Help needed to trigger 12v relay circuit with small voltage from a digital egg timer

Discussion in 'General Electronics Chat' started by joolsh20, Jun 20, 2017.

  1. joolsh20

    Thread Starter New Member

    Jun 20, 2017
    5
    0
    I was wondering if anybody here can help me. I have had some relay circuits built which when a circuit is closed with a button, it triggers the relay which opens a 12v circuit to set off a siren (it has a 5 second timer build in). These are used for our paintball site so when a plastic pad is shot (it has a button behind it) which triggers the siren. They work well a do as they should.
    Now the problem?
    I would like to use a digital egg timer to trigger the relays so when the timer reaches zero the relay work activate and the siren would go off. However the voltage produced by the egg timers fluctuates between .3 and .5v and is not consistent. This does not seem to trigger the relay circuit. I have asked several people about this with no joy, so I was hoping somebody on here might be able to shed some light.
    Thank you all for your time.
     
  2. pars842

    New Member

    Jun 20, 2017
    3
    0
    egg timer's voltage might be insufficient for relay to be triggered. Try to find the minimum triggering voltage of the relay circuit. It may be 3V. You can amplify the egg timer's voltage output with a simple Op-Amp circuit.
     
  3. EM Fields

    Active Member

    Jun 8, 2016
    583
    154
    Please post a data sheet for the egg timer and a schematic showing your relay/timer circuitry and its interface to the egg timer.
     
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,998
    1,355
    Sounds like its an AC signal or square wave, have you measured it on AC, you would need an op amp to boost the voltage.
     
  5. joolsh20

    Thread Starter New Member

    Jun 20, 2017
    5
    0
    Thank you for your quick responses. I do not have a diagram for the egg timer circuit , only the actual timer bought off ebay! I have attached the picture of the relay circuit. I have been told it triggers from 1.2v upto 12v.
     
  6. joolsh20

    Thread Starter New Member

    Jun 20, 2017
    5
    0
    Thanks for the suggestion. 1.2v is the minimum needed to trigger. As for a Op-mp circuit, are these bought off the shelf or better to make on (my skills are limited to basic electronics as you may have figured!)
     
  7. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,998
    1,355
    You can buy op amp chips individually, or a ready made amp pcb for convenience.

    Can you take pictures of the inside of the egg timer.
     
  8. pars842

    New Member

    Jun 20, 2017
    3
    0
    joolsh20 you can easily build the amplifier circuit. as you can see from the image, output of the amplifier circuit will be multiplication of your egg timer's output voltage and ( R1/R2 )+1.

    Vin is your egg timer's output voltage and Vout will be the signal that will trigger the relay.

    [​IMG]

    You have 0.3 V at egg timer's output, but you need at least 1.5V. So 0.3Vx((R1/R2)+1)=1.5V . You can choose R1=4k ohm and R2=1k ohm. This circuit can be built on a breadboard.

    An example to show how easy this is:
    [​IMG]
     
  9. joolsh20

    Thread Starter New Member

    Jun 20, 2017
    5
    0
    What a fantastic response. Thank you so much for all of your help!!!
     
  10. ian field

    AAC Fanatic!

    Oct 27, 2012
    6,543
    1,195
    A sensitive gate SCR might do - most TO92 style can handle a small relay.
     
  11. EM Fields

    Active Member

    Jun 8, 2016
    583
    154
    I'm confused about how you want to use the egg timer. Can you explain in a little more detail how you want it to work, please?

    As I understand it, without the egg timer in there when a plastic pad is shot it'll start a siren which will last until the relay times out, then it'll go silent until the pad is shot again, etc. etc...

    What I don't understand is the egg timer's role in all of this. That is, what would be the sequence of events, and their timing, leading up to the siren(s) being triggered and then silenced?

    I'm also confused by the picture of the relay PCB you posted. If it's a relay which controls a siren, where are the timing components and how is the egg timer connected to the PCB electrically.

    Finally, which egg timer are you using, and can you provide a link to its description?
     
  12. joolsh20

    Thread Starter New Member

    Jun 20, 2017
    5
    0
    The egg timers role is to replace the pad, so rather then somebody having to shoot a pad with a button in it. The egg timer can be set to a certain i.e 3 minutes, then when it reaches zero the siren would go off. The idea is to have a game where a VIP/ captain has to be escorted across a game zone in a specified time and if not the timer counts to zero and their siren goes off.
    The PCB i posted is the relay circuit I use with the pads. I am unsure how to wire the egg timers internal buzzer to activate this relay.
    The egg/ kitchen timer I will be using is something like this:
    https://www.nisbets.co.uk/hygiplas-...&cm_mmc=PLA-_-806851437-_-42653046675-_-DP028
     
  13. ian field

    AAC Fanatic!

    Oct 27, 2012
    6,543
    1,195
    That picture is not the tech info needed.

    A pure guess - it probably has a piezo sounder. If the battery voltage is small, they peak the sounder capacitance with an inductor - that will most likely trigger a sensitive gate SCR. A direct drive sounder disk might not.
     
Loading...