From 59629dd38c17d3785e9fe08c55853c1fa0bfbbb6 Mon Sep 17 00:00:00 2001 From: Peter Hinch Date: Tue, 26 Jan 2021 13:11:31 +0000 Subject: [PATCH] DRIVERS.md add EPD micopower measurements. --- DRIVERS.md | 29 +++++++++++++++++++++++++---- 1 file changed, 25 insertions(+), 4 deletions(-) diff --git a/DRIVERS.md b/DRIVERS.md index 1f938be..bbe8489 100644 --- a/DRIVERS.md +++ b/DRIVERS.md @@ -705,10 +705,31 @@ Users of other EPD's may want to develop other means of powering down the EPD. A p-channel MOSFET could be considered as described [here](https://github.com/peterhinch/micropython-micropower/blob/master/HARDWARE.md#hardware-issues). -In use I measured 500μA in the periods when the display is refreshing (a total -of 10s for each wakeup) and 58μA between wakeups. The Pyboard accounts for -about 6μA. 33μA will be used by the 100KΩ pullup on the breakout's power enable -line. I haven't attempted to figure out where the other 19μA is going. +##### Measurements + +In use I measured 58μA between wakeups. The Pyboard accounts for about 6μA. +33μA will be used by the 100KΩ pullup on the breakout's power enable line. I +haven't attempted to figure out where the other 19μA is going. + +I measured power consumption for a hypothetical application which wakes once +per hour, refreshes the screen, and goes back to sleep. In summary it uses +0.74AH per year. This suggests it could run for ~3 years on a set of alkaline +AA cells (capacity 2.5AH). + +Of the total, the 58μA sleep current accounts for 0.5AH, and the wakeup current +0.24AH. Of the wakeup current, 28% is used for physical display refresh and a +further 39% during SPI transfer to the display. The remaining 33% is used by +boot (3%), initialisation of the device (2.8%), and initialisation of nano-gui +(27%). This is based on study of the current waveform in conjunction with +guessing what is going on in each phase of operation. + +The measurements used frozen bytecode on a Pyboard D SF6W. No SD card was +fitted. Code was `epd29_lowpower.py` with the red LED code removed. + +The fact that nearly 70% of the energy is used in standby suggests +improvements. If the EPD subsystem were turned off by a p-channel MOSFET, +current consumption could be reduced to the 6μA figure of the Pyboard, an order +of magnitude improvement. ###### [Contents](./DRIVERS.md#contents)