Resistor calculator program

The Golden White LEDs are still alive and kicking. I can't imagine Richmond Controls recommending the wrong resistor.

Well, duh! (grin) I've already installed one and it's fine, thank you. The reason this discussion is ongoing is to make sure that the resistor calculator programs floating around are actually returning the correct numbers.

No, I was simply using the number you suggested! ;-)

So in more layman's terms, a diode will resist current until its threshold is reached and then pass as much current as is possible up to the point it burns out? The resistor is to limit the current below the burn out point. So in an LED, the idea would be to pass as little current through by using the highest resistance while still getting it to light up.

Is FidoNet still out there? Seems like a long time ago. I don't even remember the node number for my BBS.

"Frank Eva" wrote in message news:dvhRb.108569$ snipped-for-privacy@twister.rdc-kc.rr.com... : "Keith Norgrove" wrote in message : news: snipped-for-privacy@4ax.com... : > So why don't you try it with the 470 as recommended, it will be fine. : : Well, duh! (grin) I've already installed one and it's fine, thank you. The : reason this discussion is ongoing is to make sure that the resistor : calculator programs floating around are actually returning the correct : numbers. : : -- : Frank Eva :

So, did you reach a conclusion?

"E> > Ah, so it is 30ma -- earlier in this thread, you said that it was 3ma -- "E> > did you somehow misplace a 0? "E> "E> No, I was simply using the number you suggested! ;-)

No, somewhere real early in the thread, you said the current rating was

3ma and using 3ma @ 3.5V LED with a 12V supply you came up with 2833 Ohms (which is the *correct* value for such a device with that supply voltage) and suggested that this was wrong. I think this was like the first message in the thread. It appears now that it was a *classic* case of garbage in, garbage out...

AFAIK, *ALL* of the resistor calculator programs are returning the 'right' results, given the inputs entered. At *several* points in this thread, it seems you were entering strange numbers to these (various) programs and getting equally strange results...

"E> "E> -- "E> Frank Eva "E>

"E> "E> "E>

\/ Robert Heller ||InterNet: snipped-for-privacy@cs.umass.edu

|| snipped-for-privacy@deepsoft.com /\FidoNet: 1:321/153

S> Robert Heller wrote: S> > How much voltage a resistor will drop is a function of how much current S> > is flowing. This is where Ohm's Law comes in. A resistor will drop a S> > voltage (V) equal to the product of its resistance (R) and the current S> > (I) flowing through it: S> > S> > V = IR (1) S> > S> > LEDs don't have the same flexibility. They will drop a specific voltage S> > across their junctions, irrespective of the current. Extra current just S> > makes the semiconductor hotter. Too much current and the semiconductor S> > toasts. Ouch! So we need to adjust the resistor to 'balance' the load S> > at a specific current. S> S> So in more layman's terms, a diode will resist current until its S> threshold is reached and then pass as much current as is possible up to S> the point it burns out? The resistor is to limit the current below the S> burn out point. So in an LED, the idea would be to pass as little S> current through by using the highest resistance while still getting it S> to light up.

Something like that. What happens in more detail is that the junction is non-conducting at less than the LED's voltage rating. When the voltage across the junction hits the 'breakover' voltage, it is like a dam that has collapsed and the current will flow, so long as the voltage is at the 'breakover' voltage. The voltage across the LED won't exceed the 'breakover' voltage -- the LED behaves like a short with a fixed, non-zero voltage drop -- eg like a circuit of a 'fixed, non-zero, length' -- essentially, a semiconductor junction is like a self-adjusting resistor, that constantly adjusts itself to some resistance R, such that IR always equals some constant value, the 'breakover' voltage, which is a function of junction's materials. Since I (current) is a effective 'count' of electrons involved and since what a LED is doing is converting electrons to photons, if there are fewer than some number of electrons, the amount of light emitted approaches none as the current is reduced. Above a certain current (number of electrons) the electrical 'friction' causes the semiconductor to heat up and above a certain temperature, the semiconductor stops being a semiconductor...

S> S> S> >

/\FidoNet: 1:321/153 S> S> Is FidoNet still out there? Seems like a long time ago. I don't even S> remember the node number for my BBS.

Yep, FidoNet is alive. How 'well' it is depends... Locks Hill BBS is quite functional.

S> S>

\/ Robert Heller ||InterNet: snipped-for-privacy@cs.umass.edu

|| snipped-for-privacy@deepsoft.com /\FidoNet: 1:321/153

I believe I have - given that the input values are correct, both of the current downloads (Robert Heller's program and Resistor Calculator (author unknown)) are producing the same reliable results.

"Frank Eva" wrote in message news:_1yRb.110651$ snipped-for-privacy@twister.rdc-kc.rr.com... : I believe I have - given that the input values are correct, both of the : current downloads (Robert Heller's program and Resistor Calculator (author : unknown)) are producing the same reliable results. : -- : Frank Eva :

Thanks Frank; I agree. BTW, the Resistor (and LED Current) Calculator I referred you to was developed by Rob Paisley - who has also developed _many_ electronic circuits for model railroading, DC & DCC. His latest is the inductively coupled block occupancy detector for DCC. Check out his home page - Circuit Index - at: Rob has also been a substantial contributor to this NG and to the mrrelectronics Yahoo group.