Keeping relay closed

Discussion in 'General Electronics Chat' started by ivars211, May 5, 2013.

  1. ivars211

    Thread Starter New Member

    May 5, 2013
    Hello everyone,

    I am trying to make a garage security system with GSM. I have bought one of these cheap Chinese alarms and wired my Nokia 3310 like this. I wanted to connect phone's button to alarms beeper, so when it rings - button are being pressed. But I run into problem - as beeper has a tone, it keeps sending interrupted signals, so button is being pressed and released very fast. To make it dial (fast dialling) it should hold button at least for 1 second.
    I was wondering if there are any way to delay given signal so that relay keeps closed at least for a second, instead of clicking on and off.

    I would appreciate any suggestion.
    Thank you!

  2. ivars211

    Thread Starter New Member

    May 5, 2013
    Sorry, I did not find edit button, so I made a reply.
    After several hour looking through different circuits I found this:
    Could someone please confirm that this would work?
    I would replace Piezo Wafer with relay/transistor that connects my Infrared Remote alarm's beeper and change Piezo Sounder with relay that connects to my Nokia 3310 button.
    Thank you in advance.
  3. Mike33

    AAC Fanatic!

    Feb 4, 2005
    Well, yes, it will work, but you may have to alter some of the component values.

    Google "basic LM555" or "LM555 tutorial", and learn how they work! With just a couple of R's and C's, you should be able to create a circuit that will trigger and HOLD your relay closed for a specific output time. You may need to use a BJT to invert the signal you are inputting to the 555 (it triggers on a Negative going pulse! You would hold it H until your 'event' occurs, which, when a voltage is output from your device will invert the H to a L, tripping the 555). Not so hard to do, and you will learn much about the 555!

    Let us know how you're making out.
    ivars211 likes this.
  4. massimj

    New Member

    May 5, 2013
    You could use a 8 pin PIC, and the free version of PicBasic to program it. The PIC might cost $1.00, maybe more depending where you buy it. It has one ADC in it, and a Timer. It can be run with its built-in RC OSC, so no crystal, or Resonator unless you need very accurate timing. With the PIC, you can program it to do any kind of logical operation. It can be based on time, or external input. The skill you gain from using that 8 pin PIC will enable you to use PIC's for other projects, and use more powerful PIC's, using the same knowledge you gain from using the simple 8 pin PIC. There are lots of programming examples all over the internet. Good luck.. Joe
    ivars211 likes this.