Is this circuit possible? And what resistor should I use?

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Discussion Overview

The discussion revolves around the feasibility of a circuit design involving 6 white LEDs powered by a 9V battery. Participants explore the appropriate resistor values needed to achieve desired brightness levels while addressing concerns about power supply and circuit configuration.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant questions the possibility of lighting 6 LEDs with a 9V battery and seeks advice on the necessary resistor value.
  • Another participant suggests starting with a 1k resistor and adjusting for brightness.
  • A technical explanation is provided regarding the forward voltage drop of white LEDs and calculations for resistor values based on desired current levels.
  • Participants discuss the option of wiring LEDs in series pairs to reduce total current and increase battery life.
  • Jamie inquires about using normal wire instead of jumper cables for the breadboard setup.

Areas of Agreement / Disagreement

Participants generally agree on the feasibility of the circuit and provide various resistor values, but there is no consensus on a single optimal solution. The discussion remains open regarding the best approach to achieve the desired LED brightness.

Contextual Notes

Some calculations depend on specific assumptions about LED characteristics and desired brightness levels, which may vary. The discussion does not resolve the exact configurations or resistor values needed for optimal performance.

Who May Find This Useful

Individuals interested in basic electronics, circuit design, or those seeking guidance on LED configurations and resistor calculations may find this discussion beneficial.

JJM596
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Hi all,
I am a new member here.

I am quite new to making circuits,etc. and have decided to make something easy-ish on a breadboard. I have included a diagram of what I am planning to make. I am using 6x white
LEDs and a 9v battery. I was wondering what resistor I should use for
this? Also, is this even possible? Do I have enough power to light up 6 LEDs not full power
, as I know i don't have enough power for that, but even just a little bit bright? Would really appreciate
any help on this. apologies for bad grammar, am in a rush!

Thanks, Jamie
Ireland
 

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Hey there Jamie
welcome to PF

1k resistors ( as currently shown) would be OK as a starting point, then increase or decrease a little to get the brightness you want

Make sure you have the LED's the right way around :smile:Dave
 
White LEDs drop a forward voltage of about 3.3V.

Each LED will have (9V – 3.3V) / 1kR = 5.7 mA. I would have expected Ifwd to be closer to a typical 20 mA.
For 20 mA you would use R = (9V – 3.3V) / 20 mA = 285 ohms, use standard value 270R.
Total current will be 6 chains * 21.1 mA = 126.6 mA.

You can save energy by wiring LEDs in series pairs. Then for 20 mA LED current you need a series;
R = (9V – 3.3V – 3.3V) / 20mA = 120 ohms, a standard value.
Total current will be I = 3 chains * 20 mA = 60 mA.
So the battery should last twice as long.
 
Thank you for a quick reply:) This helps a lot!
One more question though, can I use normal wire instead of using breadboard jumper cable wires?
I have "normal" wire so if I could use it it would save having to buy the jumper cables.

Thanks again,Jamie
 
yes.
 

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