Relay Circuit with LED - Critique my schematic

Discussion in 'The Projects Forum' started by Phrazemaster, Dec 3, 2010.

  1. Phrazemaster

    Thread Starter New Member

    Dec 3, 2010
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    Hi folks, very pleased to have found you!

    I'm building a microphone preamp, and I'm going to use a SPST switch to drive a relay and LED circuit for visual feedback that certain functions are engaged. I'm new at all this, so please bear with me.

    I am posting a schematic here of my proposed circuit:

    relay-circuit2.jpg

    In question is the relay branch. The relay specs say it is a 12v relay with 1028R coil resistance and nominal operating current of 11.7ma. I'm assuming I have to drop the volatage 3v, although I could just run the relay at 15V. I'd like it to last a long time. Does this resistor take care of it? How do I go about choosing the coil protection diode (like what values?). I have heard 1N400x, but still being new this didn't do much for me. Do I have the coil protection diode facing correctly?

    REally dumb question, I'm sure, but how can I be certain the relay only takes 11.7ma of current...I've got an electronics book on the way from amazon.

    Does this circuit look viable? Any problems you can spot?

    Thank-you. I know this is basic.
     
    Last edited: Dec 3, 2010
  2. ashish19183

    New Member

    Sep 16, 2009
    13
    0
    Hi,

    relay protection diode can be any flyback diode, it used to save connected device from back EMF

    Regarding your current 11.7mA its coil current not not load current... means coil is connected with your input and switch is connected to your output, here coil current is given and switch current is different from this.

    Main point why you are using relay to run LED ... LED have very low current o/p so you should go with Transistor based circuit which is easy, take less power and life is more than relay .....
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    It looks OK, the only critique I would offer is how you label your resistors. I know it is a format for some countries, but it is better to keep it simple. Something like this...

    [​IMG] [​IMG]

    I've been doing this for a while, and can't understand the values you trying to show.

    Also, designations can be critical. If I referred to R5 on the first schematic you would know exactly what resistor I was talking about, without long winded descriptions.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    But, by referring to 'R2' you might cause some confusion...

    :)
     
  5. Phrazemaster

    Thread Starter New Member

    Dec 3, 2010
    15
    0
    I appreciate the feedback.

    @ashish19183:

    Probably my poor schematic was misleading, but I'm not running the LED off the relay; the relay is there to be a DPDT switch for other parts of the preamp. I could have made this all a lot simpler with a 3PDT switch, but they didn't make one in the style I want to use (well that's a lie; it was $70 each! Times 8!).

    So I don't really know how to accomplish this with a low component count IC based solution, but if there is one that would be fine.

    @Bill_Marsden:

    If that monster circuit you posted is what I think it is...a momentary pushbutton controlling a relay? Is that a latching relay, and how does this circuit work?

    Thank-you again for your kind attention.

    Mike
     
  6. tyblu

    Member

    Nov 29, 2010
    199
    16
    Looks good! Ensure the flyback diode is called 'high speed' or similar in the datasheet.
     
  7. Phrazemaster

    Thread Starter New Member

    Dec 3, 2010
    15
    0
    Fantastic, thank-you! It's folks like you and the others who post that make learning so much easier, practical and fun.

    Is there anything specific I should look for in terms of voltage...the psu is only 15v...i'm assuming higher voltage is better? The tip about high speed is awesome!

    Thanks,

    Mike
     
  8. bazli

    New Member

    Dec 4, 2010
    2
    1
    the 1k ohm resistor that you put before the led..it is much better to get 270 ohm...i have been tried
     
  9. Phrazemaster

    Thread Starter New Member

    Dec 3, 2010
    15
    0
    Thank-you. Is that because it made the LED too bright?
     
  10. Phrazemaster

    Thread Starter New Member

    Dec 3, 2010
    15
    0
    By the way, I'm just wondering what software you use or recommend for making schematics. I cobbled mine together manually in Illustrator, but as you say, it's better to use the expected symbols. I used what I thought was right, but I know there's a ton of great stuff out there for making schematics.

    What do you recommend?

    Thx,

    Mike
     
  11. tyblu

    Member

    Nov 29, 2010
    199
    16
    It's really up to the datasheet for your LED. 270-ohm will let 56mA through; 1150-ohm will let 13mA though.

    Of the free versions, I've used EAGLE, LTSpice, and am now getting to know gEDA to draw schematics. EAGLE and gEDA can also do PCB layout, though you will inevitably have to create your own layout specifications at this step as their libraries are far from complete.
     
  12. Phrazemaster

    Thread Starter New Member

    Dec 3, 2010
    15
    0
    Thanks for the info tyblu. I'll check it out.
     
  13. Phrazemaster

    Thread Starter New Member

    Dec 3, 2010
    15
    0
    OK, in trying to lay this out for actually building, I realized what I was creating looks a little different from the schematic...and I'm not sure if they are equivalent!

    Can anyone tell me if this:

    relay-circui3t.jpg

    Is the same as this:

    relay-circuit-same-question.jpg

    Thanks for your wisdom.

    Mike
     
  14. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    No, the bottom picture has shorted the relays, so that will not function.

    Bertus
     
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  15. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I draw my schematics with a set of templates I've made over time. I cut an paste to a M/S Paint file, but any graphics program will work. The schematic I used as an illustration was a delayed timed relay I drew for someone else on this site. I draw a lot of schematics, most of them even work.

    If you are interested you can get a copy of PaintCAD from here. I update it periodically, which zero's the download counter. It is due one now.

    Introduction and PaintCAD

    Bill's Index

    Bill's Albums
     
  16. Phrazemaster

    Thread Starter New Member

    Dec 3, 2010
    15
    0
    Thank-you Bill for the info, and for the links. I will check them out! :D
     
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