10. Output Devices

Group assignment:

• Measure the power consumption of an output device.

• Document your work on the group work page and reflect on your individual page what you learned.

Measuring instruments

We used several measuring instruments as part of our group assignment.

Power Supply

A power supply is a universal tool for generating direct current (DC), setting current limits and thresholds, and measuring power consumption in projects requiring up to 30V and 3A. We use the Instek GPD-3303D power supply, which features:

• Two adjustable channels (0-30V, up to 3A each).

• One fixed channel (2.5V / 3.3V / 5V, up to 3A).

On the back panel, the input voltage options are available. We use 220V, which is the standard voltage in our country.

We will measure the power consumption of several DC motors and an LED strip. To connect a DC motor to the power supply, polarity does not matter, as it only affects the rotation direction.

Multimeter

When working with a multimeter, there are two wiring configurations:

1. Voltage or resistance measurement – probes must be connected in parallel to the circuit.

2. Current measurement – the multimeter must be placed in series with the circuit.

The black probe (-) is always connected to the COM port. The red probe is connected to different ports depending on the type of measurement.

LED strip consumption

We connected the LED strip with a nominal voltage of 12 V to the Instek GPD-3303D laboratory power supply and changed the voltage from 1 V to 13 V.

The LED strip began to glow at 6 V, but the glow was dim. At 13 V, the brightness was higher than at 12 V, which confirms the dependence of the glow intensity on voltage.

Measurement results

Voltage (V)	Current (A)	Power (W)	Energy Consumption (Wh)
1.0V	0.00A	0.00W	0.00Wh
6.0V	0.07A	0.42W	0.42Wh
9.0V	0.62A	5.58W	5.58Wh
12.0V	1.22A	14.64W	14.64Wh
13.0V	1.43A	18.59W	18.59Wh

Current measurement

To compare the readings, we connected an ammeter in series with the LED strip and compared its readings with the measurements of the power supply.

The reading of the Instek GPD-3303D power supply is 1.22 amps, and the multimeter reading was 1.23 amps.

DC Motor Power Consumption

Introduction

The goal of this experiment is to measure the power consumption of an output device using various measurement tools. We record voltage, current, power, and calculate energy consumption over a certain period.

Measurement Method

Measurement Parameters:

• Voltage (V) – measured in volts (V).
• Current (A) – measured in amperes (A).
• Power (W) = Voltage × Current.
• Energy Consumption (Wh) = Power × Operating Time.

Equipment:

• Instek GPD-3303D power supply - for power supply and current measurement

Measurement Process

Power Consumption of a 12V Motor

1. Supply 12V from the laboratory power supply.

2. Record measurements in different modes:

Free rotation:

• Voltage: 12.0V

• Current: 0.06A

• Power: 12.0V × 0.06A = 0.72W

Increased load (by applying pressure with a finger):

• Voltage: 12.0V

• Current: 0.59A

• Power: 12.0V × 0.59A = 7.08W

Complete motor stop:

• Voltage: 12.0V

• Current: 1.46A

• Power: 12.0V × 1.46A = 17.52W

1. Measure energy consumption over 1 hour in different modes:

   • Free rotation: 0.72 Wh

   • Under load: 7.08 Wh

   • When stopped: 17.52 Wh

Measurement Results

Motor Operating Mode	Voltage (V)	Current (A)	Power (W)	Energy Consumption (Wh)
Free rotation	12.0V	0.06A	0.72W	0.72Wh
Partial load	12.0V	0.59A	7.08W	7.08Wh
Complete stop	12.0V	1.46A	17.52W	17.52Wh

Conclusions

• As the load increases, the current also increases, leading to higher power consumption.

• Maximum consumption occurs when the motor is completely stopped.

• Using precise measurement instruments allows for objective data collection.

Motor Startup Process

Introduction

In this experiment, we investigate the behavior of DC motor power consumption during startup and control via MOSFET using pulse width modulation (PWM).

Experiment

Connecting the Motor to GPD-3303D

Connect the DC motor to the Instek GPD-3303D lab power supply with 12 V.

We observe that the current consumption increases significantly during startup.

After the motor adaptation, the power consumption decreases and stabilizes at the operating level.

Motor Control via MOSFET

Connect the DC motor via a MOSFET transistor, which is controlled by the control board.

Control the motor speed using pulse width modulation (PWM).

const int pwmPin = 3; // PWM pin for MOSFET control
const int runPWM = 36; // Working PWM (0-255)

void setup() {
    pinMode(pwmPin, OUTPUT);
}

void loop() {
    // Start with PWM
    analogWrite(pwmPin, startPWM);
}

We find that at low PWM values, the motor does not start without external influence (for example, a push).

To solve this problem, we implement a software artificial starter:

At the start, we apply a high PWM signal to start the motor.

After reaching the initial rotation, we reduce the PWM to save energy and maintain stable operation.

const int pwmPin = 3; // PWM pin for MOSFET control
const int startPWM = 50; // High PWM at start (0-255)
const int runPWM = 36; // Working PWM after start (0-255)
const int startTime = 500; // High PWM time (ms)

void setup() {
    pinMode(pwmPin, OUTPUT);
}

void loop() {
    // Start with high PWM
    analogWrite(pwmPin, startPWM);
    delay(startTime);

    // Switch to working PWM
    analogWrite(pwmPin, runPWM);

    // Further operation or control by conditions
}

As a result, we get the following result:

Conclusions

The motor power consumption is significantly higher at the moment of start-up than in stationary mode.

When controlled via a MOSFET at low PWM values, the motor may not start without assistance.

A software artificial starter can eliminate this problem, providing a smooth start for the motor.

This method can be useful when working with motors in power-constrained systems, such as battery-powered devices and robotics projects.

ACS712 Current Sensor

Necessary components

• ACS712 module (5A, 20A or 30A)

• Arduino Uno

• DC motor (e.g. 12V)

• Power supply (battery or 12V adapter)

• Connecting wires

Connection

Power section (current measurement)

ACS712 is connected in series with the motor circuit:

• IN+ of the ACS712 module → Positive of the motor power supply (12V).

• IN- of the ACS712 module → Positive of the motor input (or motor driver).

• GND (motor power) remains common.

Signal part (Arduino)

• VCC (ACS712) → 5V (Arduino Uno)

• GND (ACS712) → GND (Arduino Uno)

• OUT (ACS712) → A0 (Arduino analog input)

Experiment code

This code will measure the current and print it to the Serial Monitor.

int analogPin = A0; // Specify the OUT port of the ACS712 sensor

const int averageValue = 500; // Variable for storing the number of reading cycles
long int sensorValue = 0; // Variable for storing the value from the sensor

float voltage = 0; // Variable for storing the voltage value
float current = 0; // Variable for storing the current value

void setup() {
    Serial.begin(9600); // Open serial communication at 9600 speed
}

void loop() {
    for (int i = 0; i < averageValue; i++) { // Repeat the loop
        sensorValue += analogRead(analogPin); // Read and write readings
        delay(2); // Pause for 2 μs
    }

    sensorValue = sensorValue / averageValue; // Divide the resulting value
    voltage = sensorValue * 5.0 / 1024.0; // Calculate voltage
    current = (voltage - 2.5) / 0.185; // Calculate current

    Serial.print(" Current: "); // Send data to serial port
    Serial.print(current); // Send current
    Serial.println("A"); // Send data to serial port
}

Conducting the experiment

• Run the code and open the Serial Monitor in the Arduino IDE.

• Without load (motor off) the current reading should be around 0A (±0.1A).

• Turn on the motor - the current should increase.

• Load the motor (for example, press the shaft) - the current will increase.

Additional points

• If the motor runs in both directions, the current can be both positive and negative.

• If the signal jumps, add a 100 nF capacitor between OUT and GND.

• For smooth measurements, you can average several values.

• The ACS712 is sensitive to external magnetic fields from permanent magnets and high-current wires, which can affect the accuracy of measurements.

Conclusions

The ACS712 can be used in projects to monitor current consumption, protect against overloads, and diagnose motor operation. However, it is necessary to take into account its sensitivity to external magnetic fields, which can affect the accuracy of measurements.

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Last update: March 30, 2025