Help with low voltage alarm circuit, Please!

Discussion in 'The Projects Forum' started by Telewanger, Aug 3, 2008.

  1. Telewanger

    Telewanger Thread Starter New Member

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    Hi,

    I am a commercial plumber in North Carolina.

    I have invented a 9 volt, magnetic reed switch activated, two conductor, high wet well alarm system. It was simple for a non electronics minded person.

    The alarm is 108 Decibels. It has a push to test battery switch, and works great!

    I need to put a low battery warning chirp circuit in it, so that it chirps like a smoke detector when the battery gets low, and needs to be replaced.

    I called all of the smoke detector companies and they will not give out this information. They said that it is properiority information.

    Does anyone know how to make one, or where to purchase such a circuit for a 9 volt project?

    I would really appreciate any info! :)

    Thanks,

    Mike
  2. Audioguru

    Audioguru New Member

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    A modern smoke alarm doesn't use a 100 parts. It uses an IC that was designed for a smoke alarm that has a low battery voltage detector built-in. The IC has 100 parts all in one.

    You could make your own low battery detection circuit with about 10 parts but it would be on all the time and it would quickly kill the battery. By adding another 10 parts then the low battery detector would be asleep most of the time then wake for only a moment occasionally to detect the battery.
  3. SgtWookie

    SgtWookie Expert

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    Another possibility is to use a microcontroller, set to sleep most of the time - just wake up every few hours, check the battery level quickly - if it's OK, go back to sleep. Otherwise, set the alarm clock for 10 minutes, give a chirp, and hit the snooze button.

    Unfortunately, 9v is beyond the supply voltage of the uC's that I'm familar with. Basic Stamps can run from 9v due to having an internal voltage regulator, but the regulator would run the battery flat in no time.
  4. AllVol

    AllVol Well-Known Member

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    Why does the sensor have to run on 9 volts? Wouldn't 5V do just as well? Perhaps the alarm itself would have to be reworked, or use a separate supply.:confused:
  5. Audioguru

    Audioguru New Member

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    Have you ever seen a fairly small 5V battery?
  6. AllVol

    AllVol Well-Known Member

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    Who said it had to be small? I don't recall that spec. At any rate, three AAA's would last years when a PIC is asleep 99% of the time, and some PICs are designed to run on less than 4.5.
  7. SgtWookie

    SgtWookie Expert

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    A PIC12F675 can run on from 5.5v down to 2.5v with the A/D converter enabled at 4MHz. That uC would have plenty enough horsepower to do the trick - if it's not subjected to overvoltage. 6.5v is absolute maximum.

    I suppose a forward-biased standard silicon diode could be used to allow it to run with 4 AA's or AAA's.
  8. Telewanger

    Telewanger Thread Starter New Member

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    Hi,

    I used to work for US Air, on small turbo prop planes, so I know a little bit about DC voltage, but not much. This is how I knew how to make the alarm.

    Some of your suggestions sounds like Chinese to me. :confused:

    I know that I can buy a smoke detector with press to test and a low voltage warning for around $8.00 to $15.00, and the smoke detector runs off of a 9 volt battery.

    It will be necessary for my device to let me know when the battery is going dead, just like a smoke detector.

    Can I buy this little circuit?
  9. SgtWookie

    SgtWookie Expert

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    Well, the smoke detector alarms use a single proprietary IC to detect the output from the sensor, sound the alarm, monitor the battery voltage and provide the "push to test" function. There are very few actual components.
  10. RiJoRI

    RiJoRI Well-Known Member

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    How about feeding Vbatt into a comparator -- when the voltage drops too low, it trips a 555 driving a sounder?

    --Rich
  11. KMoffett

    KMoffett Senior Member

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    Years ago I implemented a one-chip low 9v-battery detection circuit for a multiple IV-pump to nurse call alarm. The circuit required 2 resistors and one MAX8211 chip ($2.50 from Maxim now).

    http://datasheets.maxim-ic.com/en/ds/MAX8211-MAX8212.pdf

    The current for the chip was ~10µA, plus 15µA for the voltage divider. This was a steady low-on-alarm output though. An 8-pin PIC would my choice for Telewanger's circuit now.

    Ken
  12. lrac

    lrac New Member

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    Hi Telewanger, &/or other members that could help; i to am looking for a 9 volt batt sensor. also a 9 volt / 60 sec push button on/off switch. this i need for a invention i am putting together. i was wondering how you are making out with your sensor? if you would please let me know were & or who you get yours from would be much appreciated. here is my e-mail <snip> THANK YOU & GOOD LUCK. P.S. if i get 1 i will try to contact you threw here if nessecery..

    Moderator's note: It is best to run questions and answers through here, as these are public forums.
    Last edited by a moderator: Dec 5, 2009
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