10. Output Devices

This week’s group assignment was to measure the Power Consumption of output devices.

To determine the power consumption and select a suitable power source, we first need to find the Power consumption (in Watts) (or amperage) of one device, by multiplying Voltage (Volts) x Current (Amps). Then, we need to calculate the total Wattage by multiplying the wattage per unit x the number of units.
Finally, we choose a power supply that can provide at least the calculated wattage, with a 20% buffer for safety and longevity.

1. Power consumption of LEDs

An average LED bulb typically consumes between 5 ~ 20 watts, depending on its brightness and type.
According to the datasheet, the power consumption of our LED is xxxx.
We used the multimeter to measure the voltage (V) and current (mA) of an LED.

Procedure

Tools used:
- Power source: 5V
- LEDs
→We need links for LED datasheet
→such as, What is its Voltage drop / forward Voltage (Vf) (the amount voltage needed before any current can flow across it.)
→What is its Forward Current (If) (the maximum current it can handle?)
- Resistors (330 Ω)
- Multimeter

Measuring method:
Voltage: Clamp both ends of the thing you want to measure with the multimeter
LED voltage: Connect the + of the multimeter to the + pin of the LED, and the - of the multimeter to the - of the LED, and measure
Resistor voltage: Measure by clamping a multimeter to each pin of the resistor
Current: Clamp a multimeter between the circuit
(If clamping between the Arduino and the LED, connect the + of the multimeter to the Arduino signal line, and the - of the multimeter to the + of the LED)

Measured circuit:
Each resistors were connected to the LED as below:
(1) 1 resistor
(2) 2 resistors connected in series
(3) 2 resistors connected in parallel

• Since the current is small, the voltage does not change even if the current changes.
  

  The voltage drop across an LED is not truly constant but rather has a forward voltage characteristic.
  While the voltage may not change significantly with minor current variations, it does not remain perfectly constant as current increases. This voltage drop, called the forward voltage (Vf), is a key characteristic of an LED. - Link
  

Theoretical Values

Number of resistors	Current of the entire circuit	Resistor value	Voltage of LED	Resistor voltage	voltage All	Power Consumption
(1) 1 resistor	0.01A	330Ω	2V	3V	5V	0.005 Watts
(2) 2 resistors (series)	0.005A	660Ω	2V	3V	5V	0.025 Watts
(3) 2 resistors (parallel)	0.018A	165Ω	2V	3V	5V	0.09 Watts

Results

Number of resistors	Current of entire circuit	Resistor Value	LED voltage	Resistor voltage	voltage All	Power Consumption
(1) 1 resistor	0.0082A	330Ω	1.9V	2.7V	4.7V	0.0042 Watts
(2) 2 resistors (series)	0.0046A	660Ω	1.9V	R1:1.5V R2:1.5V	4.9V	0.0225 Watts
(3) 2 resistors (parallel)	0.015A	165Ω	2.0V	R1:2.4V R2:2.4V	4.6V	0.0695 Watts

It was confirmed that there was no significant deviation from the theoretical values.

1 resistor	2 resistors (series)	2 resistors (parallel)

2. Power Consumption of Stepper motors

We checked how the current varies depending on the voltage and the number of Stepping Motors.

Measuring procedure

Equipments:
- A regulated power supply: Can output a constant voltage. With a regulated power supply in FLK, the following can flow:
→ Voltage: Adjustable between 0-20 V
→ Current: Also adjustable (without needing resistors) between 0-5 A
- DRV8825 Motor Driver ([Tutorial(https://lastminuteengineers.com/drv8825-stepper-motor-driver-arduino-tutorial/)])
→ Motor output voltage: 8.2V – 45V
→ Logic voltage: Built-in 3.3V output
→ Continuous current per phase: 1A
→ Maximum current per phase: 2.5A
→ Microstep resolution: full, 1/2, 1/4, 1/8, 1/16, and 1/32
- CNC Shield, to attach Arduino to Driver (100μF Capacitor)
- Vmot - モーター駆動用の電源電圧
- 1st Stepper motor: Bi-Polar 42HD4027-01-A Torque 0.4N·m)
- 2nd Stepper motor: Bi-Polar ST-428YH1684

A stepping motor is a brushless DC electric motor that moves in discrete steps, allowing for precise angular position control without feedback mechanism. These motors are characterized by their ability to rotate in small, defined steps in response to digital pulses, enabling accurate positioning and speed control.

Stepper motor torque is directly proportional to the current flowing through its windings.
Higher voltage generally leads to higher current, and therefore, higher torque, up to a saturation point where the motor’s magnetic properties limit further increase in torque. However, the ability to maintain sufficient torque at higher speeds is also influenced by the voltage. - Source

Our Stepper motor	Description	42HD4027-01-A	ST-428YH1684
Rated Voltage	The maximum voltage the motor is designed to operate at	3.3V DC	5.0V
Rated current	The maximum current the motor is designed to operate at	1.5A	1.0A
Rated Power Consumption	Voltage x Current	4.95 Watts	5.0 Watts

Theoretical Values

Since resistance value (i.e., of motor device) does not change;
- When voltage is decreased: Current should increase
- When voltage is increased: Current should decrease
(If the voltage = power increases, the current = amount decreases, and if the voltage = power decreases, the current = amount increases, to keep the motor moving in a constant manner according to the signal from the microcontroller)
- When the number of motors increases: the current should increase, to supply sufficient power to the motor.

Results

Current at driving voltage of:	9V	12V	16V	19V
1 motor	0.14A	0.11A	0.09A	-
Power Consumption for 1 motor	1.26 W	1.32 W	1.44 W	-
2 motors	0.29A	0.23A	0.19A	0.16A
Power Consumption for 2 motors	2.61 W	2.76 W	3.04 W	3.04 W

9V	12V	16V	19V

The following was confirmed
- As voltage decreases, current increases
- As the number of motor increases, the current increases
- Power consumption stays

Useful links

• Try lecture video