Week 13: Output Devices
Tasks
- Measure the power consumption of an output device
For this week we will be measuring the power consumption of this OLED screen. Both students in this lab work at Core Electronics and we thought that we would get some power consumption readings for a device we manufacture here. This is an SSD1306-based OLED that is a part of our PiicoDev I2C system.
To test the power consumption we fired up the Otii Arc Pro which is a voltage supply that measures power consumption with incredible accuracy - being able to measure down to the 100s of nano Amps.
To test it we plugged it into a Pico via I2C, supplied it with the Otii Arc's power at 3.3 Volts, and ensured that it shared a common ground with the Pico.
Then we booted up the Otii Arc Software, turned on the power supply and hit record while running a test script for the OLED screen (which you can find at the bottom of the page as well as the dependant libraries). This is what we saw and we tried to get the oled screen in shot as well so that you can see what the OLED shows vs the power consumption.
And this was our resulting graph, the first "chunk" was junk from the last test, after that it moves into displaying a few numbers on screen, then the bar graphs are responsible for that climbing slope, at the peak we then cut to some sine waves being drawn, and then we fill the screen fully white, and then turn everything off, And that final chunk is the bouncing box animation.
An interesting note is that the current being drawn fluctuates rapidly, here is a close up of one of those sections.
But thankfully the Otii Arc is able to measure the area under the plot and give us power consumption. Here are our findings from 2 second samples:
Results
Max Power Draw (all pixels white): 85.8 mW @ 26 mA
Min Power Draw (all pixels black): 3.74 mW @ 1.13 mA
Power draw with some text: 13.2 - 33 mW @ 4 - 10 mA
Idle Power Draw (Device not intialised): 0.333 mW @ 0.101 mA