1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Making LED rocker light up when switch ties 5V to GND?

Discussion in 'General Electronics Chat' started by Gigahurtz, Oct 28, 2017.

  1. Gigahurtz

    Gigahurtz New Member

    Joined:
    Oct 28, 2017
    Messages:
    3
    Likes:
    0
    I have a SPST LED rocker switch that is being used to connect ~+3V to GND on a DVR. Doing this turns on the DVR and begins the recording sequence. The problem is when this is done, the potential is nearly 0V and can't be used to drive the built-in LED! If I have an external volage source, is there a simple circuit that would allow me to tie the 3V to GND but also allow the LED to turn on when the switch is closed?

    This is the switch that I'm using: https://www.amazon.com/gp/product/B01HPRZ2O4/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

    Thank you for any guidance!
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,585
    Likes:
    950
    Location:
    Canada, of course!
    The Amazon cheap bunch of switches has a poor Engrish translation of its 12V LED connection to its switch terminals then the LED will not work from only 3V.

    The switch is rated for the very high current of 20A so its contacts must be silver that corrodes soon (turns black) and will fail to switch the low current you probably are using. A high current that you probably do not have sparks away any corrosion.

    For switching low current signals I always use a switch that has gold plated contacts that never corrode. They cost the same or less than high current switches.
    I always buy a switch from a local distributor (Digikey) that has detailed explanations in good English.
     
  3. Gigahurtz

    Gigahurtz New Member

    Joined:
    Oct 28, 2017
    Messages:
    3
    Likes:
    0
    Thank you for the reply - I'll take it into consideration for future builds. That said, I'm still not sure what circuit might allow for a 12V external bias just for the LED, but also enable a connection between the DVR +3V and GND.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. Pommie

    Pommie Well-Known Member Most Helpful Member

    Joined:
    Mar 18, 2005
    Messages:
    10,161
    Likes:
    340
    Location:
    Brisbane Australia

    You can't do it with those switches without a relay. You need a switch that will ground the terminal and the LED.

    Mike.
     
  6. Gigahurtz

    Gigahurtz New Member

    Joined:
    Oct 28, 2017
    Messages:
    3
    Likes:
    0
    I'd prefer to use these switches for aethetics as I've already used a number of them in a project, but don't have this issue since they all work off 12V. How would I set up a relay? Thanks!
     
  7. crutschow

    crutschow Well-Known Member Most Helpful Member

    Joined:
    Mar 14, 2008
    Messages:
    10,623
    Likes:
    479
    Location:
    L.A., USA Zulu -8
    Here's my take on a circuit to do what you want based upon my understanding of the switch.
    It requires the addition of Q1 and R2.

    The LTspice simulation shows current through the LED (D1) when the switch (S1) is closed, which lights the LED and turns on Q1 to short the 3V signal to ground (Vout).
    R1 is an assumed resistor in the circuit and R_internal is the LED resistor inside the switch (switch is inside the dashed line).

    upload_2017-10-30_21-46-45.png
     
    Last edited: Oct 30, 2017
  8. Pommie

    Pommie Well-Known Member Most Helpful Member

    Joined:
    Mar 18, 2005
    Messages:
    10,161
    Likes:
    340
    Location:
    Brisbane Australia
    You would power the relay like any other device and have the relay ground the 3V line. Or, as mentioned above, use a transistor to ground the 3V.

    Mike.
     

Share This Page