HI MY mbed doesnt turn on anymore :S. I bealive it was due to shortcircuit, if so, or if u have other options of what could have happened to my mbed, I would like to know how to fix it :S.

It doesn turn on neither usb connected nor Power supply connected.

What makes you think it doesn't work anymore? Dit you already connect something to your mbed? If so deconnect everything and try again. Maybe fried your chip due to over voltage? What does your computer tells you when you power up your device with the usb cable? What have you done that could explain why your mbed refuses service? Does the blue led (power) comes alive when you connect?

If you want to get help here. Be more specific ...

Blue led doesnt turn on, I was building this circuit and suddenly mbed turned off. At this moment I connect it to my computer and doesnt turn on and is not detected(nothing in my pc appears). I measured 5v on usb terminals :S but it doesn turn on. Beside that, I noticed when I connect it to my power supply it is getting hotter :S.

OK nice drawing. but why don't you give resistance values? Have you read the lpc1768 datasheet or even the mbed technical sheet? Concerning max teminal output current? i think ( not going to search for it ) 25mA max per pin. 400mA max dissipation for the whole chip. What gets warm? The lpc? The voltage regulators? Do you always use an external power supply of is the 5V derived from the usb 5V that the mbed provides? ( not the smartest thing to do but should go fine for 1 relay ) If you use external supply. Have you coupled USB and power supply grounds together? VERY important !! Anyway. If the blue led stays dead. chances are 90% You somehow fried your chip. Due to over voltage ... Maybe other users can give there id's ...

there are the values. resistance coil is 220 ohms. The LD33-F013, LPC, every IC become hotter. sometimes I connected 4n25 led´s ground to p. supply ground :S being anode connected to 3.3v from mbed p6. Anyway,it seems I have to buy other one. ty.

To me it seems like you made a grounding fault. Ground of mbed usb schould ALWAYS be coupled to your power supply ground. Ground from opto schould not be coupled to the mbed ground. ( because it then loses his isolation function ) BTW why the opto? You don't need that part because the relay already gives you galvanic isolation ...

Anyway you killed your mbed i think.

Don't have to much time but i made you a quick paint drawing on how you should connect switching hardware to any mcu system. Do yourself a favor and leave the opto behind. Resistance values are guessed but certainly high enough to not kil lthe chip and low enough to actually do something. If you use it to trigger triacs or scr's. stuff like that you are right to use an opto. But when using relays you can leave that part away.

Bonne chanse they say en france ;)

I put opt in order to have more safety but as u can see I fried my mbed u.u. ty man I´ll take in count your circuit :).

Another fault that might have cost you 45€. you where building the circuit when your mbed suddenly stopped working ?? You should never start building external hw when your mbed is already connected to an unfinished circuit.

You should always finish it and test the working of your hardware with some wires directly from ground and Vcc. Measure it and check if it works like it's supposed to work before you connect your mbed !!! If you make a mistake you could blow up your inexpensive tor or other hardware instead of your costly mbed. So what ... you take a fresh one and continue with what your where doing. No harm done. You will learn from that mistake. Experience is the sum of all your mistakes ...

In my schematic you should see something like 5mA of current flowing trough the led and 3.3mA trough the base resistor of your transistor. You can safely measure such a small current directly with your multimeter. Any diehard electronic guy will tell you this is not done. you measure the resistance, the voltage across and you calculate the current. I know that! But i don't know you skill level in electronics so do as i say and measure any current < 90mA directly with the meter.

A transistor normally has @ least a B factor of 100 (A types). Normal used hand rule for a small signal tor in switching mode: Ib=1mA with will +/- result in an Ic switching current of minimum 100mA. I guess your relay needs 50mA to function properly? So you can change the 1K base in my schematic with 3K3. It is even better than 1K. if you would like 20mA for the led you could lower that R To 270 if you like. Total P tor(on) is Ic MAX 70mA * 0.4Vce = 28mW <= 100mW Ptor MAX. So you are in the safe zone and it will work perfect! No cooling required.

Keep in mind that you still are very lucky because usb ports are CC protected to 500mA as it's used as "high power" device. If this wasn't the case you could have damaged your computer. that is why your mbed doesn't get warm on usb and starts to heat up with an unprotected power supply who can deliver your Short circuit current!

Greets,

Tom