Christmas tree low-water monitor

The end of the year is rapidly approaching and there’s a good chance you have a slowly dying tree in your living room. Help it hold on a little longer by using [Eric Ayars'] Christmas Tree water monitor. He’s built a sensor out of a piece of strip board. Three bus strips on the board allow for a variety of alerts. When all three are submerged everything is ok. When the two longer traces are still under water but the third is not an LED will blink to let you know it’s time. If you don’t pay attention and there’s no water left, a piezo buzzer makes noise until you add water (or the coin cell runs out of juice).

This project centers around an ATtiny85 that [Eric] programmed using an Arduino, one of the methods we covered in our AVR Programming Tutorial. But if this simple circuit isn’t high-tech enough for you, we saw a similar method last year that will send an alert to your iPhone.

Comments

  1. Pouncer says:

    This is something I definitely need to build. I’m forever forgetting to water the tree.

  2. isama says:

    or you could just buy a fake tree. it doesn’t lose its “leaves” and needs no water. and it lasts for 10+ years.

  3. Dave says:

    Shoot. This just reminded me that I forgot to water the tree :(

    So I guess it works.

  4. Ivan says:

    Same problem I’ve seen with other water level monitors, It won’t work.

    It will work at first, but as there is constant current DC (even if small) through the electrodes, they will corrode and react to electrolysis, and eventually if they are on the same board, let the current pass though even when it’s dry.

    Humidity sensors are not that simple, even for an ON/OFF sensor, an AC current must be used to avoid crystals forming on the electrodes, whose material should be also carefully chosen.

    Believe me, you will be throwing the sensor to the garbage by February.

  5. klulukasz says:

    @Ivan
    I dont think it was supposed to last longer then for one Christmas… he could have used avr’s sleep mode so the batteries would last much longer as now it is using few mW all time

  6. sam says:

    Hes not using coin cell batteries…..those are AA batteries

  7. smoker_dave says:

    I made a much more simple moisture level detector a while ago. It is so simple that any person can make it. Really just two transistors, an LED and limit resistor.

    Check it out here:
    http://wilson479.spaces.live.com/blog/cns!ABB4BD954AB126DB!495.entry

    The version in the write up uses a solar cell I had laying around but you could stick and kind of battery on there. Just modify the limit resistor to suite.

    For calibration, just move the probes in the soil so they are bordering on LED on / off after watering.

  8. Luke says:

    Even the atiny seems like massive overkill. I can imagine a lot of circuits right off the top of my head that don’t involve a uC. Like a 555 to make a piezo start beeping when the water gets low, or even just a single switch to turn on the piezo when the water is low. I’d skip the electric measurement and just use some kind of hand-fasioned floating switch (think toilet or gas tank)

  9. aaa says:

    guys, just take a look at the water level every couple of days ;-)
    advantage: cost 0
    disadvantage: no hacking

  10. therian says:

    Ivan is right, such design mistake is forgivable to 1transistor circuit but with uC there is no reason not to implement AC current

  11. Kemp says:

    So these days we use microcontrollers for these types of circuits… interesting.

  12. Alex Rossie says:

    1) A µC for this really? Cheap µCs are making your hacking skills flabby.
    2) Being submerged in water is a no no.
    3)
    A transistor with it’s base attached to a probe into the soil and another probe coming off + would be far more effective.

    A pot connecting ground to the base probe can control sensitivity.

    Parts:
    transistor try BC549
    LED anyone will do Green is good (super bright means no rsistor needed)
    Resistor (optional current limiting)
    Pot (or resistor sensitivity control. optional)
    some wire and solder

    cost? Well if you don’t have 2 resistors an tranisistor and led lying around then you wouldn’t be here.

  13. Alex Rossie says:

    °+ GND
    | |
    | |
    | |
    |\_/—-|>|—/\/\/\-|
    | |———–/\/\/\-|
    | |SOIL
    ^ ^
    Not bad for an ascii art schematic!

  14. gregman_1 says:

    I agree with Alex Rossie and Kemp. I get pretty annoyed seeing uC’s where a solid state circuit would be so easy and effective. It’s like you guys aren’t even trying anymore.

    I’m sure you guys will remember that at one time, there was no such thing as microcontrollers and circuits like this were built all the time (ask my 59 year old hacker dad). So taking old-hat solid state projects and building them with a microcontroller is like taking a step back in skill.

    C’mon, HAD, you can do better than that.

  15. japkin says:

    If you’re going to use a microcontroller for something like this, at least have it SMS you or post a Tweet.

  16. nanomonkey says:

    The roomba usually tops off the tree after cleaning up dead needles.

  17. SkippyHunter says:

    Quote : aaa

    guys, just take a look at the water level every couple of days ;-)
    advantage: cost 0
    disadvantage: no hacking

    Response :

    That’s the spirit aaa, why not just purchase all of your products and watch TV instead of using your brain! It’s silly to be creative, no?

    Hey wait, isn’t this site all about being creative? Nah, you are dah man, aaa.

  18. Daniel says:

    Give him a break about the microcontroller. They are a great way for someone without a lot of electronics knowledge to build a simple circuit. If you want to hack your own christmas tree, feel free to post about how you did it with a 555. Just don’t expect him to do it the way you want it done if you aren’t willing to do it.

  19. Eirinn says:

    @isama yes also plastic presents and plastic entertainment – while we’re at it, plastic food would also be convenient. It will look nice and people can just eat porridge :)

  20. Eirinn says:

    Warning, ubergeeks present that will whine that this isn’t made using a lemon, 2 electrodes, a piezo and some diodes/transistors.

    No really this is a nice, affordable project that can be done by anyone. If you feel this could be done easier then please by all means do post a tutorial.

  21. Squirrel says:

    Easier way:
    1. Make a float (out of whatever’s at hand… glue stick without the innards might work, be creative)

    2. Have the float make some contact (or pull a string that makes some contact etc) when the water gets below a certain point.
    When the contact is made, it will complete a circuit driving an LED. Another contact and the same float could even be used to drive the buzzer

    Advantages: No electrolyzing problems, no uC, cheap
    Disadvantages: moving parts

    Or you can use an arduino and a sonar module :)

  22. macw says:

    Everyone who complains that they could do this with a lump of quartz and a lemon battery with both eyes closed and one hand tied behind their back — why don’t you do it already? Post some of these simple circuits so that the readers can actually learn basic analog electronics, instead of bitching that nobody knows the old ways. Guess why they don’t: because all the people who know them are cranky, arrogant old farts who act like teaching a newbie is beneath them.

  23. Alex Rossie says:

    @macw, I did I tried to draw a schematic using this comment but it removed the multiple white spaces.

    So… we’ll accept your apology when you’re ready.

  24. jeditalian says:

    since platinum electrodes are most likely out of question, take some old AA/AAA whatever, just some batteries, rip them open, remove the graphite/carbon core and scrape it clean with a knife. voila! non-corroding electrodes!

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