FreeTrack Forum

Hi all,

I've purchased the following LEDs (x3) and intend to wire them in series.
http://www.maplin.co.uk/Module.aspx?ModuleNo=2253

The tech guy at Maplin's thinks they will be fine to wire up to a USB power source without any resistor(s) involved.
Before I go ahead and try it, is he correct?

If not then which values should I use for the LED wizard?

Cheers

Kongio

I used the exact same LED's, but with a 9v battery and I can assure the guy at Maplin is talking crap, you will need at least a 15ohm  resisitor if you want to ensure those LED's don't burn out.

Also those LED's require filing down as they have a very narrow view angle although they do work quite well once you have done so.

What I'd suggest is a resistor somwhere between 30 and 20 ohms (30ohms gives you 50mA of power 20ohms gives ya 70mW)

Values for LED wizard are

voltage value =  5 (usb is 5v)
power supply = USB
Forward voltage = 1.2
Forward Current = 65 (50 min - 70 max)



You should also take heed of the warnings on here regarding protecting your motherboard from damage

Attempting to use USB as a power source can permanently damage your motherboard if you're not careful, if you feel competent enough to use it, make sure you include a PTC fuse with a 0.2A current cutoff in your circuit as insurance.

so if you change the power source use the same Forward current and Forward voltage values as above but adjust the voltage value to suit your power method

That's great!

Cheers for your help Desrat

Kongio