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Everything You Always Wanted To Know About LEDs But Were Afraid To Ask
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 Posted: Mon Jul 1st, 2019 03:23 pm
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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




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 Posted: Mon Jul 1st, 2019 03:42 pm
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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




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 Posted: Mon Jul 1st, 2019 09:14 pm
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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.





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 Posted: Mon Jul 1st, 2019 09:27 pm
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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.




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 Posted: Tue Jul 2nd, 2019 09:35 pm
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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.




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 Posted: Wed Jul 3rd, 2019 08:24 am
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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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