digital pins don't always work properly

Alright, I’m working on a quite extensive project, for my first arduino project. Tough I’m familiar with C coding. I’m doing something that switches 8 high powered automotive leds to the sound of a bass drum in a few different patterns. Right now I’m just prototyping it, so I’m using standard leds.

So I was wiring up a switch to enable the user to choose if he’s plugging 4 or 8 lights and I probably shorted something. I had connected the +5v, digitalPin 2 and the ground to my switch but forgot to put a tie down resistor. So when I switched it, my computer gave me a warning that the usb port was drawing too much power.

But now, the leds connected to digitalPin 11 and 12 are dimmed. It’s not the leds as they work on other pins.

Good thing I waited to post, I commented serialPrints and they started working properly. But now I’m having trouble with pins 6 and 7, yet 5 works. I’m not sure if they worked before as I had nothing connected before. I’m currently trying it out with the blink sketch (changing ledPin to 7, 6 and 5) so I’d be very surprised if it was a problem with the sketch. I also have nothing else connected or touchubg the board at the moment. Mind you, this time pin 6 and 7 are not dimmed, they just don’t work at all.

Is there something special about pin 6 and 7 that I’m missing out on ? I don’t mind connecting to say pin 5 and 4 but it seams I’m getting reliability issues here.

EDIT
After some pocking around with the multimeter, turns out when either pin 6 or 7 is on, both out .7v and when they are off they still output .2v, contrarily to the stable 0 of the other pins.

So I was wiring up a switch to enable the user to choose if he’s plugging 4 or 8 lights and I probably shorted something. I had connected the +5v, digitalPin 2 and the ground to my switch but forgot to put a tie down resistor. So when I switched it, my computer gave me a warning that the usb port was drawing too much power.

As described that could draw too much power but i don’t see it hurting the arduino.

But now, the leds connected to digitalPin 11 and 12 are dimmed. It’s not the leds as they work on other pins.
…I commented serialPrints and they started working properly. But now I’m having trouble with pins 6 and 7, yet 5 works. I’m not sure if they worked before as I had nothing connected before. I’m currently trying it out with the blink sketch (changing ledPin to 7, 6 and 5) so I’d be very surprised if it was a problem with the sketch. I also have nothing else connected or touchubg the board at the moment. Mind you, this time pin 6 and 7 are not dimmed, they just don’t work at all.

Is there something special about pin 6 and 7 that I’m missing out on ? I don’t mind connecting to say pin 5 and 4 but it seams I’m getting reliability issues here.

So this has moved around a lot.
What kind of board is it, did you buy it assembled or as a kit and which pins work/dont?

After some pocking around with the multimeter, turns out when either pin 6 or 7 is on, both out .7v and when they are off they still output .2v, contrarily to the stable 0 of the other pins.

This sounds specifically like a hardware short of both pins to something but the whole business of pins 11 & 12 and the serial don’t fit with that.

As described that could draw too much power but i don’t see it hurting the arduino.

The Specifications for the ATmega controller chip used on Arduino boards warn not to draw more than 40ma from a pin. They are not protected from over-current and you can damage the pins if you short them out.

The Specifications for the ATmega controller chip used on Arduino boards warn not to draw more than 40ma from a pin. They are not protected from over-current and you can damage the pins if you short them out.

The way I read it he had shorted +V, a pin, and ground. It wouldn’t seem the arduino could source much current with the +V shorted to ground.

I guess your point is though that it is possible to damage individual pins without borking the whole device.

It’s an Arduino Duemilanove with an atmega 328 I recently bought from robotshop.

All the digital pins work except for 6 and 7, so that hasn’t changed. Odd thing is that I had shorted on pin 2 and that one still works.

I had a SPDT switch, 5v on the pole, ground on one side and pin 2 on the other.

I’ll later try swapping the ATmega chip with the one on my friend’s arduino to see if the problem is with the board or the chip. If it turns out the problem is with the board, it should be very unlikely the damage was done by shorting pin 2, right ?

I had a SPDT switch, 5v on the pole, ground on one side and pin 2 on the other.

So you could connect 5v to ground or 5v to pin 2? I don’t see either of those hurting the chip. I would have a darned good look at the solder and traces around pins 6&7 (pins 12 & 13 on the AVR chip itself).

Putting your chip into a known good board should tell the tale. They’re not expensive if you need to replace it.

Thanks for the feedback, I had a feeling that I wasn’t doing anything too bad. I’m not sure how the message I got works, it’s possibly my two usb ports that were together drawing 500ma when I flicked the switch.

Turns out the chip is the cause of the malfunction. Not too bad, I was already planning to buy a few to put them in projects that don’t need the whole arduino board. I still am kind of bummed I got a faulty chip, I wanted to get that project out as soon as possible. Oh well, I’ll have one to try crazy things on haha.

It’s good that you got it working, but I highly doubt that it’s the chip that was at fault. If you had an over current message on the computer, it’s more likely that you did in fact have a short that damaged the chip. Consider it the cost of learning :slight_smile: