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Author Topic: A quick question on wiring leds  (Read 609 times)

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Offline TrevL

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A quick question on wiring leds
« on: December 10, 2018, 10:53:04 AM »
Does it matter which leg of the LED you attach the resistor to?
Just wiring up my mimic and have soldered the resistor to the short  (-ve) leg of about 30 LEDs, but I've just seen elsewhere the resistor attached to the long (+ve) leg,, now I've got doubt in my mind.
Cheers, Trev.


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Offline Steven B

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Re: A quick question on wiring leds
« Reply #1 on: December 10, 2018, 11:21:41 AM »
It doesn't matter which leg the LED goes on.

I would always recommend one resistor per lit LED though.

Steven B.

Offline TrevL

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Re: A quick question on wiring leds
« Reply #2 on: December 10, 2018, 11:30:51 AM »
Thanks Steven, that'll save having to de-solder them all, and yes, I have one resistor per LED.
 :thankyousign:
Cheers, Trev.


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Offline Torchy85

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Re: A quick question on wiring leds
« Reply #3 on: December 11, 2018, 09:31:39 AM »
One thing I would say is just solder resister to the same leg  +ve or -ve on all the LED's. No real reason but it will  possibly look a little neater that way  ;) and may help wiring if you add more LED's  :)
If at first you don't succeed, get somebody else to do it :)

Offline TrevL

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Re: A quick question on wiring leds
« Reply #4 on: January 02, 2019, 05:22:43 PM »
I realise this is basic electronics, but as I don't have basic electronics in my knowledge bank,  would some kind soul please tell me the value of the resistor?



Also, as it is, it is too bright for the purposes it's intended, and as I have more of these resistors, should I add another one in parallel or in series please?
 
Would anyone care to recommend an on-line resource where I can learn the basics please?
Cheers, Trev.


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Online themadhippy

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Re: A quick question on wiring leds
« Reply #5 on: January 02, 2019, 05:48:21 PM »
That resistor is 820 ohm 5% tolerance,to reduce brightness add more resistors in series,if your other resistors are the same value 2 in series will give you 1640 ohms, if thats  too dim try two in parallel (410 ohms)  with 1 in series ,that will give you 1230 ohms
« Last Edit: January 02, 2019, 05:50:47 PM by themadhippy »

Offline ntpntpntp

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Re: A quick question on wiring leds
« Reply #6 on: January 02, 2019, 06:34:49 PM »
There are plenty of online resistor code calculator / translators, here's one:

https://www.digikey.co.uk/en/resources/conversion-calculators/conversion-calculator-resistor-color-code-4-band

... and here it is confirming what @themadhippy  wrote:


Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline ntpntpntp

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Re: A quick question on wiring leds
« Reply #7 on: January 02, 2019, 06:56:31 PM »
@TrevL   What voltage are you powering the LED with?    I'd say 820 ohms is a little low for the typical 12V-15V , a 1K (1000) ohms resistor is more typical for that sort of voltage and a modern LED, and go even higher if you want to reduce the brightness for particular applications. 

I quite often use something more like 1500 ohms for standard LEDs at 15V, and for the tiny SMD LEDs somewhere between 2500 and 4000 ohms.
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline TrevL

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Re: A quick question on wiring leds
« Reply #8 on: January 02, 2019, 07:18:51 PM »
Thank you both @ntpntpntp @themadhippy.
The LED in question is part of a kit of sixteen which goes with point position indicator PCB for eight points. It works with a 12vdc power supply and detects the pulse from the CDU which the lights one of two LEDs on the mimic.  It works very well, the only problem being the LEDs, they are all green, just that some of them are almost twice as bright as the others, but visually they all look like the one in the photo.  This of course looks not too good on the mimic with some lights just right, and others really bright in comparison.
Cheers, Trev.


Time flys like an arrow, fruit flies like a banana!

Offline ntpntpntp

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Re: A quick question on wiring leds
« Reply #9 on: January 02, 2019, 07:34:38 PM »
...the LEDs, they are all green, just that some of them are almost twice as bright as the others, but visually they all look like the one in the photo. 


What happens if you swap a bright one with a dim one? 

If the dim one is still dim in the new circuit then it would probably indicate a variation in the type of LEDs you've been supplied with.

If the dim one becomes bright (and v.v) then it would indicate a problem with the circuitry, either having a different resistor or different voltage flowing through it?


In terms of online resources to "learn the basics", there are literally 100s of different peoples' attempts to write about the subject, and it depends how "basic" you need it to be? Some succeed in explaining things better than others, so try a few alternatives that google throws up in response to a search such as "LED basics for model railways" if that's what you particularly want?

Here's just one random example which seemed better than some of the others I looked at:
http://www.009.cd2.com/members/how_to/leds.htm
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline TrevL

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Re: A quick question on wiring leds
« Reply #10 on: January 02, 2019, 07:42:14 PM »
I'll go check, will get back to you later.
Cheers, Trev.


Time flys like an arrow, fruit flies like a banana!

Offline TrevL

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Re: A quick question on wiring leds
« Reply #11 on: January 02, 2019, 08:27:10 PM »
Right then, after looking carefully, I've discovered I have two different shades of green, just tested them all with the same 12vdc supply and there is quite a marked difference when lit, and very little difference when unlit.  Have tried two resistors, and it still needs dimming more, I'll try again with three or four, then I'll know what value I need to get.  The really bright one is on the right.


« Last Edit: January 02, 2019, 08:29:13 PM by TrevL »
Cheers, Trev.


Time flys like an arrow, fruit flies like a banana!

Offline Malc

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Re: A quick question on wiring leds
« Reply #12 on: January 02, 2019, 08:51:22 PM »
If you are interested in basic electronics, MERG does a free book aimed at electronics for modellers. See https://www.merg.org.uk/ebook.php
I'm not sure if life is passing me by, or trying to run me over.

Offline ntpntpntp

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Re: A quick question on wiring leds
« Reply #13 on: January 02, 2019, 10:36:39 PM »
I've discovered I have two different shades of green, just tested them all with the same 12vdc supply and there is quite a marked difference when lit, and very little difference when unlit.

Did they all come with the position indicator kit/unit or did you buy them separately?    LEDs aren't expensive, I'd be tempted to put that lot to one side for some other use, and just order yourself a new batch. 
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline Madann01

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Re: A quick question on wiring leds
« Reply #14 on: January 02, 2019, 10:53:37 PM »
If you are interested in basic electronics, MERG does a free book aimed at electronics for modellers. See https://www.merg.org.uk/ebook.php



Have just had a quick look at this book download and it seams very concise and put together very well by MERG  :thumbsup:
A usefull resource tool

 

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