# Beer Pong Table with LEDs!!!! Help

Discussion in 'The Projects Forum' started by adamcswant, Mar 23, 2011.

Mar 23, 2011
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So the plan is to put leds all on the perimeter of the table and have a few under each cup. My question for everyone is how do I power the leds? What parts will I need?

For the border I'm using 240 green, 240 red, and 240 yellow leds. Their forward voltage is 3.2, 2, 2.2 respectively @ 25 mA.

Originally the plan was for it to run off of batteries... like D-Cells, but it may be just to much to ask from batteries.

P.S. It's a Bob Marley themed table. Pics will definitely be posted of the finished product.

Apr 5, 2008
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Mar 23, 2011
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Thanks for responding. Unfortunately, I'm looking for a basic guide on how to just turn them all on... no flashing or chasing... I just want them to get power. This is my first real LED project, and I know I picked a HUGE first project... but hey it's go big or go home right? What resistors would I use? How many in a series? Do I need drivers? how big of a power supply would I need?

Apr 5, 2008
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5. ### Bernard AAC Fanatic!

Aug 7, 2008
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A simple bare bones setup would use a regulated 24 V powersupply rated at something over 2A. 48 V would be even better to reduce number of strings. As a first guess allow 20V for LEDs & 4v for resistor @ 20mA.
G-240-@-3.2V-= 6 LEDs per series string--= 40 strings with 240Ω / string.
R-240-@-2.0V-=10 '' ' ' ' ' ' '------------- --=24------ ' ' ' '' 200 ' / ' ' ' ' ' .
Y-240-@-2.2V-=9 ' ' ' ' ' ' ' ' ---------------=17 ' ' ' ' '------ 210 ' / ' ' ' ' '.
Total strings = 91 @ .02 = 1.8
Just to give a rough idea of scope of project.

Last edited: Mar 25, 2011
6. ### Wendy Moderator

Mar 24, 2008
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Personally I would limit the power supply to 24VDC and double the current. BG Micro still sells their 24VDC 6.5A power supply for \$15 I believe. 48V is just a bit too much voltage for my comfort, though I suppose it is safe enough.

7. ### Bernard AAC Fanatic!

Aug 7, 2008
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397
\$ 15 for 24V @ 150W- Wow-- go for it.

8. ### Wendy Moderator

Mar 24, 2008
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I have two in storage, but I still see them kicking around. They aren't uncommon. I was just suggesting it as a possibility for the OP.

http://www.bgmicro.com/PWR1278.aspx

I've also seen them elsewhere.

Mar 23, 2011
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That sounds like a pretty good deal! So if I were to use one of those power supplies how would the wiring go and what resistors would I use? Also, where's a good place to get bulk wire for this project? I'm starting to realize I'm going to need quite a bit.

10. ### Wendy Moderator

Mar 24, 2008
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See post #4, that is a tutorial I made for LEDs. Focus on all of chapter 1 and the first half of chapter 2.

I would read it, try to use it, then post the results on here for critique. For a project like this you're going to have to learn the math, I don't see any way around it.

If you have a digital camera or a flat bed scanner you can draw schematics and upload them as attachments.

Mar 23, 2011
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So basically this is the layout I'm thinking as far as having a PS with leads that go all the way around the table with the led series branching off... That should work, right? And then of course the finished diagram would have quite a few more series on it... but that's a lot of drawing...

Any help is always appreciated!

12. ### SgtWookie Expert

Jul 17, 2007
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You might consider using CAT-5 cable. It has 4 pairs of AWG-24 copper wire (8 conductors) - you can pull it apart and use the individual wires.

13. ### SgtWookie Expert

Jul 17, 2007
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Know that you can mix colors of LEDs in a series string - as long as they all require the same current. Just add up the forward voltages.

Leave yourself at least 1-2 volts for the current limiting resistor. Much less than that, and you may run into problems due to heat (the Vf of an LED decreases with an increase in temperature).

Mar 23, 2011
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1.) Ok so lets say I hookup 3-Green @3.2Vf, 3-Yellow @2.2Vf, and 3-Red @2Vf in sequence...
This equals a total of 22.2v.... meaning if I'm using a 24v PS I need a 100ohm resistor to tun them at 20mA?

2.) Why on some sites do I see diagrams with the resistor on the anode of the first LED and on others they put it on the cathode? Does it matter?

15. ### SgtWookie Expert

Jul 17, 2007
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1,728
Rlimit >= (Vsupply - (Vf_LED_total)) / Desired_Current
Rlimit >= (24v - 22.2v) / 20mA
Rlimit >= 1.8v / 0.02a
Rlimit >= 90 Ohms.
90 Ohms is not a standard E24 value of resistance.
A standard table is here: http://www.logwell.com/tech/components/resistor_values.html
Bookmark/favorite that page.
Looking at the E24 (green) columns, you can see that 100 and 91 (910/10) are standard E24 values. 91 Ohms is the closest to 90 Ohms that is >= to it.

1.8v / 91 Ohms = ~19.78mA
Then you need to calculate the resistor wattage requrement.
RWatts >= V(Rlimit) * I(Rlimit) *2
The *2 is for reliability.
So: RWatts >= 1.8v * 0.01978a * 2 = ~ 71.2mW - you can use 1/10 Watt (100mW) or greater for this resistor.

You can also go with the 100 Ohm resistor. This will provide 1.8v/100 = 18mA current through the LEDs, which will help to extend their lives.

The current limiting resistor can actually be anywhere in the series string.
I prefer to use them between Vsupply and the most positive anode.

Mar 23, 2011
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So I've got all the leds, resistors, and power figured out. THANKS!

Any advice on how to join all the 24awg wires coming from each series and plugging them into the terminal on the power supply?

Or should I run a higher gauge like 14 or 16 around the edge of the table and branch each series off of it like in my previous sketch?

Mar 23, 2011
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Lol... so now that they are all lit... are we talking rocket science to make them chase? I read the tutorial but I'm still lost as to how I would be able to make 200+ leds chase.

18. ### Wendy Moderator

Mar 24, 2008
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The key is to wire the LEDs correctly, not to have 200 sequences.

Let's take a look at figure 9.2

You have 4 LEDs on at any one time, but they are are 1 of 4 that are on. The set of 4 chase each other endlessly.

Each chain is a sequence. A 4022 chip has 8 outputs, only 1 of which is on at any one time, and in this case it has been limitied to 4 sequences. The 4017 has 10 outputs, but is the same. Each output is a sequence. So if you have 200 LEDs, and 10 sequences, you will have 20 LEDs being driven from the 4017 at any one time. This will require transistor drivers, but is no big deal.

We have a PCB design elsewhere that use 3 4017's to make 25 sequences, so you have some options.

Looke at the LED illustration on the side of figure 9.2. Note which ones are lit during each step. It is very much like an animation, as it steps it light appears to move forward.

If a chip can do 10 steps the number of steps can easily be reduced from there. Same with the PCB that does 25 steps.

So it is like animation, you think how many pages (steps) you have, then figure out which LEDs are on for each page.

You have a fairly big project, so you will have to do some drawing just for the layouts.

Last edited: Mar 29, 2011

Mar 23, 2011
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So I have 236 green leds going around the outside, 228 yellow, and 226 red.

So the green circuit has 59 leds per channel if I want every 4th led lit up. In that diagram where do I put the resistor that controls the resistance for each channel of leds? Can I put series attached to a channel?

20. ### Wendy Moderator

Mar 24, 2008
20,766
2,536
OK, you will have some trouble with that, nothing major, but there will be a minor blip. Since the number of LEDs are not divisible by 4 on the sides (59 LEDs per side) the chase will have a blip. This is the blank, no LEDs lit.

This is the first frame of four, with one sequence lit...

Notice the two LEDs lit next to each other? If you want I can finish the drawings to show how it would look. You could just ignore blip, it may not be that noticable. Or decrease the number of LEDs by four.

****************

Thinking about it, I must have a drawing error in here somewhere. It should have worked. The total number is divisable by four, which is all that is important. The next drawing shows how the animation would work though, plus I improved the size a bit.

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• ###### BT1.PNG
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Last edited: Mar 29, 2011