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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?



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


Eric T
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Thank you.

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.


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.


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.


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.


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


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


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.



corv8
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2foot6 wrote: I think the issue is the LED is reversed.

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


Peter,

Makes sense.

Seems I thought too complicated.

Gerold


tebee
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If you are using normal layout power for your LEDs,
remember that most transformers for model railroad use supply unsmoothed DC,
you may see a flicker in the LED lights with this.


Either use a smoothing capacitor,
or one of the power supplies specifically made for LED lights.


Tom


Helmut
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Curent going from 0 to 100% 50 or 60 times per second results in a flicker no human eye is able to follow.

Only when other light sources driven by AC are present, a sort of stroboscopic effect may occur.



corv8
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Unfortunately DCC decoders generate a similar effect when dimming lights.

When using a value below 80 or so (out of 255) you will see a distinctive flickering.

(no idea with which frequency this flickering will occur)

A plain bulb wouldn't show this effect.

One of the pitfalls of DCC.


Helmut
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The dimming frequency is dependent of the decoder's make and sometimes is considerably less than 50Hz.

Continuous dimming is a relic from the times when bulbs were used,
and due to the filament's inertia, can be done at a rather low rate.

Today dimming mainly makes only sense for high/low beam headlight control.

So when output-dimming is off, no LED will flicker whatsoever.

It may be seen, however, when you have more than one protocol active at the same time,
e.g. DCC and Märklin-Motorola and the lights are connected single-ended to one pickup.

This is an effect generated by the CU's timing when sending the telegrams out.


corv8
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Helmut,

My experience mainly relates to Lenz decoders, which I use for all non sound locomotives.
Other decoders may act differently.

However, I use the dimming feature on some locomotives where I feel the light emitted by the usual LEDs is to bright....
like on an old logging loco. 

A problem with Lenz is that you can only dim once....
you enter a value less than 255 for constant dimming,
but you then no longer have the option to dim the headlight once more when stopping the train.
 
In this case, I connect the function leads C + D to the front + back lights, and enter a lower value for them.
So I may operate the loco with F0 at value "150" when underway, and switch to F2, value "80" when I stop her.



Last edited on Sun Jul 7th, 2019 12:21 pm by corv8


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