LED questions

[diluzio91]

So i know i've been inactive for a while here, but I'm going to be building a custom controller for a friend, and have some questions about switches, and led's.

Basically this is going to be a fight stick for an xbox 360, I have the buttons and the joy stick already for it, i just need some help on the following.

Lighting: I'm planning on using a vandal switch for the home button on the controller, as well as the rest of the lighting by leaching power from the USB+5v Line. How many lights can i really run doing this? The plan so far is 1 lit vandal momentary switch for the home button, and 2 led's hooked into the controller at the 1 and 2 position to show which player is up.

Buttons: Does anyone know of a good matte black switch about 1/2 in across (momentary) that i can use for the back and home buttons?

There should be a work thread up soon as well... I've been busy, and it feels good to be back.

[TLHarrell]

If you're talking just the LEDs for lighting up the buttons, you should easily be able to supply the power from the one USB connection. I've run dozens from a couple AA batteries in model lighting. Of course, this depends on their power draw. Brighter ones draw more.

If you purchased them from somewhere that gives out the specifications, then get the forward voltage drop and current (in mA) for the LEDs. You can then easily toss these figures into an LED resistor calculator and see how they'll do. Total up the mA draw for all the LEDs and check it against what your 5v supply will produce. Some USB connections will supply more power than others.

[diluzio91]

i can probably stick a multi meter into a 360 usb to see how many amps are being pushed through, i'm lazy, so i'll just cheat and run 5v leds... i usually buy from ledshoppe, and they're pretty good about listing the specs

[mDust]

Originally Posted by diluzio91

i can probably stick a multi meter into a 360 usb to see how many amps are being pushed through, i'm lazy, so i'll just cheat and run 5v leds... i usually buy from ledshoppe, and they're pretty good about listing the specs

If you're looking for the max current the line can provide, it's 5A...to a charging device. I'm not sure how it would know where the power was heading, but I assume the authors weren't anticipating modders splicing into it for their own nefarious purposes.
http://en.wikipedia.org/wiki/Univers...al_Bus#USB_2.0

I personally wouldn't try to draw 5 amps from it. I'm sure it can technically provide more, considering engineers and their safety factors, but I've found it's best to just not push things to their limits unless the device is expendable. Just divide, say, 4000-5000mA by whatever mA rating you get from the above mentioned LED calculator or the mA rating at the peak voltage applied across the LEDs in series.

[r0adawg]

I'm betting that the xbox 360 has a max of 500mA per port. Granted the spec does allow for higher power (3.0 supplies 900mA), most usb(2.0) ports provide 500mA at most.

[mDust]

Originally Posted by r0adawg

I'm betting that the xbox 360 has a max of 500mA per port. Granted the spec does allow for higher power (3.0 supplies 900mA), most usb(2.0) ports provide 500mA at most.

After reading this and then digging a little further, this seems to be true. It's pretty lame that manufacturers limit hardware that far below spec to save pennies. If I want 5A via USB, I should be able to get it! +rep r0adawg

[TLHarrell]

The majority of LEDs out there are very happy with 3-3.3vDC. Some are rated to be supplied 5v, but may be more difficult to get. 5vDC from a USB port is fine for 1 LED in series with an appropriate dropping resistor. Two in series (2.5vDC) will likely either be super dim or not light at all.

mA rating for power feeds is rated to the weakest link in the chain. To draw a 5A load, you would have to have a USB cable with thicker gauge wiring, which would cost more to produce. Beyond that, all the traces on the board from power supply to the USB ports would have to be thicker and likely shielded somehow to eliminate induced currents to other traces. This all adds (in the manufacturer's mind) needless cost.

You might look into tracing another 5v power source either at the power supply, or installing the guts of a wall wart within the device, wired back to the power input connector, with a slightly higher rated load capacity.

[mDust]

Originally Posted by TLHarrell

The majority of LEDs out there are very happy with 3-3.3vDC. Some are rated to be supplied 5v, but may be more difficult to get. 5vDC from a USB port is fine for 1 LED in series with an appropriate dropping resistor. Two in series (2.5vDC) will likely either be super dim or not light at all.

mA rating for power feeds is rated to the weakest link in the chain. To draw a 5A load, you would have to have a USB cable with thicker gauge wiring, which would cost more to produce. Beyond that, all the traces on the board from power supply to the USB ports would have to be thicker and likely shielded somehow to eliminate induced currents to other traces. This all adds (in the manufacturer's mind) needless cost.

Some 3mm red, orange or yellows could probably be 2 in series plus resistor. Larger bulbs or short wavelength colors will probably only fit one. With a max forward voltage of ~2.8, 2 bulbs in series sans resistor would work.

I'm not sure if the USB power lines are 'smart' or otherwise 'need' to run through the circuitry, but couldn't one splice those lines directly to the 5v PSU lines? Then just figure out the max safe current for that wire gauge.

[TLHarrell]

USB power are not smart. The device will draw the current it is designed for, up to the limitation of the port. If you isolate the power connection from a USB port, you can feed that part of the port from elsewhere up to the limits of your heaviest gauge wiring in the circuit.

Just for illustration, a 12v car battery supplies many amps. Connect a small 12v device to it, and it won't blow up because the device only draws what it needs. Feed it double the voltage though and It's toast.

[mDust]

Originally Posted by TLHarrell

USB power are not smart. The device will draw the current it is designed for, up to the limitation of the port. If you isolate the power connection from a USB port, you can feed that part of the port from elsewhere up to the limits of your heaviest gauge wiring in the circuit.

Just for illustration, a 12v car battery supplies many amps. Connect a small 12v device to it, and it won't blow up because the device only draws what it needs. Feed it double the voltage though and It's toast.

I was suggesting that just because there is a much greater supply of current from the source doesn't mean it can all be safely utilized on the led/controller end. I don't always clearly communicate my thoughts.
Since it's not my project, I'm too lazy to look up the wire gauge common to USB. I'm sure it's close to maxed out at 500mA due to penny pinching though. To light up that controller properly, a wire upgrade is likely necessary. Depending on diluzio's plans, this project may be getting complicated. aka fun.

First we need OP to return to this thread. Then we need pics.