chipmusic.org is an online community in respect and relation to chip music, art and its parallels.
You are not logged in. Please login or register.
hey,
Just got 2 RGB backlights from nonfinite and both came with 1k resistors. This made the backlight way too dim and looked horrible. Was this a mistake, did they send the wrong value?
If you have have one of these backlights( and it is too dim), replace the 1k resistors with 100 ohm. The leds can safely handle the extra current and the result is is much, much brighter more visible display.
Last edited by Charbot (Oct 20, 2010 8:18 pm)
Standard LED protection resistor is 470 ohms, iirc, so really you shouldn't have any less.
Standard LED protection resistor is 470 ohms, iirc, so really you shouldn't have any less.
Depends on the voltage and the LEDs voltage drop. You place a resistor in series with the led to bring the voltage down. if you have the correct voltage for an led to begin with, You wouldn't need a resistor at all.
1k is way too much. for sure.
edit - on the site it says the kit is supposed to include 1k resistors. so it seems intentional, but its simply the wrong value... 1k dims the red LED completely i'd bet, and the blue and green almost totally dimmed. thats strange...
Last edited by kitsch (Oct 20, 2010 10:19 pm)
TraceKaiser wrote:Standard LED protection resistor is 470 ohms, iirc, so really you shouldn't have any less.
Depends on the voltage and the LEDs voltage drop. You place a resistor in series with the led to bring the voltage down. if you have the correct voltage for an led to begin with, You wouldn't need a resistor at all.
Actually no, it depends on the amount of current 
But that's just being somewhat pedantic in this situation, and of course you are actually right (mostly, apart from possibly the last part). I'm just stuck in the mindset of everything = 9v haha. Bad habits from electronics lessons
the point of the resistor is to limit current, you will find that the LEDs work fine without a resistor at all, at least for a little while, but its to do with the way electricity works,
like a lightning bolt, electricity will find the easiest route, so for example if you only put one resistor on the backlight on the common pin, all the power will go through the red because of its lower resistance. in the same way, if you put very low resistors on the LEDs, the power from the gameboy will mainly be going to the backlight and taking power away from the actual gameboy itself.
also resistance is relative, so saying there is a set resistance to use with LEDs is wrong because it depends on the supply voltage and current, in the case of 5v that the gameboy supplies 220 ohm is pretty good, having said that if you look at my RGB gameboy all the lights in that are using the 1k resistors and they are fine,
if your backlight is dim or unevenly lit, then it maybe bad wiring, bad batteries, a dodgy source of 5v (take it straight from the regulator) or it maybe that over powering the LEDs has weakened them so they have to be powered with a low resistor value to get any light at all.
Of course the current matters. It's all Ohms law. But to say that the resistor is there to limit current is simply not right. You alter the brightness of an led by changing the voltage over the resistor not the current through it.
E.g. A standard red led with a voltage drop of 3v and that draws 20mA. You wish to hook this up to a 5v source. Then the aim is to lower the voltage from 5 to 3 volts. (5-3) / 0.02 = 100. 100 Ohms should be the lowest resistor value to use.
Of course the current matters. It's all Ohms law. But to say that the resistor is there to limit current is simply not right. You alter the brightness of an led by changing the voltage over the resistor not the current through it.
Well, yes and no. An LED (and indeed, any diode) is fundamentally different from a resistor with regards to its voltage/current response.
A resistor has a linear response. Double the voltage over a resistor and you also double the current. Easy as a pie.
For a diode, on the other hand, the current increases exponentially with an increasing current. Double the voltage and the current increases thousandfold or something like that. See this graph. The term "forward voltage drop" is actually an arbitrarily defined point on this graph denoting a voltage that is "ideal" i.e. high enough to allow the diode to carry current, but low enough that current doesn't sky-rocket exponentially.
So what does this mean? Well, keep in mind that current and voltage are not separate entities, but completely interrelated. Any change in current is also a change in voltage and vice versa. In this context, they are just the same measurement expressed in two different ways (either as charge or as flow of electrons.) In reality, the "forward voltage drop" defines not a point, but a small range of a few millivolts where the voltage stays roughly constant while the current varies over a quite large range. (Maybe 5-40 mA for a regular LED 5 mm LED.)
So, does the resistor control current or voltage? It controls both, as voltage and current are closely related. However, it's much more relevant to say that it controls current as current is the unit that changes the most when you vary the resistance. (At least as long as you stay near the "voltage drop".)
I hope that clarified some of the theory behind LEDs (or if not, piqued someone's interest.)