Make: Electronics Experiment 7 (Relay-Driven LED)

Discussion in 'Homework Help' started by OgreSwamp, Jan 18, 2015.

  1. OgreSwamp

    Thread Starter New Member

    Jan 18, 2015
    2
    0
    Hi there,

    I'm reading Make: Electronics to recover my college electronics knowledge.
    I've assembled a circuit (using a breadboard, during it with alligators is a nightmare) and it doesn't really work.

    So here is a circuit I'm trying to do:
    [​IMG]


    Here is what I've done:
    [​IMG]

    Resistor is 680Omh, LEDs positioned properly (cathodes facing right - to the negative, green wires).
    When I press red button (bottom left corner) I can hear the relay is switching, top led goes off, but bottom one doesn't start.

    I've tried few things:
    1) replace a relay component
    2) replace LED
    3) tried to measure voltage at 2nd led pins when I press red button

    1 & 2 doesn't help.
    Voltage goes up to 0.4-0.6 for half a second and then drops to zero when I press/release the button.
    Can't figure out what's wrong. My only guess was that DPDT relay I've bought isn't the correct one, but I found the data sheet and it says that coil voltage is 12v - came as my circuit voltage.

    Here are few more pictures to get a better understanding what's happen there.
    [​IMG]

    [​IMG]

    [​IMG]
    Thanks!
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,564
    2,379
    Do you have the relay Common contact wired correctly and not to the N/C contact?
    Max.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
    3,834
    Try flipping g the non-working LED (it may be reversed in your circuit).
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,564
    2,379
    I just checked the relay and you have it connected up wrong as I suggested, the relay common contacts are nearest the coil terminals.
    Max.
     
    GopherT likes this.
  5. OgreSwamp

    Thread Starter New Member

    Jan 18, 2015
    2
    0
    Thanks Max, that actually worked. I switched red probe from push button & non-working LEDs anode and now everything is working!
     
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