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What is it

This is a collection of:

  • sleepy pi 2 replacement arduino scripts that allow for setting the sleep/wake timers from the rpi, and for reading the current/voltage from the rpi
  • a daemon written in python to be ran on the rpi, that allows to see values and set sleep/wake regime from a MQTT app (eg android MQTT dash), and a free MQTT broker (eg dioty)
  • small programs to update retained values on the MQTT broker. this way, we can update the sleep/wake regime remotely.

features of the arduino part

  • pi status tracker that implements a raspberry pi state machine (eg booting, running, halting, ...) without blocking/sleep calls on the arduino so that it interoperates with other software running on the arduino.

  • holding the power button on the arduino will initiate a reboot of the rpi (with a 20sec pause between the power off and power on, allowing for safe power cut)

  • watchdog (the built-in raspberry pi watchdog gets confused on brown-out)

  • following I2C registers are available (address 0x36):

    • REG_SIGNATURE = 0 : byte, fixed signature (for easy detection of the arduino), should be 58
    • REG_VOLTAGE = 1 : float32 little endian, supply voltage measured by the sleepy pi
    • REG_CURRENT = 5 : float32 little endian, current measured by the sleepy pi
    • REG_THRESH_SUSPEND_VOLT = 9 : float32 little endian, if the voltage drops below the value, it will suspend
    • REG_THRESH_RESUME_VOLT = 13 : float32 little endian, if voltage goes above voltage, it will get out of suspend
    • REG_ALARM_HOUR = 17 : alarm timer hour (watch out time zone!)
    • REG_ALARM_MINUTE = 19 : alarm timer minute
    • REG_SECONDS = 21 : alarm timeout seconds (either use the alarm, either use the seconds timer)
    • REG_COMMAND = 25 : command register. updating this register initiates an action:
    • REG_WATCHDOG = 26 : the watchdog counter. byte. set at 60 at boot, ticks down until it reaches 1, then triggers reboot cycle

  • the following commands are available:

    • CMD_NOTHING=0 : no command
    • CMD_WAIT_ALARM=1 : shutdown the raspberry pi, set RTC alarm and wait for RTC alarm, then restart the raspberry pi
    • CMD_WAIT_TIMER=2 : same as WAIT_ALARM, but now wait a fixed number of seconds. due to the fact that we only have 16 bits on the RTC, this can be inaccurate!
    • CMD_POWEROFF_EXT=4 : disable external power (untested)
    • CMD_POWERON_EXT=5 : enable external power (untested)

features of the python daemon

  • tries to find network connection. when it has no network connection after 200 secs, it assumes connecting went wrong (eg due to unreliable 3G) and initiates a reboot using the sleepy pi.
  • exposes all measurements of the sleepy pi through mqtt retained values
  • allows taking a photo by publishing mqtt /[root]/takephoto to 1 (photo will be published to another mqtt topic)
  • has a simple sleep/wake scheduler (now 2 behaviours are implemented: always on and cyclic)

How to get it running:

  • follow the official sleepypi 2 instructions to set up the sleepy pi environment on your rpi

  • using the arduino IDE (better use the version recommended by the sleepy pi 2 docs, not necessarily the latest version), upload the sketch. If uploading to arduino fails, make sure to check if your getty on ttyS0 is not running anymore.

    check sudo systemctl stop [email protected] --> should not be running

  • reduce the baudrate of i2c (arduino is not fast enough and raspberry pi does not allow clock stretching): Add the following line to /boot/config.txt:

    dtparam=i2c_baudrate=50000

  • create a "run forever" script for the offgridpi_daemon python starting it up with the right credentials

tweaks increasing reliability

rpi watchdog