Electronics

nige · Joined: 08 Aug 2006 Posts: 4

Hi all, I wonder if you could help me. I want to light the interior of my model train coaches. I can buy ready made items like this:- http://www.massoth.com/index2.html - (look under products & services - lighting electronics) but the cost is prohibitive. I do not know much about electronics but can use a soldering iron! The unit would be fed with 0 to 24 volts. Is it possible to use 6 or 12 volt bulbs without blowing them thus giving a constant glow? Any help you can give me would be much appreciated including suppliers in the UK.
Thanks,
nige

neon · Joined: 25 Feb 2006 Posts: 594

LEDare the answer low cost. Efficiency easy to implement. WE need to know how many LEDs are needed. I assume 10 to begin wiht. When you buy LEDs you can choose color and buy superbrights max $2 each then you will need a current souce LM117 $.75 since your volts are 0 to 24v. I can get some design for you at no cost provided i know exactly what you want. For now buy a LED superbright and use 12v and a 1k resistor in series and that will tell you if good enough. Change the 1k to 0.5k and that will make it brighter. YOU MUST KNOW what you want. bulbs are good too but current huggers too.The best that i know of is 222 and draws 300ma each.

nige · Joined: 08 Aug 2006 Posts: 4

Hi Neon, thanks for your reply. LED's would be better due to low ampage and lifespan, I would need a maximum of 4 LED/Bulbs per unit. You have lost me on current source and resistors, i'm afraid I know nothing about them. The light does not have to be too bright, just enough to light the interior.
I am thinking that the unit would work out something like wires to a switch then to a voltage regulator or similar then to LED's.
Please correct me if I am wrong. Also would the LED's be better in a holder or soldered to a board?
Thanks, nige

neon · Joined: 25 Feb 2006 Posts: 594

crush course on LEDS are diodes and each drops about 2v to 4v each and requires .01 to .05 amps each. depends of what you buy this is just the rule of the game. now for 12v you may put try 4 LEDS one after the other is called serial connection and to limit the current so that they don't go on vacation you must add a resistor again in series to limit the current to an acceptable level. If you want to do it buy the leds and connect 4 one after the other in [series] with the resistor to 12v the resistor now must be calculated as diodes voltage drops 2.5+2.5+2.5+2.5=10v 12-10=2 now 2v remaining is what you need to limit the current to say .015 amps so 2/.015=130 ohms this rule apply to 1,2,3or4 leds 5 leds will not work because it will exceed the 12 v source.need further help?the LEDS can be wired easely with wire wrap.Boards will not work too easy because of the remote wireing. SOLDER IS GOOD glue thenm down with RTV to hold

nige · Joined: 08 Aug 2006 Posts: 4

Hi neon, how would I regulate the voltage because it is going to fluctuate between 0 and 24 volts?
nige

neon · Joined: 25 Feb 2006 Posts: 594

Well you cannot. 0 v is absolute no power available to do nothing so what can you do. well lets put some real number down. min voltage to function and that means one led only because 4 in series to see light you need min 8 v. lets try one we must use current regulator for each lm117 cost $.50 each lets limit the current to 50 ma max so put a 24 oms .25win series with the lamp and regulator. if you don't know what i am saying then pass along e-mail and i will send you schematic instructions. that is the best that i can do. take care.

nige · Joined: 08 Aug 2006 Posts: 4

neon, PM sent. Nige

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