Smoking arduino by n00b

At one of my first attempts of building a circuit with an arduino using 12v DC I made a mistake connecting it and drew some smoke...
I can still upload programs, but I cant switch between HIGH and LOW properly.
For instance with a LED, it will be always HIGH, but with different strengths.
In my project in need to switch some 12V DC on and off.
Would like to confirm that i need a new board.
Thanks for your time.

It sounds like you have blown the output pin. You could try pins that were not connected to 12 volts to see if they work. But getting yourself a new controller chip would be a good idea

thanks for the quick reply.
I am using the vin pin, there is no problem with getting power (tested on LED series), but i would like to switch it on and off with a relay.
Judging by how the LED of pin 13 behaves with the blink sketch it would be possible. If i connect the vin pin and gnd to a relay it just clicks once and thats it.

There is a diagram in the playground that shows how to connect a relay: Arduino Playground - HomePage

If I just test the relay, connecting the positive and the negative, running the "blink" sketch. The relay "clicks" once, and doesn't toggles, as far as I understand he should be opening and closing with the "blink" sketch.

How have you connected the relay to the Arduino? To which pins? Are you using a driver transistor?

while running blink.
I tried to connect a transistor to through the vin pin, it just stays on all the time

or i tried through the 13 pin and a 5v relay, and it turns on once when connected and thats it.

Thanks for your time.

You can't connect a relay directly to an arduino, there is not enough power to drive it. You need to use a transistor and resistor as well.

Look at this link:- Motors 1

Halfway down the page there is a relay circuit.

Sorry for the delay between posts, but I decided to get all code done in my app, leaving what I don't know for last.
I am using a 12dc air pump and some paralel series of LEDs, they work fine when just connected to VIN and GND with 12v adaptor. Would like to switch them on/off.
I have a relay , built a circuit with it as seen above and fried the board. Should I just use a transistor (got bc546 transistor), I think it might be more strait forward?

Grumpy mike gave you the best answer in the link he posted. You DO need a transistor between the Arduino and the relay if it is anything but the tiniest of relays. (I really mean tiny)

Your relay has the potential of even giving the BC546 a little strain if it is a low impedance kind... ~75 Ohms read at the coil. You should know that before you start attaching things.

The transistor base should have a resistor (~1K or more) connecting to the Arduino pin. The relay should have a protection diode across the coil. This is the best way to connect a relay and eliminate the risk of releasing the magic smoke that makes the Arduino work.

Could I use a transistor only?
Or I am missing the point here.
See I had a little tutorial with an aquitence, and he explained that I can ether use a Relay OR a Transistor when using 12v.
So i am a bit confused... and a board down..

There should be no “OR”. You use a transistor WITH a relay. If you use just a transistor and LEDS, you then need to know how many LEDs how much current each draws and add it up. If you have 10 LEDS and a BC547… you could break the BC547 too.

Here is the thing. Making the relay engage equals WORK. How much work depends on how much current (power) the relay demands from the circuit when engaged.

The arduino is a complex device and it has limits on how much current (power) it can supply when it is asked to do work.

The transistor is a HELPER device. When the Arduino brings the PIN HIGH to the base of the transistor, it looks like a tiny load for it to bear. The transistor then is told to do work, it swithes to an “current flowing” state and it then does the work of making the relay energize.

So, you need a transistor to HELP drive the relay and to keep Arduino working safely.

This diagram Arduino Playground - HomePage
shows how to use 5v with a relay. How about if i would like to use 12v ? same thing different pin?

Where it says "RELAY POWER +" you apply 12V. This the ONLY place you apply 12 volts. The transistor provides voltage level isolation. The 12V is only to energize the relay coil. The transistor, when "turned on", completes the circuit and energizes the relay coil by supplying a connection to GND.

NOTE: The 12V RELAY POWER GND and the Arduino GND are tied together. It's in the diagram.

Pardon my ignorance.
In the diagram, what does the drawing between the the collector and relay power stands for?
And where in this fits the device that I want to control, for instance the LEDs?

The device, drawn as a box with a line through it, is the relay coil.

The switch linked with a dotted line, labelled s1, k1,01, p1 are the relay contacts. The leds are connected using the relay contacts.

The diode across the relay coil is important and will avoid the transistor blowing when the relay is turned off.

I re-drew the relay diagram a little while back. You may find it easier to read:


I'm afraid I am not there yet...
This is what I have.

Arduino gnd -> emitter
Arduino pin2 -> 1K resistor > base
collector -> relay coil
Arduino 12v -> relay coil

Now I am getting confused, how to connect the LEDs to this. I am inclined to connect the LEDs circuit gnd to the emitter but not sure where to connect the positive;
This is the relay I am using

I understand where the coil is, but to which of the remaining 6 pins i connect the LEDs positive to? If at all...

Thanks for your time!

Thank you guys, I got it working. Maybe this image will help some one