The Cthulhu board and installing leds ! need information, thanks!


#1

Im planning to install Seimitsu translucent pushbuttons with leds behind them.
I don’t want the leds to light up only when pressed but to be on all the time when i plug in the stick (via USB)

I will be using also the Cthulhu board to build my arcade stick. Im already aware that the Cthulhu board has a 5v power supply.

Im thinking of using leds like these :

http://www.dealextreme.com/details.dx/sku.1106

Now when i want to make a led circuit, does it go from powersupply to resistor, then to first led - 2nd led etc and finish into a ground on Cthulhu board ? would that work or is there something im missing ?

Are theses leds bright and small anough ?
What power resistor do i need ?

Any advice is appreciated guys.


#2

You should mention how you want the LEDs to behave. If you want them on when the button is pressed the ‘light up button thread’ (I forget the name. Pretty sure started by TingBoy) should have everything you need including resistor information and the chip needed to make it work.


#3

Id like them to be ON ALL the time, not when pressed. :slight_smile:


#4

Ah :slight_smile:
Assuming they have a voltage drop of 1.5v (there’s no datasheet for those for me to check but this should be the case for most) then the voltage after the LED should be about 3.5v. We want to limit the current to 20mA. What I’d suggest is pick up a big bundle of resistors from Radio Shack or Fry’s. Make sure they have about 220 Ohm, 330 Ohm, and 1k ohm resistors. Start with the 330 Ohm resistors first. If the bundles at radio shack or fry’s doesnt have these values (they are very common values) then just order a bunch online from newark.com, jameco.com or digikey.com. They’re damn cheap.

Run a wire to the VCC screw terminal on the Cthulhu. Solder 6 (or eight, one for each LED) wires onto the end of the VCC wire. Connect the positive leg of the LED to the wire, connect the resistor to the other leg of the LED, and connect the other leg of the resistors together and run a wire from the collection of resistor legs to ground.
If its too bright at 330 Ohm, try the 1k (it’ll be safer too since it uses less power). Try the 220 Ohm if you want brighter, but please try the 330 ohm first, Do NOT go less than the 220 Ohm!!

Yes, you want to wire them in parallel, using one resistor for each LED. Yes, there is a reason for this that’d take too much time to 'splain. Trust me.

For wattage, I’d say go with 1/4 watt. 1/2 watt works too. 1/8 watt could work, but I’d prefer you use 1/4 watt or larger.


#5

I understood most of this and can create a mental image of it all but the end lost me…

Whats up with the wattage ?


#6

Forget I said anything; you’d have to actually hunt for a resistor that wouldnt work. Just make sure NEVER less than 200 ohms.


#7

Is some kind of speaker wire (red and black) tough anough for 5v ?

Ok, so ill use these leds with these resistors :

http://cgi.ebay.ca/330-ohm-metal-film-resistors-1-4W-1-100pcs_W0QQitemZ140291157877QQcmdZViewItemQQptZAU_B_I_Electrical_Test_Equipment#ebayphotohosting
http://www.dealextreme.com/details.dx/sku.1106


#8

Speaker wire is overkill, lots thicker than you need, but it will work, sure.


#9

I use speaker wire,

comes in thinner gauges also


#10

Toodles great info there. From what I understand you daisy chain the led’s anodes to 5VCC on CTHULHU. Connect 1 resistor of 220 Ohm and upwards to each led. And then Daisy chain the cathodes to a ground on CTHULHU. I suppose the method applies in general for leds of 3.3v. I have 2 questions to ask:
If I use 3mm superbright leds (3.3 volt only info provided be seller) do I use different resistors?
How many leds can I power in this way via CTHULHU? Is it possible to power 16 leds 5mm or 3mm 3.3v with the method you mention?
Thanks for your time mate. (and keep working on that flash mod :slight_smile: you rock)