PWM Dimming 140 mA (7pcs x 20mA each) won’t work on FLORA ?

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GJGeist
 
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PWM Dimming 140 mA (7pcs x 20mA each) won’t work on FLORA ?

Post by GJGeist »

Hi, I have 7 parallel LED's that I am trying to dim using the PWM pins. I need a board that will fit within a 3"x2"x0.3" box, So i picked the FLORA.

The problem is that I can’t seem to get the full brightness out of the FLORA.

For reference, I have hooked 2 LEDS (in parallel) to a separate 3.3v source, the LEDs are very bright. My meter says they are pulling around 40mA from the power supply.

But when I hook the same LED's between Pin D9 and GND of the FLORA, the LED's only seem to get 8mA.

I was planning on putting a pair of LEDs on each pin, but it looks like they will only be 1/4 the brightness.

The advertising says: "The FLORA has an onboard 3.3v 150mA regulator." I think I also read somewhere that each pin of the Flora could put out only like 40 mA each.

My questions:

Am I doing something wrong?

Should the LED's be in series ?

Do I need some kind of LED driver instead?
What about this TLS59711 driver. It seems to let you 60 ma per channel !!!
https://www.adafruit.com/products/1455

What about these boards, would they work for me ? They are tiny and claim that each pin can handle 40-50mA:
http://arduino.cc/en/Main/ArduinoBoardMicro
http://arduino.cc/en/Main/ArduinoBoardLilyPadUSB

-Greg


LED link: http://www.luckylight.cn/UploadFiles/V020W-W6-1E-RL.pdf

=================================
The code I’m using is basically the same as the Fade.ino example
(With the DIM_VALUE of 0-254)

void setup() {
pinMode(9, OUTPUT);
}

void loop() {
analogWrite(9,DIM_VALUE);
}

==================================
Last edited by GJGeist on Mon Jul 28, 2014 9:33 am, edited 1 time in total.

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adafruit_support_bill
 
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Joined: Sat Feb 07, 2009 10:11 am

Re: PWM Dimming 140 mA (7pcs x 20mA each) won’t work on FLOR

Post by adafruit_support_bill »

40mA is the absolute maximum rating for a Flora pin. Overloading the pin can damage it.

To drive 7 leds in parallel, you need something capable of handling the current (7x20mA = 140mA) You can use the PWM pin to drive a transistor that will switch the current: https://www.adafruit.com/product/756

Another option is to use a dedicated PWM led driver: https://www.adafruit.com/products/1455
That will let you control up to 12 sets of leds individually.

GJGeist
 
Posts: 3
Joined: Sun Jul 27, 2014 11:47 pm

Re: PWM Dimming 140 mA (7pcs x 20mA each) won’t work on FLOR

Post by GJGeist »

Bill:
So if each pin can handle 40 mA, shouldn't I be able to drive one 20 mA LED at full power ? With one LED all I can get the FLORA to provide is around 8 mA.
-Greg

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adafruit_support_bill
 
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Joined: Sat Feb 07, 2009 10:11 am

Re: PWM Dimming 140 mA (7pcs x 20mA each) won’t work on FLOR

Post by adafruit_support_bill »

What is the forward voltage of the LED you are using and how do you have it connected?

GJGeist
 
Posts: 3
Joined: Sun Jul 27, 2014 11:47 pm

Re: PWM Dimming 140 mA (7pcs x 20mA each) won’t work on FLOR

Post by GJGeist »

Forward Voltage:
Min 2.8v
Typ 33.4v
Max 3.8v
If =20mA

Im hooking the LED between Pins GND and D9 of the FLORA.

LED link: http://www.luckylight.cn/UploadFiles/V020W-W6-1E-RL.pdf

=================================
The code I’m using is basically the same as the Fade.ino example
(With the DIM_VALUE of 0-254)

void setup() {
pinMode(9, OUTPUT);
}

void loop() {
analogWrite(9,DIM_VALUE);
}

==================================

User avatar
adafruit_support_bill
 
Posts: 88088
Joined: Sat Feb 07, 2009 10:11 am

Re: PWM Dimming 140 mA (7pcs x 20mA each) won’t work on FLOR

Post by adafruit_support_bill »

See the forward current vs forward voltage chart on the top-right of page 5. The Flora pins will output at most 3.3v, so you would never get 20mA.

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