LED powering question

[mvolke1]

Hey All,

I had this 12 volt adapter kicking around so I tried powering a couple LED buttons with it. The test worked well, but I was wondering if anyone could tell me if this is safe and how many LED buttons I could power with it. Thanks for any help!

[PL1]

I had this 12 volt adapter kicking around so I tried powering a couple LED buttons with it. The test worked well, but I was wondering if anyone could tell me if this is safe and how many LED buttons I could power with it. Thanks for any help!

Depends on the exact LEDs you are planning on using, but the pictured 9v, 450mA adapter should have no problem powering at least 22 average LEDs rated for 12v.

20mA per LED * 22 LEDs = 440mA

If needed, you can probably add a few more LEDs since you're running 12v LEDs on 9v which means the current limiting resistor is a higher value than needed = less current draw.

Before adding more than 22 LEDs be sure to use your multimeter to measure the average current draw of the LEDs.

Each LED added in parallel with the others will draw the same current.

If 20 LEDs draw 360mA (18 mA each), 24 LEDs will draw 432mA. (18 mA each)


Scott

[mvolke1]

I had this 12 volt adapter kicking around so I tried powering a couple LED buttons with it. The test worked well, but I was wondering if anyone could tell me if this is safe and how many LED buttons I could power with it. Thanks for any help!

Depends on the exact LEDs you are planning on using, but the pictured 9v, 450mA adapter should have no problem powering at least 22 average LEDs rated for 12v.

20mA per LED * 22 LEDs = 440mA

If needed, you can probably add a few more LEDs since you're running 12v LEDs on 9v which means the current limiting resistor is a higher value than needed = less current draw.

Before adding more than 22 LEDs be sure to use your multimeter to measure the average current draw of the LEDs.

Each LED added in parallel with the others will draw the same current.

If 20 LEDs draw 360mA (18 mA each), 24 LEDs will draw 432mA. (18 mA each)


Scott

Thanks so much for the reply!

So I should be good with running 14 buttons in total then?

12 would be these: http://www.ebay.com/itm/281100072416?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

2 would be these 100ma @ 5v DC Per button: http://groovygamegear.com/webstore/index.php?main_page=product_info&cPath=73&products_id=295

[PL1]

12 would be these: http://www.ebay.com/itm/281100072416?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

No problems with these.

They have the current limiting resistor inside the LED holder and will light with any voltage from 5v - 12v.

2 would be these 100ma @ 5v DC Per button: http://groovygamegear.com/webstore/index.php?main_page=product_info&cPath=73&products_id=295

Trying to run these on 9v will let the "magic smoke" out of them UNLESS you change the resistor or add another current limiting resistor in series.

You should ask RandyT if he can do one of two things for you:

    1. Swap the built-in resistor for one that will work with 9v.

    2. Tell you the correct resistor (Ohms and Watts) to add in series for it to work with 9v.
        (Ask what resistor to use for 12v while you're at it, since that is a more common LED voltage.  )


Scott

[mvolke1]

Thanks again Scott! What's the magic smoke? Will it burn it out?

[mvolke1]

One more thing, I gave you the wrong button. I got these: http://rover.ebay.com/rover/0/e11400.m1842.l3160/7?euid=3f6a5d3795b74fb69baef79d39083fc7&loc=http%3A%2F%2Fcgi.ebay.com%2Fws%2FeBayISAPI.dll%3FViewItem%26item%3D360296413375%26ssPageName%3DADME%3AL%3AOC%3AUS%3A3160

[PL1]

What's the magic smoke? Will it burn it out?

The joke is that all electronic components contain "magic smoke" -- they stop working when you let it out.   

Applying 9v to an LED/current limiting resistor combination rated for 5v will definitely burn it out unless you add another resistor to drop the extra 4v.

The CDRs have an LED and current limiting resistor (R1) combination rated for 5v.

       5v --- LED -- R1 --- Ground

To safely use 9v, you'll need to add a second current limiting resistor (R2) that drops 4v.

       9v --- LED -- R1 --- R2 --- Ground

           or

       9v --- R2 --- LED -- R1 --- Ground

Either way works.

One more thing, I gave you the wrong button. I got these: http://rover.ebay.com/rover/0/e11400.m1842.l3160/7?euid=3f6a5d3795b74fb69baef79d39083fc7&loc=http%3A%2F%2Fcgi.ebay.com%2Fws%2FeBayISAPI.dll%3FViewItem%26item%3D360296413375%26ssPageName%3DADME%3AL%3AOC%3AUS%3A3160

LEDs in both are rated for 12v -- no problem.   

They probably come from the same factory.   


Scott

[mvolke1]

You're the man.

Do you think another solution would be to buy one more of those green buttons and then just switching out the LED lamps?

[PL1]

Not sure if you are giving up on all rectangular buttons or just looking for different ideas so I'll just throw some options your way and see if there's anything you like.

The translucent round LED buttons come in a variety of colors with matching LEDs. (Avoid yellow button with yellow LED or you get muddy orange )

Rick said here that he will be getting some black rimmed ones soon. (not the sawed-off volcano-wannabes  )

You can print your own inserts like the ones here.



If you want to use rectangular buttons like these or these from Divemaster, the #161 incandescent bulbs they come with have the same wedge-base as the LEDs in the buttons you linked. (confirmed good fit with the low-profiile ones)



Louis Tully is printing custom inserts for the CDRs on his Asteroids Deluxe build here.




Scott

[mvolke1]

Hey Scott,

I didn't want to give up on the square insert coin button. What I was think was maybe switching out the lamp and bulb from another switch rather than wiring up something new.

Do you think I could just switch these parts out?

[PL1]

Disclaimer: I have not worked with the CDRs.

The low-profile rectangular buttons use a straight-pull to release instead of the the twist-to-lock switch-holder/LED-socket used by the round buttons. (or the twist-to-lock low-profile triangular ones)

Based on this pic by Louis Tully, the CDRs appear to have locking lugs of a similar location and size to the round LED buttons, but someone who actually has both would have to verify whether or not you can swap switch-holder/LED-sockets.



The downside if you can swap parts is probably losing brightness and maybe the evenness of the lighting (depending on how wide-angle the LED is) -- I recommend adding the second resistor instead.


Scott

[j1345]

mvolke1:  How did you connect that to the LED buttons?  Can you detail that...  I'm trying to do the same thing.

[mvolke1]

Hey Scott, you're right about the button differences. I emailed randy to see if he has a 12 lamp I could buy and replace. I'd rather do that than trust my skills messing with the existing lamp.

As for wiring, I ran wires from the hot, grouped them together with one of those twisty wire connectors and did the same for the ground. I cut the connector off an old 9v adapter and ran the hot to the hot and the ground to the ground.dies that make sense?

[PL1]

  Didn't think about this earlier, but you could just wire the two CDRs in series to drop 4.5v on each.

This will be the easiest way to wire it all together and keep everything well within the power supply specs.

9v ---- red wire - CDR - black wire ---- red wire - CDR - black wire ---- Ground
      |                                                                                               |
      ------------------------12v round LED button-----------------------
      |                                                                                               |
      ------------------------12v round LED button-----------------------
      |                                                                                               |
      ------------------------12v round LED button-----------------------
      |                                                                                               |
      ------------------------12v round LED button-----------------------
      |                                                                                               |
       And so on . . .

Wire the round LED buttons in parallel with prefab 0.250" daisy-chains if you have any.   




Scott

[RandyT]

  Didn't think about this earlier, but you could just wire the two CDRs in series to drop 4.5v on each.

This probably won't provide the effect desired, unless the wiring is chained without removing the inline resistors.  These are what make them 5v. 

Running LED's at 12v is really inefficient, when there are not multiples in series, as the resistor needs to work much harder.  You can see this when using one of the online calculators.  The same LED which requires a 1/2 watt resistor at 5v, will require a 2 watt resistor at 12v.  In other words, expect it to get a lot warmer, as the differential between it's specified voltage and the supply voltage increases.

Something else to be aware of when running LED's in series is that the best case when one malfunctions, is that all of the units in series will stop working until the bad one is replaced.  Worst case is that you no longer have that voltage drop you were relying on, resulting in the destruction of the others in the series circuit.

[mvolke1]

  Didn't think about this earlier, but you could just wire the two CDRs in series to drop 4.5v on each.

This probably won't provide the effect desired, unless the wiring is chained without removing the inline resistors.  These are what make them 5v. 

Running LED's at 12v is really inefficient, when there are not multiples in series, as the resistor needs to work much harder.  You can see this when using one of the online calculators.  The same LED which requires a 1/2 watt resistor at 5v, will require a 2 watt resistor at 12v.  In other words, expect it to get a lot warmer, as the differential between it's specified voltage and the supply voltage increases.

Something else to be aware of when running LED's in series is that the best case when one malfunctions, is that all of the units in series will stop working until the bad one is replaced.  Worst case is that you no longer have that voltage drop you were relying on, resulting in the destruction of the others in the series circuit.

Randy,

Do you have a lamp I could switch out with the lamp it came with that would work with my other 12v buttons?

[RandyT]

Do you have a lamp I could switch out with the lamp it came with that would work with my other 12v buttons?

No.  You could use one of the low output LEDs, such as those which are used with the buttons, but the light will be MUCH dimmer.  As PL1 suggested earlier, the way to do this would be to add an additional resistor in-line.  A 1 watt 82-ohm would probably do the trick, but monitor the resistor temp to make sure nothing is getting too warm.

If you have a 5vDC power terminal on your USB interface, you could probably get away with two of the CDR units running from it.  But you should check with the manufacturer to see how much current it can deliver.

[mvolke1]

Do you have a lamp I could switch out with the lamp it came with that would work with my other 12v buttons?

No.  You could use one of the low output LEDs, such as those which are used with the buttons, but the light will be MUCH dimmer.  As PL1 suggested earlier, the way to do this would be to add an additional resistor in-line.  A 1 watt 82-ohm would probably do the trick, but monitor the resistor temp to make sure nothing is getting too warm.

If you have a 5vDC power terminal on your USB interface, you could probably get away with two of the CDR units running from it.  But you should check with the manufacturer to see how much current it can deliver.

Hey Randy,

Thanks for getting back to me.

Do you think I could take the lamp from one of these: http://www.arcadeemulator.net/cgi-bin/shop/cp-app.cgi?usr=51F1020295&rnd=7660633&rrc=N&affl=&cip=&act=&aff=&pg=prod&ref=Rectangular+Pushbutton&cat=Low+Profile+Illuminated&catstr=HOME:Pushbuttons:Low+Profile+Illuminated

They look quite similar.

If I did do the resister, where would I add it?

[RandyT]

Do you think I could take the lamp from one of these...

If you would like a standard bulb instead of the LED, I can substitute one for you.  I'm sure I have a bag full here.

If I did do the resister, where would I add it?

It would go between the power supply and one of the wires (in series).  Either wire is ok to do this with.

[mvolke1]

Do you think I could take the lamp from one of these...

If you would like a standard bulb instead of the LED, I can substitute one for you.  I'm sure I have a bag full here.

If I did do the resister, where would I add it?

It would go between the power supply and one of the wires (in series).  Either wire is ok to do this with.

Hey Randy,

I would be more than happy if you have a standard bulb. I just want to make this as easy as possible.

If the standard bulb is just a matter of popping one out and the other in, and it'll work with my adapter safely, I'll be more than happy to do that. How can we make that happen?

[RandyT]

I'll send you an email...

[mvolke1]

Awesome! Thanks Randy!

[PL1]

  Didn't think about this earlier, but you could just wire the two CDRs in series to drop 4.5v on each.

This probably won't provide the effect desired, unless the wiring is chained without removing the inline resistors.  These are what make them 5v.

Yes, I'm referring to using them as delivered with the inline resistor.

If 4.5v is enough to light a CDR -- and it should be -- placing two of them in series will light them just fine with a 9v power supply.

The fact that each is dropping 4.5v instead of 5v means that they are not running at peak current flow.

For example, a 12v LED/resistor combination that draws 20mA when powered by 12v only draws 5.85mA when powered by 5v.

The higher resistance of the 12v LEDs/current limiting resistors in parallel with the CDRs will result in more current flowing the part of the circuit with the CDRs.

To ensure the CDRs aren't damaged, you may need add a resisor in series with the CDRs so that that part of the parallel circuit draws 100mA or less. (verify with your multimeter)


Scott

[mvolke1]

Scott and Randy,

Thanks so much for your help!

I put in an order with Randy, and he's tossing in some extra 12v LED bulbs. I can just switch them out and I should be good to go with my other 12 12v LED pushbuttons.

Thanks again for all your help! When I get them wired up, probably end of week, I'll post some pictures.

Matt

[mvolke1]

Randy,

Thanks for the bulbs! They worked great!

[RandyT]

Randy,

Thanks for the bulbs! They worked great!

No problem   Glad to see you have everything working to your liking!