VOLT METRE - ARDUINO & DIY AMP / WATT HOUR VOLT METER - ARDUINO

Off-grid Ham Radyo ve Güneş projem için volt, amper, watt, amper saat ve watt saatlerini
ölçmenin bir yoluna ihtiyacım vardı. Bunu yapabilecek birkaç ticari ürün var, ama istediğim esneklikle değil. Çok genişletilebilir bir Arduino mikro denetleyici tabanlı çözüm tasarladım.

Şu anda ekli cihazların yukarıdaki değerlerini izliyor ve veri toplamak için web izleme ve
 sd kart eklemeyi düşünüyorum. Peki, başlayalım.




First we visit our friendly Voltage Divider Calculator. I input 20v as the input,

 5v as the output, and 10k for R2 (experiment with
<10k 30k.="" a="" calculates="" get="" likely="" of="" p="" pair="" r1="" resistors="" this="" till="" you="">
R1 = 30k Ohms

R2 = 10k Ohms

Vout = (R2 / (R1 + R2)) * Vin

Vout = (10000 / (30000 + 10000)) * 20v

Vout = (10000 / 40000) * 20v

Vout = .25 * 20v

Vout = 5v

Ratio = Vin / Vout

Ratio = 4

Because the Arduino has a 10-bit ADC, it outputs 0-1023 (1024 steps) for a 0-5v input. That's 0.00488v / step.

With a Voltage Divider with R1 = 30k Ohm and R2 = 10k Ohm, A 12v battery would calculate as follows:

12v / Ratio = 3v on the A4 pin.

3v / .00488 = 615 (ADC Reading - round up)

so A4 pin Voltage = .00488 * ADC reading (615 in this case), or 3.00 volts.

Then battery voltage = A4 pin voltage * Ratio (3 * 4 = 12)

The code to read that value is as follows:

ADCVal = analogRead(batMonPin); // read the voltage on the divider on pin A4
pinVoltage = ADCVal * 0.00488; // Calculate the voltage on the A/D pin
// A reading of 1 for the A/D = 0.00488mV
// if we multiply the A/D reading by 0.00488 then
// we get the voltage on the pin.

batteryVoltage = pinVoltage * Ratio; // Use the Ratio calculated for the voltage divider
// to calculate the battery voltage, Ratio = Vin / Vout

More details at http://arduinotronics.blogspot.com/2012/04/voltage-monitor.html

UPDATE:

Improved voltage reading circuit and sketch at AC Volt Meter 
<10k 30k.="" a="" calculates="" get="" likely="" of="" p="" pair="" r1="" resistors="" this="" till="" you="">(works with DC as well). Rock solid voltage measurement, and very accurate.

The next step is to track the current being consumed by a load, or produced by a 

source. We are using a ACS715 Hall Effect sensor to track the current being passed.

Update! ACS714 Bidirectional current sensor now being deployed. 
This will enable a battery "gas gauge" for "AH IN - AH OUT = AMP Remaining" type monitoring.

http://www.hacktronics.com/Sensors/Current-Sensor-30-to-30-Amp/flypage.tpl.html

Update! ACS712 5amp sensor project at 
http://arduinotronics.blogspot.com/2014/01/volt-amp-watt-hour-meter-shield.html

// read the analog in value:
  sensorValue = analogRead(analogInPin);           
  // convert to milli amps
  outputValue = (((long)sensorValue * 5000 / 1024) - 500 ) * 1000 / 133;
amps = (float) outputValue / 1000;

More details at 

http://arduinotronics.blogspot.com/2012/04/monitoring-power-consumption-with.html

To calculate watt (volts * amps), amp hours (amps * hours), and watt hours (watts * hours) requires tracking the time component, and performing a bit of math:

float watts = amps * batteryVoltage;
sample = sample + 1;
msec = millis();
time = (float) msec / 1000.0;
totalCharge = totalCharge + amps;
averageAmps = totalCharge / sample;
ampSeconds = averageAmps*time;
ampHours = ampSeconds/3600;
wattHours = batteryVoltage * ampHours;

Step 4: Serial Output

Picture of Serial Output

We can now output the results of the calculations to the serial port using the following code:


Serial.print("Volts = " );
Serial.print(batteryVoltage);
Serial.print("\t Current (amps) = ");
Serial.print(amps);
Serial.print("\t Power (Watts) = ");
Serial.print(watts);

Serial.print("\t Time (hours) = ");
Serial.print(time/3600);

Serial.print("\t Amp Hours (ah) = ");
Serial.print(ampHours);
Serial.print("\t Watt Hours (wh) = ");
Serial.println(wattHours);

Step 5: LCD Display

Keeping a computer connected all the time is inconvenient, so I added
a 4 line lcd display to the project.

lcd.setCursor(0,0);
lcd.print(batteryVoltage);
lcd.print(" V ");
lcd.print(amps);
lcd.print(" A ");

lcd.setCursor(0,1);
lcd.print(watts);
lcd.print(" W ");
lcd.print(time/3600);
lcd.print(" H ");

lcd.setCursor(0,2);
lcd.print(ampHours);
lcd.print(" Ah ");
lcd.print(wattHours);
lcd.print(" Wh ");

Step 6: Source Code

#include

/* This sketch describes how to connect a ACS715 Current Sense Carrier
(http://www.pololu.com/catalog/product/1186) to the Arduino,
and read current flowing through the sensor.

*/

LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

/*

Vcc on carrier board to Arduino +5v
GND on carrier board to Arduino GND
OUT on carrier board to Arduino A0



Insert the power lugs into the loads positive lead circuit,
arrow on carrier board points to load, other lug connects to
power supply positive

Voltage Divider

9k Ohm from + to A4
3k Ohm from A4 to Gnd

*/

int Vin = 20;

int Vout = 5;

int ratio = Vin / Vout; // Calculated from Vin / Vout

int batMonPin = A4; // input pin for the voltage divider
int ADCVal = 0; // variable for the A/D value
float pinVoltage = 0; // variable to hold the calculated voltage
float batteryVoltage = 0;

int analogInPin = A0; // Analog input pin that the carrier board OUT is connected to
int sensorValue = 0; // value read from the carrier board
int outputValue = 0; // output in milliamps
unsigned long msec = 0;
float time = 0.0;
int sample = 0;
float totalCharge = 0.0;
float averageAmps = 0.0;
float ampSeconds = 0.0;
float ampHours = 0.0;
float wattHours = 0.0;
float amps = 0.0;

int R1 = 9000; // Resistance of R1 in ohms
int R2 = 3000; // Resistance of R2 in ohms

int ratio = 0; // Calculated from Vin / Vout

void setup() {
// initialize serial communications at 9600 bps:
Serial.begin(9600);
lcd.begin(20, 4);
}

void loop() {

int sampleADCVal = 0;
int avgADCVal = 0;
int sampleAmpVal = 0;
int avgSAV = 0;

for (int x = 0; x < 10; x++){ // run through loop 10x

// read the analog in value:
sensorValue = analogRead(analogInPin);
sampleAmpVal = sampleAmpVal + sensorValue; // add samples together

ADCVal = analogRead(batMonPin); // read the voltage on the divider
sampleADCVal = sampleADCVal + ADCVal; // add samples together

delay (10); // let ADC settle before next sample

}

avgSAV = sampleAmpVal / 10;

// convert to milli amps
outputValue = (((long)avgSAV * 5000 / 1024) - 500 ) * 1000 / 133;

/* sensor outputs about 100 at rest.
Analog read produces a value of 0-1023, equating to 0v to 5v.
"((long)sensorValue * 5000 / 1024)" is the voltage on the sensor's output in millivolts.
There's a 500mv offset to subtract.
The unit produces 133mv per amp of current, so
divide by 0.133 to convert mv to ma

*/


avgADCVal = sampleADCVal / 10; //divide by 10 (number of samples) to get a steady reading

pinVoltage = avgBVal * .00488; // Calculate the voltage on the A/D pin
/* A reading of 1 for the A/D = 0.0048mV
if we multiply the A/D reading by 0.00488 then
we get the voltage on the pin.



Also, depending on wiring and
where voltage is being read, under
heavy loads voltage displayed can be
well under voltage at supply. monitor
at load or supply and decide.
*/


batteryVoltage = pinVoltage * ratio; // Use the ratio calculated for the voltage divider
// to calculate the battery voltage


amps = (float) outputValue / 1000;
float watts = amps * batteryVoltage;

Serial.print("Volts = " );
Serial.print(batteryVoltage);
Serial.print("\t Current (amps) = ");
Serial.print(amps);
Serial.print("\t Power (Watts) = ");
Serial.print(watts);


sample = sample + 1;

msec = millis();



time = (float) msec / 1000.0;

totalCharge = totalCharge + amps;

averageAmps = totalCharge / sample;

ampSeconds = averageAmps*time;

ampHours = ampSeconds/3600;

wattHours = batteryVoltage * ampHours;





Serial.print("\t Time (hours) = ");
Serial.print(time/3600);

Serial.print("\t Amp Hours (ah) = ");
Serial.print(ampHours);
Serial.print("\t Watt Hours (wh) = ");
Serial.println(wattHours);


lcd.setCursor(0,0);
lcd.print(batteryVoltage);
lcd.print(" V ");
lcd.print(amps);
lcd.print(" A ");

lcd.setCursor(0,1);
lcd.print(watts);
lcd.print(" W ");
lcd.print(time/3600);
lcd.print(" H ");

lcd.setCursor(0,2);
lcd.print(ampHours);
lcd.print(" Ah ");
lcd.print(wattHours);
lcd.print(" Wh ");

lcd.setCursor(0,3);
lcd.print(ratio, 5);
lcd.print(" ");
lcd.print(avgBVal);

// wait 10 milliseconds before the next loop
// for the analog-to-digital converter to settle
// after the last reading:
delay(10);
}

Attachments

• wattmeter.xls
  Download
• watt_meter_lcd.ino
  Download

Step 7: Future Expansion

The hybrid relay enables spinoffs like dump load controllers for wind turbines, and load shedding for multi stage power downs or controlled power usage based on battery voltage or load priority.

Step 8: Protoboard

We have moved the current and voltage sensor off the solderless breadboard,
and onto a Radio Shack proto board. This is more sturdy and "permanent"