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Author Topic: 3mm round LEDs  (Read 459 times)

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Offline springwood

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3mm round LEDs
« on: March 24, 2019, 02:36:53 PM »
I'm looking to use some different coloured 3mm round LEDs (for status indicators on my control panel) and have purchased a load of them, plus other electrical bits and bobs, from a really good supplier called Bright Components Ltd, based in Northampton. (website is www.bright-components.co.uk).

The green ones I have bought are:  http://bright-components.co.uk/epages/950004269.sf/en_GB/?ObjectPath=/Shops/950004269/Products/greendiffused3mm50

Just set one up in a simple 12v dc switched circuit - see attached diagram - but immediately find that the bulb is really (almost blindingly!) bright. What would I need to do to dim the brightness down? I think I would need a haeavier duty resistor??

As usual, pointers/suggestions welcomed. Thank you.
Robin

Offline ntpntpntp

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Re: 3mm round LEDs
« Reply #1 on: March 24, 2019, 03:28:29 PM »
You don't need "heavier duty" (higher wattage) but you need higher resistance. You need at least a 1k ohm resistor, and be prepared to go higher if you want less brightness.  1k2 or 1k5 for example.

20mA is a lot for a modern 3mm LED unless it's a "high brightness" or "ultra bright" type.  You can go lower with the current - 15mA or even 10mA.  The tiny SMD LEDs I've used for models are more like 2-3mA.

Get yourself a set of mixed resistors and experiment to see what suits you best.  Also remember the forward voltage of different colours of LED are different so you might find you need slightly different resistor values for each colour in order to perceive the same level of brightness.
« Last Edit: March 24, 2019, 03:37:57 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Online JanW

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Re: 3mm round LEDs
« Reply #2 on: March 24, 2019, 03:32:43 PM »
Do you have any resistors to test with?
I have used resistors up to 10kOhm to tame bright LED's.
If not you can add 1kOhm resistors in series until you find the desired brightness and then you can order the right resistors.

Jan

p.s. while I was typing ntp has given a similar answer...

Online Delboy

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She who must be obeyed says I am spending too much time on this forum. I love her dearly but what does she know?

Offline Gary Burcombe

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Re: 3mm round LEDs
« Reply #4 on: March 24, 2019, 03:51:35 PM »
I have built a couple of mimic boards / control panels and powered the LEDs from old mobile phone chargers.  They put out about 5v DC and I did the maths to work out the resistances to achieve the recommended current requirements of the LEDs.  They were still too bright, so I did exactly what has been suggested already and I now use 2k2 for green and 470r for the amber.  This lowering of the current also increases the life of the LEDs too, bonus!

Online Paul-H

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Re: 3mm round LEDs
« Reply #5 on: March 24, 2019, 03:56:31 PM »
You don't say in your OP but did you use any resistors, I assume you must as 12v would normally blow a 2v LED instantly

What value are you using now.

This is were I find my old resistance box comes into it's own, just adjust the knobs until the brightness is right then read of the value, best 50p I ever spent at a boot sale.

Paul
« Last Edit: March 25, 2019, 09:05:59 AM by Paul-H »
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Online Delboy

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Re: 3mm round LEDs
« Reply #6 on: March 24, 2019, 05:01:25 PM »


This is were I find my old resistance box comes into it's own, just adjust the knobs until the brightness is right then read of the value, best 50p I ever spent at a boot sale.

Paul
Hi Paul,
Is this what could purchased to test brightness?
She who must be obeyed says I am spending too much time on this forum. I love her dearly but what does she know?

Offline ntpntpntp

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Re: 3mm round LEDs
« Reply #7 on: March 24, 2019, 05:33:52 PM »
@Delboy

This kind of thing (this is just a cheapo box but good enough for our sort of use).
https://www.ebay.co.uk/itm/Lehre-Resistance-Widerstand-Box-Instrument-Variabel-Resistor-Precision-Variable/143163612440



Always start high and work down to find the minimum resistance which does what you want.
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Online dannyboy

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Re: 3mm round LEDs
« Reply #8 on: March 24, 2019, 05:49:27 PM »
@ntpntpntp  Thanks for that link. I did an ebay search and came up with many similar things. I presume you just connect the led leads to the red and black at the bottom, start with, say, 1 x 1000 and then work down? When you find the resistance that gives the required result, go and buy some resistors that correspond to the result on the box?   ???. I have learnt a lot regarding 'miniature' electrics from members of the forum such as yourself, but am still trying to learn more.   :thankyousign:
David.
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Online themadhippy

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Re: 3mm round LEDs
« Reply #9 on: March 24, 2019, 05:53:58 PM »
Quote
I presume you just connect the led leads to the red and black at the bottom
No,it goes in series with the LED,so power + to the red terminal,led + to the black terminal and power - to the LED -

Online dannyboy

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Re: 3mm round LEDs
« Reply #10 on: March 24, 2019, 06:09:17 PM »
When you think about how a resistor is wired up to a LED your answer is obvious. Why didn't I think of that?  :doh: . As I said, I am still learning.  :)
David.
I used to be indecisive - now I'm not - I don't think.
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Online class37025

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Re: 3mm round LEDs
« Reply #11 on: March 24, 2019, 06:30:57 PM »
just followed the link and added one to my basket.

for that price looks like a great investment.
typed by fur box mechanic - dictated by brain on a chain

Offline ntpntpntp

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Re: 3mm round LEDs
« Reply #12 on: March 24, 2019, 07:21:58 PM »
just followed the link and added one to my basket.

for that price looks like a great investment.

Yeah I ordered one.  I have plenty of resistors all sorted by decades, but occasionally I think this little box will come in handy rather than fiddling around choosing resistors and clipping them in with croc-clips to try each one.
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline springwood

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Re: 3mm round LEDs
« Reply #13 on: March 25, 2019, 08:46:02 AM »
They were still too bright, so I did exactly what has been suggested already and I now use 2k2 for green and 470r for the amber.  This lowering of the current also increases the life of the LEDs too, bonus!

I emailed the shop about the brightness of the green LEDs, asking for advice on resistors. Their response was 'Yes, these are an efficient and bright LED. It's hard for me to recommend a specific resistor as every customer has a different idea of 'normal' brightness.  Maybe 10k is worth trying?

Do you reckon that's worth a go, but get some others at the same time as well?

Online Bealman

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Re: 3mm round LEDs
« Reply #14 on: March 25, 2019, 10:05:31 AM »
A resistance substitution box is not a new idea, but is a very is a very useful bit of kit in a situation like this.
Vision over visibility. Bono, U2.

 

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