What resistor should I get for flashing LEDs

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Psychochook
 
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What resistor should I get for flashing LEDs

Post by Psychochook »

Hi,

I am looking at a project that will involve me wiring up the Diffused 5mm flashing RGB LED to a 9 volt battery. I am looking to get a switch with two 'On' options, with one On activating the slow flashing LED (Diffused 5mm Slow Fade Flashing RGB LED - 10 pack ) and the other On activating the fast flashing LED. I want to connect the LEDs to a 9 volt battery.

How can I work out what strength resistor I need to use with these LEDs?

Thanks

Simon

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adafruit_support_bill
 
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Re: What resistor should I get for flashing LEDs

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Psychochook
 
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Re: What resistor should I get for flashing LEDs

Post by Psychochook »

Hi,

Thanks for the link, and thanks for the tutorial. It was certainly helpful.

I have a couple of questions from the tutorial that I hope someone can help me with.

1 - For my first project I am trying to give a skull that my wife has created red glowing eyes. I was going to get 2 red leds, a switch and a power supply. Can you clarify the following with regards to calculating the Forward voltage. If I assume that the leds use 2 volts, and I am attaching them to a 5 volt power supply, do I calculate the Forward voltage as 1 volt (5v-(2v+2v)), or do I consider both leds and only one user of power which would calculate the Forward voltage as 3 volts (5 v - 2v)?

2 - In the diagram used when demonstrating the power usage (eg - page 20) it shows the led appearing before the resistor. When I am wiring up my circuit I would have thought that the resister would sit between the power supply and the LED. Does it matter where on the circuit the resistor is placed?

3 - If I want to reduce the brightness of the LEDs, there are two ways to do that. Reduce the volts or increase the resistance. Let's assume that I have the two LEDs and they use 2 volts each. I connect them on one circuit to a 3 volt battery. Does that mean that they will evenly distribute the volts between the two of them, or will the first one on the circuit use 2 volts and the second one will have only one volt available to it?

Sorry if these seem like stupid questions, but it would help remove some confusion for me.

Thanks in advance for any help.

Simon

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adafruit_support_bill
 
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Re: What resistor should I get for flashing LEDs

Post by adafruit_support_bill »

1 - If you are wiring the leds in series, you need to add their forward voltages. So, for 2 leds@2v, the combined forward voltage is 4v.

2 - It doesn't matter where the resistor is, as long as it is in series. You could put it between the leds if you like.

3 - We use the voltage and resistance to indirectly control the important parameter: the current. There can be small variations in the forward voltage of 2 leds, even from the same manufacturer. But if you wire them in series, the laws of physics are on your side and they will both always see the same current.

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