Newbie series LED issue

Projects General Guidance
1

Thanks for reading!

I'm no expert on circuitry or the Arduino and I'm having issues with a project. I have a series of 8 LEDs all with the same ground. When the one farthest from the grounded LED is powered, every LED should light up. When the next farthest one is powered, seven of them should light up, etc. This isn't the case however, as the Nano's 5 Volts of power aren't enough to power more than two LEDs in series. Each of the eight LEDs has its own pin that is supplying it and the next LEDs with power through a diode that blocks the output pins from being used as ground.

I tried testing it from ground up. When I power the second to last LED, it and the last light up as intended. Going up to the next LED, however, doesn't light any of the three that are being powered. I've attempted to supply power to both the pin that should light up all three along with the next that should light the last two, and doing so only causes the last two to light up. I've checked it by connecting the LED third from ground to ground and it does light up when that's done.

Currently I have no clue how to get this to work without having to completely rewire everything which I don't have the time to do. If anyone can explain to me how to work around this issue or fix it somehow it would be very much appreciated!

Thank you!

2

If you don't have time to rewire it, you're out of luck.

Each pin and a resistor can handle 1 led, placing leds in series will not work, too much voltage drop per led.

(Use a shift register, or individual pins for each led, or if you must a higher voltage with transistors)

3

cjdelphi:
If you don't have time to rewire it, you're out of luck.

Each pin and a resistor can handle 1 led, placing leds in series will not work, too much voltage drop per led.

(Use a shift register, or individual pins for each led, or if you must a higher voltage with transistors)

Thanks for the reply. In this case how would you recommend I rewire it?

4

Can I see the circuit? A picture .. or draw a schematic. .. hard to visualize what you've already done

5

I' ve never heard of someone connecting led's in series. Where did you get the idea to do that ? (what nade you think it would work?)

6

cjdelphi:
Can I see the circuit? A picture .. or draw a schematic. .. hard to visualize what you've already done

Hmm... I think I'm just going to attempt to rewire it all with the time I have left. I appreciate the help!

P.S. A picture of this... Thing... Wouldn't help xD

7

Well, there is the hard way.

since each LED has a voltage drop, you could create a variable voltage power supply and just supply the correct voltage to the correct pins.

assuming 20ma for current, you only ever need to supply 20ma, just at different voltages. and at different points.

Sorry that I cannot help you with creating a variable voltage power supply. Sunday night is a school nite and the kid has to get to bed.

8

LM317 and a 24Vdc power supply.

9

raschemmel:
I' ve never heard of someone connecting led's in series. Where did you get the idea to do that ? (what nade you think it would work?)

Surely you have, take any LED strip which takes 12v, or do you mean from an arduino pin?

10

I have a series of 8 LEDs all with the same ground. When the one farthest from the grounded LED is powered, every LED should light up. When the next farthest one is powered, seven of them should light up, etc. This isn't the case however, as the Nano's 5 Volts of power aren't enough to power more than two LEDs in series. Each of the eight LEDs has its own pin that is supplying it and the next LEDs with power through a diode that blocks the output pins from being used as ground.

I tried testing it from ground up. When I power the second to last LED, it and the last light up as intended. Going up to the next LED, however, doesn't light any of the three that are being powered. I've attempted to supply power to both the pin that should light up all three along with the next that should light the last two, and doing so only causes the last two to light up. I've checked it by connecting the LED third from ground to ground and it does light up when that's done.

Everything in the above statement says all eight leds are being run from the Nano's 5V

This isn't the case however, as the Nano's 5 Volts of power aren't enough to power more than two LEDs in series.

Given that it is no secret the voltage drop accross a led is in the ball park of 1.2 to 1.5Vdc, the above is not usually attempted for that reason.
If I had a 24Vdc power supply and an LM317 and a 2k trim pot , I could have them all running in no time I could dial up the voltage
until they were all bright enough, shut off the power, measure the position of the trimpot and then replace it with fixed resistors.
Speaking of resistors, I don't see anything in the above about current limiting resistors or their value.