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January 22, 2008
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about 3 weeks ago
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about 10 months ago
I’m having some unexpected behavior from the PicoBuck.
I am running only two channels. One with a Red “3 Watt” LED and one with a Blue “3 Watt” LED.
I am powering this with the +12vdc rail of an old PC power supply. I am controlling each of the channels with a separate PWM output from a Arduino Nano. I am reading two separate pots to set the output value used to drive each channel. [pseudocode analogWrite (BlueLEDpin, analogRead((BluePot)/4)]
The problem is, it appears I have a lot of cross talk between the two channels. If only one channel is connected, I can control it’s brightness without issue. But, if I have two channels running, both pots change the brightness of both LEDs.
Using serial.Print shows that each value being written out is in the expected range of 0-255. There is no cross control happening there. This leads me to believe the issue may be in the PicoBuck it’s self.
I looked into the specs on the AL8805W5 and found it works more reliably with <= 500Hz control signal.
Since I am using pins 5 & 6 from the Arduino, I may be getting ~980Hz . Additionally, pins 5 and 6 use T1 for timing, as does the “delay()” command. These two items combined may be causing the issue.
More testing later. I will post the results [/EDIT]
Yes, it is as I expected, using D5 & D6 for PWM output, along with code that includes “delay()”, is NOT a good idea.
I simply moved the control signals to D10 & D11 and the PicoBuck worked perfectly.
I am tempted to remove my original post, but if it helps someone else to fix a problem, then I am happy to leave my oversight posted. [/EDIT2]
about 11 months ago
OK, now we are on the same page!
“Remember 3W is the limit of these LEDs, not the amount of power they will use.” WHAT?? Is this some kind of doublespeak?
So, let me see if I follow.
If it is a 3W LED, to determine what resistor to put in series with it if you want to run it at it’s maximum rated power from +5vdc, then do the following? (This assumes you won’t be using a PicoBuck modified to run 700mA.)
3W = .700* E, 3W/.7A= 4.3v across the LED, that leaves .7 v across the resistor.
.7v/.7A = 1 ohm, correct?
I’m wondering the same thing as “Member #466922”. How can you market this as a 3W LED? Even if we use the upper limit of Vf at 2.4v, it’s impossible to get 3W at only 700mA. It only works out to be 1.68W. So Sparkfun, what’s up with that? Are we missing something?
News - Your June Caption Contest
about a year ago
Announcing SFE’s new “Super Product” line. Our first two offerings come in Chocolate and Silicon.
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about 2 years ago
“This step requires the #85 Sonic Screwdriver….”
about 2 years ago
Photo contest needed! You using your S.H.O.V.E.L out in the wild. Remember, is more than just a tool for loading fuel into your system.
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