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Copper Area/ Resistors?
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trevor_rau 8 years ago
This is the first board I've ever designed and I've seen a lot of boards have complicated copper areas and mine has none. I was wondering if someone could help me out with my design if i need to change anything. Also anybody educated in LEDS could you help me. From my design I have 11 SMD green LEDs in parallel I think. Most green LEDs have a forward voltage of 2.4V. Im powering my circuit with a 1220 coin cell which is 3V. Do i need a resistor after my switch to not kill my LEDs. Thank you.![enter image description here][1] [1]: https://easyeda.com/export_YyGz5ZTbt/E-PCB.png?type=3&width=0&pageSet=merged&exportColour=0&exportListStr=1,2,3,4&mirrorListStr=&isAssemblyDrawings=0&version=3.6.7&_t=1468456243597
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trevor_rau 8 years ago
The board is the letter E which is turned on by a SPST switch. Ideally set up as a necklace with the hole.
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support 8 years ago
Your image is private, we can't see it.
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trevor_rau 8 years ago
Fixed?@support
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dillon 8 years ago
https://easyeda.com/Doc/Tutorial/PCB.htm#Copper-Area You need to set the copper's net right ![enter image description here][1] [1]: /editor/20160714/578725ff742ec.png
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andyfierman 8 years ago
@Trevor, Welcome to EasyEDA. * It is not a good idea to try to drive LEDs without some resistance in series with them. For guidance on the care and feeding of LEDs, please see: https://easyeda.com/andyfierman/LEDs_must_have_series_resistors-OoGYgCK2k :)
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trevor_rau 8 years ago
@dillon Thank you for the help. Like you I did the net D11_- like you have done and then on the bottom layer I did the same thing but for D7_+. Does that sound correct or do I not need the bottom one? I don't really understand the tutorial they provide. Thank you very much
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trevor_rau 8 years ago
@andyfierman So according to your article it says to put a resistor with each led. What if I put one resistor right after the switch, that would limit the current to all the LEDs wouldnt it? since the forward voltage and source are relatively close a small like 3.3 ohm might work right? Sorry if you explained this in your article it was a little tough for me to fully grasp what was written. Thank you in advance.
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andyfierman 8 years ago
`What if I put one resistor right after the switch, that would limit the current to all the LEDs wouldnt it? since the forward voltage and source are relatively close a small like 3.3 ohm might work right?` That's not a good idea because it does nothing to even out the current sharing across all the diodes. The resistor passes the total current for all the LEDs ao it has to be small. That means that it also does very little to reduce the change in current through it vs. supply voltage, which the another reason for using resistors in series with LEDs. What you propose is the centre pair of LEDs with the big red cross through it in my diagram. So, no. Save yourself a lot of wasted time and dodgy brightness and battery life and just fit resistors in series with each LED. BTW if you are using blue and white LEDs (and some of the more exotic green ones) then 3V is not enough to get any relaible illumination out of them because the forward drop of them is about 3.6V anyway. 3V is OK for the red, green and yellow LEDs with approximately 2V forward drops but for the blue, white and high brightness green LEDs you'll need 4.5V to get anywhere near a reasonably reproducable, stable brightness from ne pcb to the next and across battery life.
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