PWM pin burnout? Any ideas why?

Development Tools IDE 1.x
1

I've been running a sketch nonstop on a arduino clone (Mondern Device BBB) for about 6 months now, 24 hours a day. It's part of an art installation and it basically just blinks a few leds and moves a servo once every few seconds.

I've found Pin 10 PWM has stopped working out of the blue. It's only load was a 5mm blue led which it faded up and down every 2 seconds (yes, I had a resistor on it XD).

I've adjusted the code and hooked up the led to an unused PWM pin but I'd love to know why the previous pin just failed like that after 6 months. Any ideas out there? Luckily this art installation was only a 40 minute drive from me but I'd be concerned about using any arduino in an installation on the other side of the country without knowing why this happened.

2

Hi,

I guess its possible that something in the environment shorted it at some point or that the resistor still allowed too large a current to flow which while not enough to blow the output transistors instantaneously was enough to kill them slowly.

Duane B

3

To build on DuaneB's intuition: How did you calculate the resistance needed for the LED, tatticus?

4

I just used the Adafruit iPhone app to calculate the resistor. Supply voltage = 5volts, forward voltage = 3.3, forward current 20ma which gave a resistor value of 85ohms and I used 100ohms.

I'm doubting it was shorted out, it was inside a clean project box but anything is possible I've learned.

There are actually two pwm pins with identical LEDs, resistors and code that ran for the same amount of time but only the one pin died on me.

5

tatticus:
I just used the Adafruit iPhone app to calculate the resistor. Supply voltage = 5volts, forward voltage = 3.3, forward current 20ma which gave a resistor value of 85ohms and I used 100ohms.

I'm doubting it was shorted out, it was inside a clean project box but anything is possible I've learned.

There are actually two pwm pins with identical LEDs, resistors and code that ran for the same amount of time but only the one pin died on me.

What is the part no. of the blue LED?

6

During construction did you do anything that might have caused damage to the pin? Damaged components don't always fail at the time of damage.

7

As for the part number it was just a cheapo LED bought in bulk on an eBay auction. More recently, for important projects I've been using what I assume are higher quality (judging by price alone) LEDs from Super Bright LEDs .com. Do you think a bottom dollar LED could have caused this?

I guess damage during construction could have also occurred. Maybe it's just what I'll tell myself to solve the mystery.