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Ezb And Leds

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I wish to control LEDs by EZB . I saw in a tutorial leds connected directly to digital outputs without current limiting resistors. The leds I'd use sink 70 mA at 3,3 V . I don't think EZB could withstand such currents ! EZB specs only say the pins are TTL compatible but don't say what's the allowable current (high and low level). What's the allowable current ? I'd add current limiting resistors if necessary. I'd be disappointed burning out my EZB controller.


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#2  

@leonardo46 The max current of the ezb4 digital pin is 10mAh (as per Jeremie)... Jeremie has also mentioned that each digital pin has a built in current limiting resistor... My under standing is a basic 3v run-of-the-mill LED can be plugged in directly to the ezb4's digital pin without a resistor of it's own... Saying that I can't speak for the LED that you have...

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#3  

@Leonardo,

Richard is correct.

  1. The micro-controller specs are 25 ma.

  2. EZB controllers have a resistor in serie (333 330 ohm) between the micro-controller pin and the digital pin.

If you look the pcb : (smd resistor green block) number 331 => (33 * 10^1 = 330 ohm)

For 3.3 v (digital output) you have:

I = V/R => I = 3.3 / 333 330=> I = 9.9 10 mA

So it's safe to drive the led without a resistor.

@Jeremie: Nice design !

*** Edited corrected after (post #15)

#4  

I do not believe it is safe for him to drive that LED. It draws 70 mA which is too much for the EZB. IT will burn out the channel it is plugged into.

From what I understand don't use an LED that draws more than 10 mA unless you use a switching transistor or something.

#5  

OK. So I can even short circuit the pin without the risk of damage. I can't use the 25 mA available, but it's good to have a built-in protection. My leds, @ 3.3 V , with a 330 ohms resistor in series, would draw only 4 mA (instead of 70 mA) making a weak light, but it could be enough. Thanks to Richard and PTP, who was more specific in solving my problem.

PRO
USA
#6  

@Perry_S

There are different types of Loads, leds are pretty specific.

There are two details: forward voltage and current

It's the forward current that determines the brightness of an LED

If you have 70 ma led, means that is the limit and the peak for brightness.

Summarize: 70 mA Led to an EZB pin (10 ma) => 1/7 of brightness. 20 ma Led to an EZB pin (10 ma) => 1/2 of brightness. 5 ma Led to an EZB pin (10 ma) => will damage the led

*** Edit: This is the simple mode (one variable = current) but there is another variable: led forward voltage.

PRO
USA
#7  

Part II: Led full details

EZB: Pin output: 3.3 v Pin resistor: 330 ohm

Led Details: Forward Voltage: 1.9 v Max Amps: 10 ma

I = V/R I = (3.3 - 1.9) / 330 => 0.52 mA 0.0042 A or 4.2 mA

So the current is 0.52 mA 0.0042 A or 4.2 mA

that's ok for a 10 mA led (half bright)

but it's not ok for a led with max 4 mA

1 mA = 0.001 A

*** Edited: Leonardo post #11 Changed the numbers, the formula is ok, the numbers way off:)

#8  

Perfect, PTP. You solved the question and provided great detail. It's useful for everybody. My tests confirm everything. By the way, how can I blink for some time the led ? EZB scripts don't have something like the "do" in basic.

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