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Thread: Timer Circuit

  1. #1
    Variable Bitrate Fox_Mulder's Avatar
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    Timer Circuit

    I don't the right place to post this but I'll try my luck here:
    I'm looking to build a timer for a pump.
    I want the pump to run for 5 minutes, then shut of for 1 hour.
    I also want to add a thermistor to prevent the pump from overheating.

    I've tried using a 555 timer as an astable circuit with a HIGH output time of 3600 seconds and a LOW output time of 300 seconds but this didn't seem to work as the resistor values I would need were huge and I dont think the 555 timer copes well with times over 10 minutes.
    Cycle:
    Pump Runs for 5 mins
    Cools for 60 mins
    And the cycle repeats, but the thermistor must be included to prevent the pump from overheating. So when the Thermistor circuit outputs a high, the 555 timer circuit should jump to the "Cools for 60 mins" stage.

    Does anyone know of a cheap way of getting this to work? Or a simple way of reducing the speed of the induction motor/pump to cool it down and allow it to run for longer?
    Fox Mulder
    2004 Toyota MR2
    Intel Dual Core 2.0Ghz 1Gb DDR2 160GB SATA2 M4ATX Lilliput 7" TS BU353 DiNovo Mini Car2PC ODBII Bluetooth HF 16x2 Character LCD

  2. #2
    lez
    lez is offline
    FLAC lez's Avatar
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    7555 ? (cmos 555, should do an hour, use large capacitor to overcome large resistor problem)
    Lez, more widely known as flez1966

  3. #3
    Variable Bitrate Fox_Mulder's Avatar
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    Won't the large cap have a larger current leakage problem?

    I think I might use a 4017 decade counter with the 555 timer, where the timer will send a pulse every 5 mins.

    I'll have the Pump on the 2nd last output of the decade counter, and have the thermistor circuit wired to the RESET pin on the counter. (The Last Pin is also wired to RESET). The other Output Pins will all just be grounded, or tied to a led etc. When the thermistor senses it's too hot, the RESET pin then goes high and the counter starts from the first output. Causing a delay of 40 mins untill the pump is turned on again. Otherwise when 5 mins are up the pump will be allowed to cool for 40 mins anyway as the counter is reset by the timer moving the cycle forward.
    Fox Mulder
    2004 Toyota MR2
    Intel Dual Core 2.0Ghz 1Gb DDR2 160GB SATA2 M4ATX Lilliput 7" TS BU353 DiNovo Mini Car2PC ODBII Bluetooth HF 16x2 Character LCD

  4. #4
    Variable Bitrate Fox_Mulder's Avatar
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    Here's a Schematic I conjured up in paint:
    (R = ohms)

    [Schmatic is wrong, it shows the poer supply of the 4017 comming through the resistors!]
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    Fox Mulder
    2004 Toyota MR2
    Intel Dual Core 2.0Ghz 1Gb DDR2 160GB SATA2 M4ATX Lilliput 7" TS BU353 DiNovo Mini Car2PC ODBII Bluetooth HF 16x2 Character LCD

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