Relay Circuit

Discussion in 'The Projects Forum' started by virus86, Jan 11, 2011.

  1. virus86

    Thread Starter New Member

    Jan 11, 2011
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    Ive never worked with a relay before and I need some help. I have a Cooler Master Scout computer case. There is a built in switch on the front panel I like to use. It is originally used to turn on/off LED lights on the case fans. I did some measurements on my multimeter and it is supplied by 5V and is rated at 0.5W.


    I want to add this to my case and implement the front panel LED switch to turn it on an off. This is where this relaycomes in. According to the specs, the switch should be able to handle it.

    I made a sketch on what I want to do.
    [​IMG]

    Do I have to put a load/resistor in parallel with the relay coil? I dont know the exact pin layout of the relay, so I may have to change this diagram.

    Thank you.
     
  2. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    No, but it's always prudent to add a protection Diode across a relay coil. Cathode to + side of coil and Anode to - side of coil.
     
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  3. virus86

    Thread Starter New Member

    Jan 11, 2011
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    "Protection Diode"? In what circumstance is that useful? Is there anything like that at Radio Shack?
     
  4. virus86

    Thread Starter New Member

    Jan 11, 2011
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    Okay. I read up on relays and the diode help some voltage peak in the coil.

    I updated my drawing. I have a few P/N: 1N4148 diodes on hand. Can I use them? They have the stats

    FEATURES
    •Hermetically sealed leaded glass SOD27 (DO-35) package
    •High switching speed: max. 4 ns
    •General application
    •Continuous reverse voltage: max. 100 V
    •Repetitive peak reverse voltage: max. 100 V
    •Repetitive peak forward current: max. 450 mA.

    If not, can is use this diode?

    [​IMG]
     
    Last edited: Jan 11, 2011
  5. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    The 1N4148 is a switching Diode and not typically used in this application. In a temporary pinch I would use it, but the 1N4005 (in your link) is power rectifier and more typical for protection Diode applications too.
     
  6. virus86

    Thread Starter New Member

    Jan 11, 2011
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    Thank you! Time to start building! (When I get all the parts)
     
  7. CDRIVE

    Senior Member

    Jul 1, 2008
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    Whoa! Before you go wiring anything,... I must admit that your schematics (more pictorials than schematics) leave much to be desired. I see references to LEDs but I don't see any limiting resistors. Can you redraw it as a schematic?
     
  8. virus86

    Thread Starter New Member

    Jan 11, 2011
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    I dont know how to make a schematic. The last circuit program I used was P-Spice and that was 6 years ago. I used different names in my drawing. There are no LEDs in my circuit. Its basically a 0.5W switch on a 5V line (between the 5V case molex and 5V 2-pin connections) and I want to control a 12V device using the relay.

    [​IMG]

    My end result. I had to break apart a breadboard I already have. A small BB was at Radio Shack for $9! It was hard to get 18AWG cable in to the BB. Its ugly, but it works. I tested it on a 12V/65mA fan.

    [​IMG]
    [​IMG]
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
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    Ouch! 18AWG is way too large and will damage the contacts on a ProtoBoard. Cat-5 or CAT-3 cable conductors make excellent conductors for a ProtoBoard. In your case, you should have tack soldered it to your cable. Other than that, I guess you're good to go.
     
  10. virus86

    Thread Starter New Member

    Jan 11, 2011
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    I was able to get the 18AWG into the BB by only inserting a few of the little wires. Solder? Id like to avoid it.
     
  11. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Alternatives to soldering are small wire nuts, or crimp butt connectors.
     
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