Really basic LED/breadboard question

Discussion in 'Homebrew and Kit Projects' started by KT5MR, Aug 14, 2020.

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  1. KT5MR

    KT5MR Ham Member QRZ Page

    Hi all,

    I am missing something utterly fundamental here. I have assembled a basic circuit on a breadboard, consisting of a 220 ohm resistor, an LED, and a 5V power source (an Arduino actually).

    Here is what I have. Assume the red wire is connected to a positive side of the voltage source and the black wire is connected to the negative side. In this configuration, the LED lights.

    Screen Shot 2020-08-13 at 5.56.13 PM.png

    However, if I rotate the LED and put the ground wire in what I believe to be in series with it, the LED does not light (had to rotate the board as well to make it clearer what had changed):

    Screen Shot 2020-08-13 at 5.57.53 PM.png

    I do not understand why the LED does not light in the above configuration. In my mind, the power comes in through the red wire, flows across the five-hole horizontal bus to one end of the resistor, flows through the resistor to the other end, flows across the five-hole horizontal bus to the anode of the LED, through the LED, out the cathode and to the black wire connected to ground.

    Whatever am I missing?
  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    The lines of 5 holes are connected together.

  3. KB7WG

    KB7WG Ham Member QRZ Page

    Wrap the tail of a couple of resistors around your meter probes, and measure the resistance of the breadboard holes......on an un-powered board. You can mark the common holes with a marker until they become embedded in your mind. Bread-boarding is extremely important, but a cheap broad can ruin the experience. Search for 2020 breadboard reviews and purchase a quality board.

    Have fun.
  4. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Hmmmm.... interesting :rolleyes::D

    N7EKU and KB7WG like this.
  5. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Ding ding ding.

    The 5-hole rows are ALL IN COMMON on a breadboard. In the second photo, the LED is shorted to one end of the resistor, and tied to the black wire. The black and the red are connected directly to the resistor. The LED only sees the negative wire but on both of its pins. Of course nothing will light :)

    OP needs to use the outer rows for the power buss - one for plus and one for minus. That's what they're there for

  6. KT5MR

    KT5MR Ham Member QRZ Page

    OH I GET IT!

    Wow a light bulb (LED?) just went off in head. Absolutely, they are all connected each the same time.

    For some bizarre reason I was "following the current" and thinking it went to hole one, then to hole two, then to hole, all five holes are, as Dave just said, connected in common. I get it....I'm connecting both leads of the LED to the ground lead. Well, that certainly won't work.

    Thanks yall for answering such a basic question. My journey in electronics continues. :)
    N8TGQ, WA4SIX and W7UUU like this.
  7. K6BSU

    K6BSU Ham Member QRZ Page

    Turning the board over will instantly indicate which holes are common. I would do that BEFORE placing components.
  8. KF5FEI

    KF5FEI Ham Member QRZ Page

    Breadboard laid out like so:
    W7UUU likes this.
  9. AG6QR

    AG6QR Premium Subscriber QRZ Page

    Many breadboards are mounted to a plate such that you can't see the connections. If you turn it over, you just see the solid mounting plate. But all the ones I've seen use the standard style of connections, as shown in the above posts. A minute with a continuity tester is time well spent for anyone with any doubts or curiosity on the subject.

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