Week 10: Output Devices

Group Assignment

In this assignment, we analyzed the power consumption of different output devices by measuring their current and voltage during operation.

Power in an electrical system is the rate at which energy is transferred or used. It is measured in watts (W) and calculated using the equation:

\( P = V \times I \)

Where:

• P = Power in watts (W)
• V = Voltage in volts (V)
• I = Current in amperes (A)

This equation tells us that the power consumed by a device depends on both the voltage applied to it and the current it draws.

Voltage is the potential difference between two points in a circuit, measured in volts (V). It represents the "electrical pressure" that pushes electrons through a conductor. A higher voltage means a stronger push for electrons, which can drive more current through a circuit.

Current is the flow of electric charge through a conductor, measured in amperes (A). It depends on the voltage applied and the resistance of the circuit.

By using Ohm’s Law, we can calculate the current:

\( I = \frac{V}{R} \)

Where:

• I = current (A)
• V = voltage drop across the shunt (V)
• R = known resistance of the shunt (Ω)

To measure the current, we used the display of our power supply and three types of measuring devices: a USB tester, multimeters, and a clamp meter.

The USB tester measures voltage and current flowing through the USB power line and displays the real-time power consumption of the connected device.

The tester has a low-resistance shunt resistor (typically 0.01Ω to 0.05Ω) inside. When current flows through this resistor, a small voltage drop is created, and by using Ohm’s Law, the device calculates the current.

The digital multimeter measures current by acting as an ammeter when set to the appropriate mode. To measure the current, we connected the multimeter to the circuit in series.

Just like the USB tester, when current flows through the multimeter, a shunt resistor drops a tiny voltage. The DMM reads this voltage drop and, using Ohm’s Law, calculates the current.

Finally, we used a clamp ammeter, which works on the principle of electromagnetic induction.

The clamp meter does not need direct contact with the wire; it senses the magnetic field generated by the flowing current. The meter then converts this field strength into an equivalent current reading.

This device is more well suited for high power devices, such as large motors or heating elements.

TEST 1 - DC6V GBMQ-GM12BY20 Geared Motor

For the first test, we measured a DC6V GBMQ-GM12BY20 Geared Motor with Magnetic Disc Hall Encoder (6V 70 RPM).

We connected our power supply to a custom PCB fitted with a 5V regulator to control and feed the motor. We connected the microcontroller to our USB tester and the tester to our computer.

The largest current measured was 0.160A, with a voltage of 5V, so our max power consumption was:

\( P = 5V \times 0.160A = 0.8W \)

TEST 2 – DS3218 High-Torque 20kg-cm Digital Servo Motor

For the second test we measured a DS3218 servo motor with no load attached.

We connected the servo to a custom PCB and set our external power supply to 6V and 2A max.

When idle, the motor consumes 0.008A, meaning that:

\( P_{idle} = 6V \times 0.008A = 0.048W \)

When moving, the motor consumed a maximum of 0.555A, meaning that:

\( P_{max} = 6V \times 0.555A = 3.33W \)

TEST 3 – NEMA 17 HS08-1004S

The third test involved a Nema 17 stepper motor with no load attached.

We connected the motor to an A4988 driver on our custom PCB, and set the external power supply to 12V and 1A max.

When idle, the motor consumes 0.14A, meaning that:

\( P_{idle} = 12V \times 0.14A = 1.68W \)

When moving, the motor consumed a maximum of 0.18A, meaning that:

\( P_{imax} = 12V \times 0.18A = 2.16W \)

TEST 4 – TowerPro MG995 High-Speed Metal Gear Servo

The fourth test involved an MG995 servo motor with no load attached.

We connected the motor to the PCB and set our external power supply to 6V and 1A max.

The initial current was fluctuating around 0.067A, this may be due to an initial calibration, the resulting power consumption is:

\( P_{initial} = 6V \times 0.067A = 0.402W \)

When moving, our power supply registered a max current of 0.330A for an instant, while the multimeter registered a maximum of 0.280A. For the calculations, we’ll take the maximum registered by the power supply:

\( P_{max} = 6V \times 0.330A = 1.98W \)

Once stabilized, the idle current was 0.007A, meaning that:

\( P_{idle} = 6V \times 0.007A = 0.042W \)

TEST 5 – Heating Jacket

Our fifth test involved a much more powerful device, a heating jacket, which is an electrically powered device designed to evenly heat objects to precise temperatures.

The device is controlled through a digital thermostat and a relay. The thermostat allows us to set the desired temperature and turns the relay on and off to maintain said temperature.

For this test we used the clamp meter, which measured 3.3A at 120V, so our power consumption was:

\( P = 120V \times 3.3A = 396W \)

TEST 6 - GC9A01A TFT LCD

The sixth test involved two GC9A01A displays. The devices are controlled through SPI and feed directly from the 3.3V output of the microcontroller.

When using a single display, our maximum registered current was 19.87mA (0.01987A), meaning that:

\( P_{single} = 3.3V \times 0.01987A = 0.06557W \)

When using both displays at the same time, we registered a max current of 36.61mA (0.03661A), meaning that:

\( P_{two} = 3.3V \times 0.03661A = 0.12081W \)

TEST 7 – NEOPIXEL

For our final test, we used a high intensity neopixel module connected to a custom PCB.

When at its brightest, the maximum registered current was 0.11A at 5V, making the power consumption:

\( P = 5V \times 0.11A = 0.55W \)