I want to deploy a RPi 3 in quasi-headless mode, i.e. no display attached, with an application running that takes time-lapse photos (with the standard camera module). Power is supplied through a battery pack, so I want to minimise energy consumption.

I have installed regular Raspbian, i.e. with XFCE, and I would like to avoid having to re-install a headless Jessie lite just for this application. (As I might use some javax.imageio API, I'm not even sure that I can technically run in headless)

I read this article, and one thing that seems recommended is to turn off HDMI. I also suppose that not starting the X Server but remaining in text mode might save energy.

So my idea is that I temporarily disable the HDMI output, and I temporarily might also be able to avoid booting into XFCE. I take it that I should connect the Pi via SSH and perform these steps.

Which are the steps necessary to deactivate HDMI and stop before the X Windows login, and which are the steps to revert to previous behaviour ("desktop computer")? Any additional things I should disable (e.g. on-board audio)?

  • Although you can do it if you want, disabling the X server will save you exactly zero energy if it is not actively being used -- which obviously it won't be if you are using the pi headless. In fact, it would not add anything significant even if it were being used (discounting the necessary peripherals); the most significant thing it will do resource wise is occupy some RAM, but using or not using RAM does not save energy (as long as the RAM is powered its energy use is more or less constant). – goldilocks Jul 12 '16 at 15:01
  • @goldilocks ok thanks, so I can leave that bit as is, and just disable HDMI, Wifi, Audio, ... – 0__ Jul 12 '16 at 15:05
  • Also, if by "battery back" you mean a power bank mostly intended for recharging things, watch out for the red PWR led flickering on the 3. I've noticed even with a hefty (20 Ah) power bank cable of 2 A output (I've checked that with an ammeter) and the Pi 3 drawing less than 1/4 of that, it still happens and on a display I get the little rainbow square current warning top right flickering as well... – goldilocks Jul 12 '16 at 15:14
  • ...My guess is that these things don't handle sudden fluctuations in draw well (it isn't the peak amount). Dunno how much it matters as it seemed to work fine, but if you have rebooting problems, etc., and that is happening, there you go. YMMV obviously, good luck. – goldilocks Jul 12 '16 at 15:14
  • @goldilocks Yes, I use a 17 Ah power bank with 2.4A. I noticed occasional rainbows when running multiple things (USB audio interface with mic preamp, writing to SD card, running Jack audio), but still everything remained stable. I haven't tested "just cam capture" yet, but I suspect it will work fine, the only question is how long the power supply will last. – 0__ Jul 12 '16 at 15:45

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