LED resistor: smaller value = brighter?
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I've been working on a project invovling MIDI & illuminated buttons
(thanks again to those who answered my previous questions, everything
is working great so far!)
I put in 470 Ohm resistors between stamp pins & the LEDs in the
buttons because that is what everybody seems to be using. But I'd
like the LEDs to be a little brighter. IF I use a 220 Ohm resistor
instead will the LEDs be brighter? They're just standard LEDs inside
the buttons.
Because I'm lighting up to 5 LEDs at once, I've got a darlington
array in there, and I'm using a voltage regulator (not the one on the
BS2)
Any help appreciated, and if anybody else is building a talkback
system for a Yamaha 01v I'll be happy to share some sysex codes....
-DL
(thanks again to those who answered my previous questions, everything
is working great so far!)
I put in 470 Ohm resistors between stamp pins & the LEDs in the
buttons because that is what everybody seems to be using. But I'd
like the LEDs to be a little brighter. IF I use a 220 Ohm resistor
instead will the LEDs be brighter? They're just standard LEDs inside
the buttons.
Because I'm lighting up to 5 LEDs at once, I've got a darlington
array in there, and I'm using a voltage regulator (not the one on the
BS2)
Any help appreciated, and if anybody else is building a talkback
system for a Yamaha 01v I'll be happy to share some sysex codes....
-DL
Comments
(less resistance)
until around 20 to 35 mA (depending on the LED),
when it becomes very bright for a short time and
burns out. Most 'normal' LEDs will do 25 mA.
The standard LED equation is:
(VCC - Vled) / SeriesResistance == LEDCurrent.
(5 Volts - 1.4 Volt LED) / 25 mA == 144 ohms.
So, 144 ohms is the SMALLEST resistance.
Note from 15 to 25 mA you don't see a lot of
difference in intensity.
(5 volts - 1.4 volt LED) / 220 ohms == 16 mA,
which would be typical (and safe).
Note the Stamp maxes out at 60 mA total for all I/O
pins added together -- but you mention darlingtons,
so you know about that.
--- In basicstamps@yahoogroups.com, "futilityengineer"
<futilityengineer@y...> wrote:
>
> I've been working on a project invovling MIDI & illuminated buttons
> (thanks again to those who answered my previous questions,
everything
> is working great so far!)
>
> I put in 470 Ohm resistors between stamp pins & the LEDs in the
> buttons because that is what everybody seems to be using. But I'd
> like the LEDs to be a little brighter. IF I use a 220 Ohm resistor
> instead will the LEDs be brighter? They're just standard LEDs
inside
> the buttons.
>
> Because I'm lighting up to 5 LEDs at once, I've got a darlington
> array in there, and I'm using a voltage regulator (not the one on
the
> BS2)
>
> Any help appreciated, and if anybody else is building a talkback
> system for a Yamaha 01v I'll be happy to share some sysex codes....
>
> -DL
also overdrive the LED and burn it out.
With regards to driving LED's you need to know what voltage and
current the LED is rated at. And, with these two values you can
determine the optimum value for your resistor that will be required
based on you supply voltage. This optimum value will give you
maximum brightness for that LED, without burning it out.
The way you determine this value is described in great detail on Al
Williams site at http://www.wd5gnr.com/basiccir.htm
But, basically, you can use the folowing formula:
Supply Voltage - Rated Dropout Voltage of the LED
Rated current used by the LED (amps)
For example, say you have an LED rated at 1.2V@10mA and you have a
supply voltage of 5 then you have:
5 - 1.2 3.8
= --- = 380 ohms
.01 .01
All this is great assuming you know the values in which the LED is
rated. If not, stick with the 470 ohm resistors so you can be safe
not to burn them out.
-Dustin
--- In basicstamps@yahoogroups.com, "futilityengineer"
<futilityengineer@y...> wrote:
>
> I've been working on a project invovling MIDI & illuminated buttons
> (thanks again to those who answered my previous questions,
everything
> is working great so far!)
>
> I put in 470 Ohm resistors between stamp pins & the LEDs in the
> buttons because that is what everybody seems to be using. But I'd
> like the LEDs to be a little brighter. IF I use a 220 Ohm resistor
> instead will the LEDs be brighter? They're just standard LEDs
inside
> the buttons.
>
> Because I'm lighting up to 5 LEDs at once, I've got a darlington
> array in there, and I'm using a voltage regulator (not the one on
the
> BS2)
>
> Any help appreciated, and if anybody else is building a talkback
> system for a Yamaha 01v I'll be happy to share some sysex codes....
>
> -DL
maximum current allowed. Most LED's will tolerate 20ma. but you must check
your particular ones. Use ohm's law to determine the resistor value to use.
divide the supply voltage by the current to get the resistance. For example
5 volts devided by .02 amps (20 ma.)= 250 ohm so 220 ohm resistors would
exceed the 20 ma. rating. By the way, you want to have a separate resistor
for each LED, not a common one for all the LED's.
Original Message
From: futilityengineer [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=LdmAaggTc0ejO5TK1OGsBPZCmA_fFWg8Tnj7kXolVdhjiecAOWfzGk8pcvCkrVNviJY1OUIKdAwLpB_E6BtDNJ9P4Hs]futilityengineer@y...[/url
Sent: Monday, March 10, 2003 1:29 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] LED resistor: smaller value = brighter?
I've been working on a project invovling MIDI & illuminated buttons
(thanks again to those who answered my previous questions, everything
is working great so far!)
I put in 470 Ohm resistors between stamp pins & the LEDs in the
buttons because that is what everybody seems to be using. But I'd
like the LEDs to be a little brighter. IF I use a 220 Ohm resistor
instead will the LEDs be brighter? They're just standard LEDs inside
the buttons.
Because I'm lighting up to 5 LEDs at once, I've got a darlington
array in there, and I'm using a voltage regulator (not the one on the
BS2)
Any help appreciated, and if anybody else is building a talkback
system for a Yamaha 01v I'll be happy to share some sysex codes....
-DL
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darlington array, and use the 2803 output to ground the diode and turn
it on (a pull-up resistor is also used). I vary the diode intensity
independently with a small-valued pot (or fixed R) in series with the
+5v power to the diode.
Dennis
Original Message
From: futilityengineer [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=BOOmnB6Aw92prQLPEpBGIUYvw-xVHEWa1oEEWltwYuW1ovZfUEnDJANAJfF0ne-AaZr-5KskaY98rj3_IXmBZqU]futilityengineer@y...[/url
Sent: Monday, March 10, 2003 10:29 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] LED resistor: smaller value = brighter?
I've been working on a project invovling MIDI & illuminated buttons
(thanks again to those who answered my previous questions, everything
is working great so far!)
I put in 470 Ohm resistors between stamp pins & the LEDs in the
buttons because that is what everybody seems to be using. But I'd
like the LEDs to be a little brighter. IF I use a 220 Ohm resistor
instead will the LEDs be brighter? They're just standard LEDs inside
the buttons.
Because I'm lighting up to 5 LEDs at once, I've got a darlington
array in there, and I'm using a voltage regulator (not the one on the
BS2)
Any help appreciated, and if anybody else is building a talkback
system for a Yamaha 01v I'll be happy to share some sysex codes....
-DL
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject
and Body of the message will be ignored.
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extra bright.. Use a lower value resistor, I wouldn't go under 180
ohms or so, and use the PWM command to control the apparent
brightness of the LED. Since you're pulsing the LED very fast, and
it's off for a short period of time between each on pulse, it has
time to cool off and recover. You can adjust the PWM amount to get a
nice 'twinkle' from the LED. Radar transmitters use this same
principle to get many thousands of watts from a device that's only
capable of a couple hundred watts in continuous operation. It's
called 'duty cycle.'
-Jorth-
--- In basicstamps@yahoogroups.com, "futilityengineer"
<futilityengineer@y...> wrote:
>
> I've been working on a project invovling MIDI & illuminated buttons
> (thanks again to those who answered my previous questions,
everything
> is working great so far!)
>
> I put in 470 Ohm resistors between stamp pins & the LEDs in the
> buttons because that is what everybody seems to be using. But I'd
> like the LEDs to be a little brighter. IF I use a 220 Ohm resistor
> instead will the LEDs be brighter? They're just standard LEDs
inside
> the buttons.
>
> Because I'm lighting up to 5 LEDs at once, I've got a darlington
> array in there, and I'm using a voltage regulator (not the one on
the
> BS2)
>
> Any help appreciated, and if anybody else is building a talkback
> system for a Yamaha 01v I'll be happy to share some sysex codes....
>
> -DL
did the same thing with a standard 3-volt flashlight bulb way back when.
Pumped it with 9 volts for a *very* brief period of time and it was bright
enough to see from 2-3 blocks away.
You could always break down and buy some super-bright LED's. These things
are fairly bright even when pulsed, and you don't need to push them to their
max rating to do it. I've got some T1-sized LED's I used to replace some
small 12-volt bulbs. I run them at their rated current and they are way
brighter than the bulb -- so much so they almost blind you at night.
Original Message
> I had a similar problem and burned up several LEDs trying to get them
> extra bright.. Use a lower value resistor, I wouldn't go under 180
> ohms or so, and use the PWM command to control the apparent
> brightness of the LED. Since you're pulsing the LED very fast, and
> it's off for a short period of time between each on pulse, it has
> time to cool off and recover. You can adjust the PWM amount to get a
> nice 'twinkle' from the LED. Radar transmitters use this same
> principle to get many thousands of watts from a device that's only
> capable of a couple hundred watts in continuous operation. It's
> called 'duty cycle.'
> > I've been working on a project invovling MIDI & illuminated buttons
> > (thanks again to those who answered my previous questions,
> everything
> > is working great so far!)
> >
> > I put in 470 Ohm resistors between stamp pins & the LEDs in the
> > buttons because that is what everybody seems to be using. But I'd
> > like the LEDs to be a little brighter. IF I use a 220 Ohm resistor
> > instead will the LEDs be brighter? They're just standard LEDs
> inside
> > the buttons.
> >
> > Because I'm lighting up to 5 LEDs at once, I've got a darlington
> > array in there, and I'm using a voltage regulator (not the one on
> the
> > BS2)