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I'm completely brand new to electronics and just bought a breadboard kit to try and get my feet wet. I have a 9V battery and I'm trying to fire up a green LED.

I have a 330 Ohm resistor in series with the LED and if I measure the current coming out of the resistor I'm only getting about 4.5 mA, and I think I need at least 20 mA to fire up the LED. See the attached picture.

What is not visible in the picture is that the red wire is connecting to an output that reads 5V.

If I connect the LED directly to the Elegoo board it lights up fine. Any suggestions?![enter image description here]1

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    \$\begingroup\$ you have to share how the connection is made in a drawing. it is really importatnt to save others time and helps you to get quick useful response. picture is blank. 4.5 mA is really okay to fire a normal LED. \$\endgroup\$ – User323693 Aug 30 '19 at 21:53
  • \$\begingroup\$ @Umar sorry and thanks! I’m trying to get the picture uploaded now \$\endgroup\$ – hax0r_n_code Aug 30 '19 at 21:53
  • \$\begingroup\$ if you have trouble, share the link. one of us will upload it for you \$\endgroup\$ – User323693 Aug 30 '19 at 21:54
  • \$\begingroup\$ @Umar finally got the picture to work \$\endgroup\$ – hax0r_n_code Aug 30 '19 at 23:21
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    \$\begingroup\$ It looks like one resistor lead, both LED leads, and the white wire are all in the same horizontal row of the breadboard - that group of holes arfe all connected together, so the LED is shorted. You appear to exepect a connection between holes b and c, but no connection between c and d. Put the resistor lead and one LED lead in one row, and the other LED lead and the white wire in the next row, so the LED won't be short-circuited. \$\endgroup\$ – Peter Bennett Aug 30 '19 at 23:46
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Peter Bennet put his finger right on it in the comments.

The way breadboards are built, the pins where you have your LED and the resistor connected together are all shorted together.

Your LED could straddle the gap in the middle, or you could use two parallel rows.


Bruce Abbott pointed you at a tutorial for breadboards for this very reason. The diagram on the page he linked to clearly shows how the pins are connected:

enter image description here


As to the current your LED needs:

The 20mA you mentioned is most likely the maximum current allowed that will not destroy the LED.

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  • \$\begingroup\$ Thanks for your answer. I can’t say I still completely understand why straddling the LED between two rows works and the other way didn’t. I know you explained that everything on the same row is shorted together (which is the part I don’t understand). It just seems to me like the current is doing the same thing in my previous setup and this one. \$\endgroup\$ – hax0r_n_code Aug 31 '19 at 9:56
  • \$\begingroup\$ See that row marked in blue in the picture? That's where you had your LED plugged in. Imagine the blue thing is a wire (because it is a wire.) You had both legs of your LED connected together. The current just flowed right past your LED without going through the LED. \$\endgroup\$ – JRE Aug 31 '19 at 10:02
  • \$\begingroup\$ got it! Perfect explanation. Thank you! \$\endgroup\$ – hax0r_n_code Aug 31 '19 at 10:14

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