(){
digitalWrite(WA,HIGH);
digitalWrite(WB,LOW);
digitalWrite(WC,LOW);
//Serial.print("Odczyt z jeden:\t\t");
}

void set_2(){
digitalWrite(WA,LOW);
digitalWrite(WB,HIGH);
digitalWrite(WC,LOW);
//Serial.print("Odczyt z dwa:\t\t");
}
void set_3(){
digitalWrite(WA,HIGH);
digitalWrite(WB,HIGH);
digitalWrite(WC,LOW);
//Serial.print("Odczyt z trzy:\t\t");
}
void set_4(){
digitalWrite(WA,LOW);
digitalWrite(WB,LOW);
digitalWrite(WC,HIGH);
//Serial.print("Odczyt z cztery:\t\t");
}
void set_5(){
digitalWrite(WA,HIGH);
digitalWrite(WB,LOW);
digitalWrite(WC,HIGH);
//Serial.print("Odczyt z piec:\t\t");
}
void set_6(){
digitalWrite(WA,LOW);
digitalWrite(WB,HIGH);
digitalWrite(WC,HIGH);
//Serial.print("Odczyt z szesc:\t\t");
}
void set_7(){
digitalWrite(WA,HIGH);
digitalWrite(WB,HIGH);
digitalWrite(WC,HIGH);
//Serial.print("Odczyt z siedem:\t\t");
}
void res(){
digitalWrite(WA,LOW);
digitalWrite(WB,LOW);
digitalWrite(WC,LOW);
delay(5);
}

double get_voltage(){
long czas_start=millis();
long teraz=0;
int _max=0;
int pomiar=0;
while(teraz_max){
_max=pomiar;
}
}
return map(_max,0,1024,0,240)/sqrt(2); //obliczenie watości skutecznej
}

void loop() {
for(byte i=0;i