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RASPBERRY PI and best way to power push button LED

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corrupt27:
Hey guys,

My brother is building a bartop cabinet and is using a raspberry pi. He wants to buy the LED push button controllers. What is the best way to power the LED? Can I use the GPIO? Or maybe the USB Hub that powers the raspberry PI?


Thanks for the help

PL1:
How many LED buttons will he use?

Any idea which specific buttons he has in mind?

Is he planning on using single-color, always-on LED buttons (very easy to do) or is he thinking about using RGB LEDs for different colors and animation? (not sure if anyone has successfully used LED controller boards with the RasPi :dunno)


Scott

corrupt27:
He is planning on 22 buttons.

He wanted them to be constantly on as long as the arcade was on. He was looking at these:
http://www.ultimarc.com/ultralux.html


thank you for the help.

PL1:
You might want to have him check GGG and Paradise Arcade Shop, too.

The Ultimarc ones come with 5 Volt High Intensity LED lamps.
(not sure about the current draw, but 20-30 mA per LED would be a reasonable guess)

The GGG ones come with "superbright" 12v LEDs
(not sure about the current draw in these, but a Paradise 12v superbright powered by 5v draws about 11mA per LED)

My instinct is to recommend the Paradise buttons since they are available with standard 12v LEDs that draw less current.

Paradise 12v LEDs powered by 5v only draw 5.83 mA each. (128.26 mA for 22 of them)

You can use an additional current limiting resistor like R2 on the right half of the diagram below to reduce the current each LED draws.


--- Quote from: PL1 on April 28, 2012, 01:25:00 pm ---I designed my portable modular CP to run off one USB connection that feeds an unpowered hub--maximum 100 mA current draw per connection.

It uses 3 Button Blaster LEDs with resistors from GGG (BB and R1), 14 LED 12V buttons from Paradise(LB), and an 11 ohm current limiting resistor (R2).

------------5V------------------------>
|     |    |           |     |     |    | 
BB  BB  BB       LB   LB  LB  LB (Total of 14)
|     |    |           |     |     |    | 
R1  R1  R1        -------------------->
|     |    |                    |
|     |    |                   R2
|     |    |                    |
-----------Ground--------

The left side is the trackball circuit, the right side is the buttons.
. . .
This whole 17 LED + resistor configuration draws about 81 mA.

--- End quote ---
In this configuration (LED Buttons in parallel + R2) the Paradise Arcade regular LEDs draw 3.7 mA each.

3.7mA * 22 buttons = 81.4 mA

Depending on how much current draw the RasPi can handle, you can use a slightly higher resistor value for R2 to bring the current draw down to an acceptable level.

You can test the current draw for different R2 values using 11 LEDs -- once you get them lighting at or below half the acceptable current draw, you can safely add the rest of the LEDs.

Ultimarc, GGG, and Paradise sell LED daisy chain wiring sets. (you'll need 2 sets for 22 buttons)

The questions to answer now are:

    1. Where do you intend to connect the power for the LEDs? (input power supply, 5v pin on RasPi, separate wall wart, etc.)

    2. How much current can you safely draw from that connection?


Scott

corrupt27:
Hey PL1,

Thank you so much for the great explanation on the wiring and the suggestions on the buttons. But I have no idea where i can draw the power from. Can i get it from the raspberry PI? Or maybe the usb hub. I am not sure. Thats what my original question was for.

Thank you

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