Christmas Tree water level sensor and text alerting

Dry Christmas trees are a major fire hazard. I don’t have to link the videos, but they go up in flames super fast. My wife and I are pretty forgetful sometimes so I wanted to find some way of making sure that our tree didn’t go too long without a drink!

Last year I used some soil moisture sensors (but purchased in a 5-pack on ebay for cheap). I ended up using the digital outputs, suspending it in the water between the bolts on the tree stand, and hooking it up to a raspberry pi. It looked like this:
soil sensor in tree water
Well, it sort of worked.. when the water level dropped enough, it changed signals. The problem is that it wasn’t designed to be in tree-sap infested waters. So eventually it just stopped working entirely.

This year I’d like to do better. So instead of using a soil moisture sensor, I purchased a pack of DP5200 float sensors.

With a little bit of corrugated plastic (thank you election season signs) and hot glue, it was pretty easy to suspend the float at an appropriate level in the christmas tree stand:

With my new dupont connector kit it was a breeze to connect this to my Raspberry Pi.

I’m connecting the sensor to the I2C pin and ground on the Raspberry pi as it already has an internal pull-up resistor and I don’t need to add an external one for the switch.

The code consists of two new files and one modified rc.local for startup. I set up an account on Twilio to send the text messages.

First, the initialization file at /root/tree/ — this simply initializes the GPIO as an input.


echo 3 > /sys/class/gpio/export
echo in >  /sys/class/gpio/gpio3/direction

Second, the actual monitoring code at /root/tree/ — This sends an initial state to the numbers, and then watches the state for a consistent seconds of 0 or 1, and will only send an alert if the state actually changed and was consistent for 15 full seconds. So, in the actual event of a state change from empty to full or full to empty, it will take between 16 and 30 seconds to receive an alert.


function text {
  ## $1 = number
  ## $2 = status.  0=needs water, 1=plenty of water
  [ $2 -eq 0 ] && MESSAGE="🎄 I'M SO THIRSTY!!! 🎄"
  [ $2 -eq 1 ] && MESSAGE="🎄 I am a happy tree 🎄"
  curl -X POST -F "Body=$MESSAGE" -F "From=+1657wwwxxxx" -F "To=$1" "" -u "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx:yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"

WAITS=$(seq 1 15)

OLDSTATE=$(cat /sys/class/gpio/gpio3/value)


while true

  for i in $WAITS
    # 0 needs water, 1 has enough water
    STATE=$(cat /sys/class/gpio/gpio3/value)
    let "COUNT = COUNT + STATE"
    sleep 1
    echo $COUNT

  # only message on consistent change
  if ! ((COUNT % 15))
    if [ $STATE -ne $OLDSTATE ]
      text $RAY $STATE
      text $KATE $STATE

sleep 1

Finally, a simple modification to /etc/rc.local, add these two lines before “exit 0”

/root/tree/monitor/sh &

That’s it! Super easy and fun, and no tree fires!