Week 10 Output devices
This page documents the group assignment for week 10 of Högni, Jóhannes and Ólöf.
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.
Overview and approach
We did the group assignments in two different locations.
Högni and Jóhannes worked at Fab Lab Ísafjörður and documented about it.
Ólöf worked at Fab Lab Austurland and documented about it.
Theory
Voltage, current and power
Electrical power is the product of voltage and current.
We can easily measure the voltage we supply to a device with a multimeter.
The most common approach to measure DC current is by placing a resistor that can handle high current and has a low resistance in the circuit and measuring the voltage drop over this resistor (shunt resistor). Then Ohm's law can be used to calculate the current.
That is what a multimeter does, when connecting the lead to the A input.
Warning
It is advised to check the maximum allowed current and measuring duration to not overload the multimeter. A typical multimeter has two different inputs - one with 600 mA fuse and one with 10 A fuse.
Settings on the Multimeter
Settings on the Multimeter
The Multimeter is set to measure Direct Current (DC) and you can see the symbol for it at the top left on the screen. Then the probe has to be inserted in the right place. The probe goes into the connector for measuring milliamps (mA). The connector that is used in this image can handle up to 0,5 Ampers, so if you are going to measure something with more current you should use the other connector that is marked with 10 A.
Fab Lab Ísafjörður
Jóhannes measured the power consumption of the 0,96'' OLED display (128 x 64 px) and the unipolar stepper motor 2138812.
The OLED display uses an average of 4,86 mA. With a supply voltage of 3,3 V, that means an average power consumption of 16 mW.
The stepper motor (including the driver) has a holding current of 359 mA.
When running, the average current flow drops, with increasing speed. (ranging from 247 mA to 361 mA)
Load seems to have no impact on the power consumption of this motor.
With a supply voltage of 5 V, that means an average power consumption of 1,8 W.
Fab Lab Austurland
Measuring power consumption
The power consumption of a Liquid Chrystal Display
Ólöf measured the power consumption of a Liquid Chrystal Display (LCD) with a Multimeter. The Multimeter was set for measuring Direct Current (DC) and the probe was in the slot for measuring milliamps (mA). This image shows where the probes were placed to measure the current.
Calculating the power
The power consumption of a Liquid Chrystal Display
The power consumption was around 24,20 mA. To calculate the power I used the formula:
V (Voltage) x I (Amper) = P (Power). 5V x 24,2 mA = 121 mW
