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LED circuits - Help and advice.


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Hi guys, first post here and it's good to be here. I have seen some awesome models in my short time here and some good convocation. 

Anyway, I am just getting back into modelling after close to a 25 year gap. I have bought all the required tools, a good airbrush and compressor ETC and look forward to getting started as an adult ūüėÄ

 

Around 15 years ago I started the Revell QM2, drilled out the hull etc, but after making a mistake with the painting it's been put onhold until very recently. 

I've since completely lightblocked the hull with black fabric paint in preparation for LED's and fiber optics. 

 

Here is where my problem lies, and the reason for this post. I'm a complete noob when it comes to electric and the such though have been learning. 

I see (using a calculator) that with a 5v power supply I can power my strawhat orange LED's, 20 or so of them, with 330ohm resistors - 7 I think it said.

Now, how do I go about adding another circuit of another set of SMD's, say 22 or so + red and green navigation? 

Ho do I go about adding them all together - added resistors ETC. 

 

I'd be most greatful if someone would be willing to help me calculate the circuit I require so I can learn and progress with my model as I'm stuck at the moment until I get the hull lights/lights planned and working. 

 

Have a good day all 

 

Regards

Edited by Davidrebolton
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What figures did you use to get to 330ohm? (Foreword voltage and current of the LEDs)

 

Your red & green LEDs could be connected in parallel to your 5v supply along with another separate current limiting resistor. Or you could add them in parallel to your existing LEDs with the same 330ohm resistor.

 

 

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36 minutes ago, Cheshiretaurus said:

What figures did you use to get to 330ohm? (Foreword voltage and current of the LEDs)

 

Your red & green LEDs could be connected in parallel to your 5v supply along with another separate current limiting resistor. Or you could add them in parallel to your existing LEDs with the same 330ohm resistor.

 

 

Yes they were the figures I used. 

 

So basically with a constant 5v I can power all of these lights using the 330's? 

How would I go about calulating how many additional resistors I may need  for the other circuits? 

Thank you, I'm eager to learn

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No, you can't. The human eye perceives different colors at different intensities even if in theory the light output is the same. You need to separate them by colors and do each color depending on the effect you want to achieve. 

Also because of Murphy's law I never group more than two LEDs on the same resistor. If the connection breaks on the resistor you end up with 1-2 LEDs that don't work, but if you have all of them on the same resistor then none will work.

Buy (or order) a bunch of different value resistors and test for light intensity before committing to gluing everything in place.

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So you want to do something like this for your orange LEDs?   I've not included the red & green LEDs just yet.

 

CdMx3lj.png

 

 

 

 

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6 minutes ago, bmwh548 said:

No, you can't. The human eye perceives different colors at different intensities even if in theory the light output is the same. You need to separate them by colors and do each color depending on the effect you want to achieve. 

Also because of Murphy's law I never group more than two LEDs on the same resistor. If the connection breaks on the resistor you end up with 1-2 LEDs that don't work, but if you have all of them on the same resistor then none will work.

Buy (or order) a bunch of different value resistors and test for light intensity before committing to gluing everything in place.

Thank you!! I shall have to order a selection and just test + a 5v charger or the such. I see we can buy a high-amp voltage reducer, something which I see someone else has done and embedded it into the stand - nice and small - I may do the same for the power supply. 

 

So I can just add other circuits to the base hull lighting circuit shall we say? 

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2 minutes ago, Cheshiretaurus said:

So you want to do something like this for your orange LEDs?   I've not included the red & green LEDs just yet.

 

CdMx3lj.png

 

 

 

 

Aweosme thank you, yes the orange. Still not completely sure how many I'll use but close to that number. 

Its a start for me. I've watched so many videos, read loads of explanations but am just still stuck lol 

 

I'm also planning to add an RGB disco type LED - only the one :)

 

 

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1 minute ago, Davidrebolton said:

 

 

I'm also planning to add an RGB disco type LED - only the one :)

 

 

Now it gets complex as you will need a controller circuit for that!

 

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4 minutes ago, Cheshiretaurus said:

Now it gets complex as you will need a controller circuit for that 

I see. 

 

All in all I want the orange in the bottom, the SMD's along along hull, navigation lights, blue LEDs 5 or 6 + the disco light. 

This is everything I want to try and install. 

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Not necessarily, there's LEDs with the controller integrated. Just be very careful wiring them, most of the controllers don't have a reverse voltage protection and it'll burn instantaneously.

 

You can add as many circuits as you wish (provided you stay in the power supply's limits, but that shouldn't be an issue).

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2 options for adding the red & green :- 

1dheStD.png

 

you could have them both share the same resistor(still needs to be calculated) or each on their own resistors.

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Thanks guys. I appreciate the quick offerings of help. It does look to be getting confusing now though i'll persivear, I'm desperate to learn. 

Perhaps I would be best starting with the initial oranges with resistors, then add and learn from then on? 

 

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17 minutes ago, dnl42 said:

Perhaps you're already aware of this, but you can use a solderless breadboard to ensure your circuit works exactly as you need, from initial experimentation to final mock-up. 

Thats a good idea, its a good investment to learn more circuits on in the future. 

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39 minutes ago, dnl42 said:

Perhaps you're already aware of this, but you can use a solderless breadboard to ensure your circuit works exactly as you need, from initial experimentation to final mock-up. 

 

19 minutes ago, Cheshiretaurus said:

Thats a good idea, its a good investment to learn more circuits on in the future. 

Yes guys I am aware of them and should buy one for what little they cost. I'll order one with the resistors when I order them. 

Most appreciated guys. 

  • Thanks 1
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Have you thought of using Fibre Optic cable (FO)?

 

This 1:350 ship (Scratch built) has only three 5mm LEDs, two yellow and one Ultra white running off a 9v PP3 battery and 3 resistors. Different strengths of resistors can be easily used to brighten / darken the LEDs to the light luminance strength you want. As mentioned, a breadboard makes this kind of stuff very easy to manipulate.

 

All porthole lights run off of yellow LED 1, yellow LED 2 is stuck in the superstructure for the wheelhouse / superstructure lighting and the ultra white LED is for all outside deck and mast lighting. The actual masts are FO cable with gashes to allow light to leak out where I want it.

 

Each LED feeds a bunck of FO cables cut to length and the ends polished with one of my daughters finger nail thingy boards. Port Nav light has a dab of clear red and starboard a dab of clear green Tamiya paint on the polished ends.

 

This shows the FO mess underneath the hull. The black shape at the bottom right is the heatshrink tube that holds the LED and the FO strands.

 

spacer.png

 

 

spacer.png

 

spacer.png

 

Here you can see the tiny FO cable that depicts the Port navigation light:

 

spacer.png

 

Day shot:

 

spacer.png

 

Night shot:

 

spacer.png

 

If you do a search, there are a fair number of build threads showing ship builds with minimal LEDs using Fibre Optic cable.

 

Hope this is of use to you.

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The maths.

 

As a rule of thumb an LED has 2V across it and needs 10mA for a decent illumination.  In reality the actual voltage varies depending on the colour and can be 3V or so and the current can be up to 30mA, the higher the current the brighter but there is a limit to how much current.

 

But as a general rule 2V and 10mA work well.

 

Take a single LED.

 

If the supply voltage is 5V then you will have 2V across the LED so you need (5-2) 3V across the current limiting resistor.

 

You want the current to be 10mA (0.01A) so using Ohm’s law the resistance needed is Voltage/Current so 3/0.01 = 300 ohms

 

But what if you have multiple LEDs in parallel. Let’s use two as an example.

 

The voltage across the resistor is still 3V.  But the current required is now 20mA because you need 10mA for each LED.  The the resistor needed for two LEDs in parallel is 3/0.02 = 150 ohms.

 

If you want seven LEDs in parallel the current through the resistor is now 70mA.  So the resistor needed is 3/0.07 = 43 ohms.

 

Note resistors come in certain sizes so just puck the one nearest to the calculated value.

 

In your example above, I think the 330 you have been specified is for ONE LED.  If you use a single resistor to drive SEVEN LEDs the current through each LED will be very small, may not be enough to light them at all or if it does they may be very dim.

 

Cheers,

 

Nigel

 

 

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21 hours ago, Murdo said:

Have you thought of using Fibre Optic cable (FO)?

 

This 1:350 ship (Scratch built) has only three 5mm LEDs, two yellow and one Ultra white running off a 9v PP3 battery and 3 resistors. Different strengths of resistors can be easily used to brighten / darken the LEDs to the light luminance strength you want. As mentioned, a breadboard makes this kind of stuff very easy to manipulate.

 

All porthole lights run off of yellow LED 1, yellow LED 2 is stuck in the superstructure for the wheelhouse / superstructure lighting and the ultra white LED is for all outside deck and mast lighting. The actual masts are FO cable with gashes to allow light to leak out where I want it.

 

Each LED feeds a bunck of FO cables cut to length and the ends polished with one of my daughters finger nail thingy boards. Port Nav light has a dab of clear red and starboard a dab of clear green Tamiya paint on the polished ends.

 

This shows the FO mess underneath the hull. The black shape at the bottom right is the heatshrink tube that holds the LED and the FO strands.

 

spacer.png

 

 

spacer.png

 

spacer.png

 

Here you can see the tiny FO cable that depicts the Port navigation light:

 

spacer.png

 

Day shot:

 

spacer.png

 

Night shot:

 

spacer.png

 

If you do a search, there are a fair number of build threads showing ship builds with minimal LEDs using Fibre Optic cable.

 

Hope this is of use to you.

Thanks Murdo, it is helpful and I do also have various thickness fibers ready for tinkering hehe. 

15 hours ago, nheather said:

The maths.

 

As a rule of thumb an LED has 2V across it and needs 10mA for a decent illumination.  In reality the actual voltage varies depending on the colour and can be 3V or so and the current can be up to 30mA, the higher the current the brighter but there is a limit to how much current.

 

But as a general rule 2V and 10mA work well.

 

Take a single LED.

 

If the supply voltage is 5V then you will have 2V across the LED so you need (5-2) 3V across the current limiting resistor.

 

You want the current to be 10mA (0.01A) so using Ohm’s law the resistance needed is Voltage/Current so 3/0.01 = 300 ohms

 

But what if you have multiple LEDs in parallel. Let’s use two as an example.

 

The voltage across the resistor is still 3V.  But the current required is now 20mA because you need 10mA for each LED.  The the resistor needed for two LEDs in parallel is 3/0.02 = 150 ohms.

 

If you want seven LEDs in parallel the current through the resistor is now 70mA.  So the resistor needed is 3/0.07 = 43 ohms.

 

Note resistors come in certain sizes so just puck the one nearest to the calculated value.

 

In your example above, I think the 330 you have been specified is for ONE resistor.  If you use a single resistor to drive SEVEN resistors the current through each LED will be very small, may not be enough to light them at all or if it does they may be very dim.

 

Cheers,

 

Nigel

 

 

Thanks for the explanation Nigel, it's appreciated matey 

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So guys I've just bought a bread board and a big multipack of resistors so I'll ha e everything to start tinkering soon. 

 

I've also found a different disco type light as seen at this link 

https://www.gaugemasterretail.com/magento/train-tech-ttsl10.html

Thing is it needs power between 9v-16v, so I think I'll be purchasing a 9v power source for this project. 

 

Thanks to all for your help, I'll likely be posting again soon for more advice and tips.

 

Take care all ūüĎć

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8 minutes ago, Davidrebolton said:

and I do also have various thickness fibers ready for tinkering hehe. 

 

Be careful, it can become rather addictive. My wife was getting really hacked off with my LED / FO produced light shows.         :rofl:

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Posted (edited)
25 minutes ago, Murdo said:

 

Be careful, it can become rather addictive. My wife was getting really hacked off with my LED / FO produced light shows.         :rofl:

Lol I could imagine. I have many 1/24 cars I want to end up lighting with fibers. Although lots more fiddly I feel it will be easier for me given the few LEDs required haha 

The MRS loves cars so she won't mind the constant tinkering ūüėĀ

Trust me to pick the largest transatlantic liner in the world as my first lighting project lol ūüėÜ

Her hull has been totally light sealed to prevent leaks with many coats of black fabric paint- very thick! And plan to do so throughout the model to ensure light only goes where it should 

 

Your help is appreciated and needed hehe 

 

With thanks 

Edited by Davidrebolton
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Regarding this disco light guys https://www.gaugemasterretail.com/magento/train-tech-ttsl10.html

As I stated it needs between 9v-16v. Am I right in thinking that 9v wouldn't be enough given all the other lights on/in the circuit? 

 

Also I see we can buy step-down power modules, a high amp voltage reducer which can be mounted into the models plinth. 

Would someone be able to link me to one? Perhaps higher than 9v depending on the outcome of the first question. I have looked around before asking though not had much luck as, to be honest, I don't know what I'm looking for lol 

 

Thanks all ūüĎćūüí•

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Its not just the voltage its also how much current the supply can provide. If your disco LED needs 9v to operate then you could run your other LEDs from the same supply  just need a higher value resistor.

 

Add up the current required by all the LEDs and add maybe 50% so your power suppy is not Running at max.

As an example if you have say 30 LEDs at 10mA that is 300mA so you should look for a minimum of 450mA for your power supply.

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14 hours ago, Cheshiretaurus said:

Its not just the voltage its also how much current the supply can provide. If your disco LED needs 9v to operate then you could run your other LEDs from the same supply  just need a higher value resistor.

 

Add up the current required by all the LEDs and add maybe 50% so your power suppy is not Running at max.

As an example if you have say 30 LEDs at 10mA that is 300mA so you should look for a minimum of 450mA for your power supply.

I see. I had found this one https://www.ebay.co.uk/itm/164630867449

But going from what you say I see its only rated at 300mA. Would you be able to point me in the direction of which I require with a link ūü§Ē - if you don't mind.¬†

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The 450mA supply I mentioned was an example, What you actually need would depend on your application. Whats the current of the LEDs you will use have you got a link to them?

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