Landline control?

Discussion in 'General Electronics Chat' started by windsunh2o, May 31, 2014.

  1. windsunh2o

    Thread Starter New Member

    May 31, 2014
    Hi all,

    I'm new to this forum, and newly back to the forum game in general. Lately have been finding most the answers I need with Google alone. This one's different, because I am finding I don't know what to Google for...

    My electrical understanding is mediocre at best. I know how to read a schematic, know the symbols pretty well, and can build a simple circuit off one. I have the hardest time understanding how all the parts work together, which is why I come to you. And this is all just so you know how to talk to me, me being new and all.

    So here's my situation...And in exchange for your generous help, you are welcome to use my concept, ineffectual as it may turn out to be, however you want, and make billions of dollars off it (and am I getting delusional here?)


    I've been thinking of ways I could remotely control the solenoid-based watering cycles of an irrigation system without expensive WIFI-controlled equipment. And I may have come up with something, I just need some help with the circuit theories. I imagine they would be pretty simple, and am guessing 555 timers could be used for a lot of it.

    Here's the basic concept:

    A regular land telephone line would control a relay which controls the solenoid valve which lets water run to the plants.

    This would require a countdown timer circuit that would open the valve for a few minutes and shut itself off.

    The phone line would be called, and hung-up while it's ringing. I have discovered that when a land phone line is dialed and hung-up, the normally-constant voltage drops from 50vdc to 0 (or nearly 0) for a second, then goes back up to 50vdc

    Therefore, the trigger mechanism could be a voltage drop detector circuit that would activate the countdown timer circuit when it detects this drop.

    To prevent unwanted activation by random calls, another circuit would need to be included that allows activation only when the voltage drop is detected twice within the same minute (I would call, hang-up, then call back and hang-up within the same minute to activate the solenoid and countdown timer.)

    So I need to find and build these circuits:

    1) One that will detect the voltage drop of a phone line when it is hung-up (about 50vdc to less than 10vdc)
    2) One that will activate a countdown timer only when 2 of the same voltage drops are detected within 60 seconds of each other
    3) The countdown timer itself, which would close the circuit for a relay for 2-3 minutes, then open again.

    Thank you for reading and for any help you can share! I will also share any progress I make with this...based on the help you are able to provide. Breadboard is ready! Thanks again.

  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    There are numerous "telephone remote control" devices out there.. They feature microcontrollers to allow certain keys to turn stuff on and give statuses,etc... Thats the way to go.
    You must be very careful when "intercepting" phone line voltages.. The phone companies don't like people screwing with that.
    and many more in all price ranges.
  3. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    I agree. Touchtone remote controls have been around for a loooong time because they are reliable and repeatable around the world. The voltage drop you've seen might not be there next week, or when caller id is added to the service, or or or. Plus, this country has hundreds (maybe thousands) of small phone companies, and there is more than enough wiggle room in FCC and ITU rules for incompatibilities.

    Still, I'm gonna look at my own lines and see if the dropout is there...

  4. inwo

    Well-Known Member

    Nov 7, 2013
    If you already have an answering machine, I would suggest coupling a tone decoder to it. Acoustically even, then no worry about telco rules.

    It could be simple for one function. Say just a long "8" or such pulling in a relay.

    Here is a simple tone on tone off schematic.
    Last edited: May 31, 2014
    windsunh2o and absf like this.
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Good point about the telco rules.

    If you go acoustically, it would be very easy to detect the loud phone ringing sound?

    Somehow i have a feeling the O.P doesn't want to have a phone at the receiving end.
  6. windsunh2o

    Thread Starter New Member

    May 31, 2014
    @mcgyvr: Thanks for that product link...I had searched for devices like that one and hadn't turned up much. One I saw would have been close to $500 with all the components! That $50 unit is much more reasonable. I searched Amazon a bit more to look for the other units you mentioned and couldn't find anything else...any others you know of that are around that price range or lower? Or what keywords should I use in my search to yield better results?

    @AnalogKid: Good points that I was unaware of...I need this to be fail-safe, so potential inconsistencies are a definite deal-breaker! And I don't want to risk any trouble with the phone companies. Let us know if you do your drop-out tests...

    @inwo and THE_RB: I am open to using a tone decoder, and am also fine with having to have a telephone/answering machine connected. Whatever works!

    Thanks everyone for your ideas...I will be looking into all of them. If anyone else has suggestions, please keep them coming!

  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009