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Thread: DISPLAY_ILI9341_TOUCH power consumption

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    DISPLAY_ILI9341_TOUCH power consumption

    I ordered a DISPLAY_ILI9341_TOUCH and I want to power it from 5V. I am designing a power circuit and wanted to know, what is the power consumption for this device?

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    Quote Originally Posted by geekEE View Post
    I ordered a DISPLAY_ILI9341_TOUCH and I want to power it from 5V. I am designing a power circuit and wanted to know, what is the power consumption for this device?
    You would first have to decide how bright you want the backlight as that uses much of the required current. Also how you are updating the display, constant updates are likely to affect this. The LED input on the board is fed via a current limit resistor, either directly from Vsupply or from a micro output pin, with the later arrangement you can control backlight on/off and can PWM the supply to set brightness.

    Steve

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    Quote Originally Posted by geekEE View Post
    I ordered a DISPLAY_ILI9341_TOUCH and I want to power it from 5V. I am designing a power circuit and wanted to know, what is the power consumption for this device?
    Funny you should ask! A few days ago, I had a setup to measure power consumption of the T4.1 while writing to the SD Card. The setup uses a high-side current sensor on the T4.1 power input and measures the current at 16,000 samples per second. I connected the setup to my T4.1 with the ILI9341 display and recorded the power consumption while reading in a QVGA image from SD, then dissolving in a second image.

    The ILI9341 backlight is fed the input 5V through a 100-ohm current limiting resistor. The baseline current of the T4.1 is about 125mA at 600MHz. With the ILI9341 displaying a static image, the current rises to about 165mA. The extra 40mA seems consistent with the resistor value and about a 1V drop across the backlight LED.

    Strangely, the overall current drops when the PXP is actively managing a 30-step dissolve into a new slide. There are some expected current spikes to about 230 to 240mA when the new files are being read from the SD card.

    Here is a plot of the current data vs time:
    Click image for larger version. 

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    A file has already been read and is being displayed at T=0. At about T=17, file 1 is read and displayed. At T=26, a file 2 is read and dissolves in over file 1. The drop in current during the transition is apparent and unexplained.

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    The drop in current suggests the processor is halting and waiting for interrupt. Bulk SPI
    operations are probably being DMA'd.

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    Quote Originally Posted by MarkT View Post
    The drop in current suggests the processor is halting and waiting for interrupt. Bulk SPI
    operations are probably being DMA'd.
    That was my thought too. A closer examination of the timing of the low-current part shows that those periods last about the same interval as the timing info shows for an average update of the ILI9341 (about 41mSec). I looked at the code in the ILI9341_t3n.cp and the SPI.CPP sources, but didn't find any explicit __WFI instructions, but there might be other ways in which the power could be reduced during the DMA-based screen updates.

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    My other thought was a busy-waiting loop would be entirely in cache and avoid hitting RAM for instruction fetch or any load/stores.

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