LED calculator

If you feel the need to discuss, you came to the right place to do it.
http://www.bit-tech.net/article/68/

 

Scene as knowone else has made a comment, I thought I would start the ball rolling

Looks useful, and I may end up using it at some point in the very near future

You have certainly added some new ideas to the BiT-Tech crew, and there is a different style of article, which is nice for a change, and it makes BiT-Tech all the more better.... I am sure I am not alone in thinking that BiT-Tech made a very good decision in taking you on

BiT-Tech becomes ever stronger as the days go by

 

Anyway you can put it on the site as a downloadable Excel file?

 

Agreed. A downloadable executable program would be even better

 

Wow that is great!! v.v. useful m8, i will be using that for the future

Only concern is - what happens if u have 5v (/7v/12v) LEDs? the Diode forward voltage only goes from 2-4v

edit: ahhh it *does* work for a greater voltage then 4v.. just - i dont understand the description to the right now?!

anyhow - gj lin

 

LEDs themselves only really drop 2-4 Volts. When you say "a 5V LED" you're talking about an LED that's packaged with a resistor or some other protective circuitry.

Series combinations will add up to haigher voltage drops, that's the main reason for the ability to put high numbers in. Parallel combinations you need to add up the current ratings. That's why I let you enter higher numbers for current. That's also why I calculate the power dissipated in the resistor--parallel combinations can draw serious current and require a power resistor. The bracketed values on the form are typical for a single conventional LED. I do have sanity checking in the calculator code to prevent you from specifying things like Vf > Vs for instance.

 

is there a way to d/l that or can i count on you guys to keep it up forever..........

i really want to beable to have that calculator to use at any time

or is there a formula i can plug into my calculator?

 

Linear, do you mind if I use some of your calculations to turn the calucator into a standalone application?

Sean

 

On another note, there seem to be problems with the colours returned by the calculator for certain resistor values. For instance, try inputs of 24, 7, 10. The value returned is 1800 ohms, so colours should be brown grey red. The calculator gives brown green red.

Sean

 

Well, I've made the EXE, and I've found some webspace to host it on! Linkage: http://www.geocities.com/seanblee/rescalc.zip

Sean

 

Sean, I have passed on your email to Linear

 

sean - that link dont work

i use hosting from neoagent.net and i like it a lot, try it

 

Koolvin - thanks mate!
As for the link, it is working, it's just Geocities. It wasn't earlier, hence the edit on the post to change the URL, but it should be now. I think as a temp. measure, I'll stick it on my other space, but don't tell anyone ;-) Try http://www.disco2.com/sean/Rescalc.zip.

Sean

 

That bug is now squashed. There was a duplicate entry in the array of color code strings.

 

We can keep it up forever

But you can also save the page it's on, it executes entirely in your browser.

And of course there's a formula:

R = (Vs - Vf) / Id (make sure Id is in Amperes)
P = (Vs - Vf) * Id

 

UPDATE

W00t! the Luxeon Star/O b0rked my calculator!

Or at least my assumptions. The calculator now correctly deals with resistor values down to 1 ohm, so it can deal with absurdly high current LEDs like the Luxeon, and even in parallel combinations.

 

How to enter LEDs in Series?

I under stand how to enter the values in for the LEDs, but if you put more than 1 led in the circut, do you double both the forward votage and the current, or just the voltage? Sorry, I have some electrical knowledge but not a whole lot. (I am used to dealing with pre-wired applications for automotive stuff) Thanks!!

 

Welcome to the boards.

For series, add the forward voltages. For parallel add the currents.

 

Another dumb question

Sorry, one more question. . . . 1/2 watt or 1/4 watt resistors?? Sorry to take up your time with these simple questions, but again I am used to pre-wired applications. This is my first venture into the land of the create-your-own-mod!! I am hoping to build my own case out of Lexan© soon!! I'll try to show some pics when it is done.

 

I usually use 1/4W, and I buy them in 500-piece assortments most often.

One cool trick is if you need say a 47 ohm, 1/2W, you could use two 100 ohm, 1/4W in parallel. The wattage ratings are additive in parallel even though the ohms aren't.

But the rationale for having the power rating calculated along with the ohms is this exact issue--if you are running a high supply voltage, sometimes the resistor would need to be a bit bigger than 1/4W. If you get a result for power dissipated in the resistor over say 220 mW, I'd consider a 1/2W resistor instead. That's almost never a problem with single LEDs unless you use 12V instead of 5V supply.