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Everything You Always Wanted To Know About LEDs But Were Afraid To Ask
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 Posted: Sat Jun 29th, 2019 01:56 pm
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Eric T
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I read that I'm supposed to use 1000 Ohm quarter-Watt resistors, for the 12-14 Volts my layout uses.

Is that what you all use?

Also, can I simplify the installation process, by installing a single resistor on the blue wire,
instead of putting resistors on both the white and yellow wires?

Finally, does it matter which end of a resistor is positive or negative?



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 Posted: Sat Jun 29th, 2019 11:32 pm
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2foot6
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Hello Eric,

I use resistors from 800 Ohm to 3K Ohm,
depending on the brightness of the individual LED,
and the brightness I require.

If there is too much resistance, the LED will simply not work.

Yes you can make wiring easier.

You only need to use one resistor on any of the wires of the LED,
and resistors do not have a positive or negative wire,
they are just a resistance in a circuit.

Not polarity sensitive...They can be wired in either way.

:apl:

........Peter




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 Posted: Sun Jun 30th, 2019 01:26 am
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Eric T
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Thank you.

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 Posted: Sun Jun 30th, 2019 08:36 am
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slateworks
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Eric,

you may find this resistor calculator useful in deciding on the values you need,
according to how many LEDs you have and how they are set up, in series or parallel.

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

It will help you work out the minimum value for "safe" operation and, as Peter has suggested,
you can move up from there in deciding the brightness level you want.




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 Posted: Sun Jun 30th, 2019 09:45 am
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Si.
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Some helpful diagrams.  :brill:


How to recognize which way round to connect LEDs,
Which are 'direction-important' components,
Having both a  '+ Anode'  &  '- Cathode'.

And connecting the non-directional 'current-limiting resistor'.































:!::!: :!: :!: :!:



Si.




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 Posted: Sun Jun 30th, 2019 10:05 am
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Si.
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How to recognise the standard 'colour band codes' on most resistors.  :brill:

And calculate what value of resistor is needed for your LED types.  L:








Resistor value in Ohms = VS 'Supply-Voltage' ... MINUS - VF 'Forward LED Voltage' ...

... DIVIDED by the maximum, or desired, LED current in Amps, ie. say 20 mA = 0.020 Amps.

The answer is the 'current limiting resistor' value in Ohms, which can be a 'nearest value'.





An example of 'chaining' LEDs using different resistor values & different Voltages.






:!: :!: :!: :!: :!:



Si.




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 Posted: Sun Jun 30th, 2019 10:21 am
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Si.
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Interesting chart, showing 8 different colour LEDs, right across the spectrum ...  :brill:

... including the invisible-light of both the Infra-Red & Ultra-Violet LEDs ...

... Infra-Red, Red, Orange, Green, Yellow, Blue, White, & Ultra-Violet.





You can see that all the different colours of LED, have different VF Forward-Voltages.





Some calculated 'standard resistor values' ...

... For series resistors R ... with different supply Voltages Vs ... & LED colours.

Operating current figures & the LEDs 'forward Voltage drops' are not show.



Operating current in mA (milliAmps) can be varied, up to the maximum allowed, according to taste.

The various 'forward Voltage drops', as we can see in the graph ^^ above, vary with LED colour.





:!: :!: :!: :!: :!:



Si.




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 Posted: Sun Jun 30th, 2019 10:28 am
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2foot6
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An interesting find on an auction site,
was a dealer selling resistors from 0 Ohms to very high in the Meg-Ohms.

Why would you buy a zero Ohm resistor, when a piece of wire is the same thing ?
Should have bought one to see how they marked the resistor ... Three black bands ? ... :dope:

......Peter




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 Posted: Sun Jun 30th, 2019 11:32 am
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corv8
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Si. wrote:





Si,

What is the negative aspect when the resistor is connected,
like shown at the RH diagram ?

I have never cared where to put the resistor,
normally I decide where it is easier regarding routing the wires. 

Haven't noticed any difference.

 
Gerold




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 Posted: Sun Jun 30th, 2019 11:44 am
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2foot6
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I think the issue is the LED is reversed.

It will make no difference whatsoever where the resistor is placed in the circuit.

......Peter.





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