Build Your Own Arcade Controls Forum
Main => Main Forum => Topic started by: krick on November 30, 2008, 02:47:40 pm
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Say that I had a 4-slot coin door with 4 incandescent light bulbs.
If I wanted to replace all the bulbs with 5v LEDs, and then power them off a USB port using one of these cables...
http://groovygamegear.com/webstore/index.php?main_page=product_info&products_id=299
...how do I need to wire them (parallel, I assume) and what sort of resistor(s) are needed?
Also, does anyone sell pre-made 5v LED wedge lamp replacements, or do I need to roll my own?
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For the LEDs, but the cluster ones from Happ (cluster has 3 leds instead of a single). I believe Divemaster sells them. They have a built in resistor. Not a lot of the wedge ones have built in resistors and they will die rather quickly without it.
I think tapping into the USB is a mistake, but people do it. Wire them in parallel and the USB bus "should" have enough current to power all 4.
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Personally, I'd just tap off the 12v line in my power supply, but I know of someone who has a MAME cab based off a laptop. So powering off the USB is the only way to go unless they want to get a separate "wall wart" just for the coin door lights. I'm not sure what they're doing about a marquee either, come to think of it.
Frankly, I'd never try to power a cab off a laptop.
EDIT:
I think these are the HAPP lights you're referring to...
http://www.happcontrols.com/lighting/915wb61w.htm
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Tapping off the 12v power on your power supply is fine for normal coin door bulbs, but for LEDs you would want to use 5v. 12v would pop the leds.
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USB ports are theoretically rated to supply 5v at 500mA, which is enough current to run up to 25 normal LEDs at 20mA each. So USB power should be sufficient for a handful of LEDs. For example, JPACs run on 5v USB and look how many LEDs they support (5 or more), in addition to their video amp and keyboard interface functions.
Using 12v for LEDs is fine, but the wiring is a little trickier. Instead of wiring them all as single LEDs in parallel, you should wire them into series-wired arrays of three or four or five LEDs, with each LED-array wired in parallel. each array will need just one limiting resistor.
Look below for a great LED matrix calculator. this tool will tell you how to design your LED matrix and what limiting resistor to use depending upon your type of LEDs, current source and other specs. It will even draw a circuit diagram for you:
http://led.linear1.org/led.wiz (http://led.linear1.org/led.wiz)
For example, I could make an LED matrix using four red LEDs rated at 2.5v/20mA, wired in series behind a single 27ohm 1/2W resistor and run off the 12v rail. Total power draw would be under 100mA, well within safe range. You could then run four of these arrays in parallel from the same 12v rail, for a total of 16 LEDs with a 'safe' power draw of 400mA.
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Tapping off the 12v power on your power supply is fine for normal coin door bulbs, but for LEDs you would want to use 5v. 12v would pop the leds.
Just wanted to echo pretty much what Zebidee said.
It depends on what rating the LEDs are. The ones krick linked to are either 6v or 12v, you would have to use a 12v source for both bulbs but you would have to use resistor(s) to drop the voltage to 6v.
A 12v source is also fine to use for '5v' LEDs if its all you have availaible, but once again you would need to drop the voltage to 5v (or ~3.5v or whatever).
AFAIK each 12v lead from a typical supply guarantees 18A without triggering the current limit. So theoretically you could connect over 1500 (3.5v 25mA) LEDs in parallel to a 12v whilst drawing 12.5A
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Personally, I'd just tap off the 12v line in my power supply, but I know of someone who has a MAME cab based off a laptop. So powering off the USB is the only way to go unless they want to get a separate "wall wart" just for the coin door lights. I'm not sure what they're doing about a marquee either, come to think of it.
Frankly, I'd never try to power a cab off a laptop.
EDIT:
I think these are the HAPP lights you're referring to...
http://www.happcontrols.com/lighting/915wb61w.htm
Those are them. As you can see they come in 6v or 12v variants with the built in resistor and a variety of colors.
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Tapping off the 12v power on your power supply is fine for normal coin door bulbs, but for LEDs you would want to use 5v. 12v would pop the leds.
I'd use 12v LEDs when tapping the 12v line, of course.
In fact, here's my J-PAC mod to make it work...
http://mame.3feetunder.com/jpacmod/