A20-olinuxino-micro 3.3V damaged

[vision]

Hi All,

can anyone tell why 3.3 V is damaged, and whether it can be repaired ?
I have the same problem like described here:

https://www.olimex.com/forum/index.php?topic=3122.0

I connected IO as follows:
- 8 LEDs at GPIO
- MCP3008 at spidev1.0 (3.3V supply)
- terminal at uart0 (cable F)

The board is powered with SY0612E.

Then i connected a relais circuit via an opto-coupler to a GPIO. The relais circuit was powered externally with 12 V. Common ground.
Seems that this destroyes the 3.3 V on the board.

Now i dont know what i did wrong.

Please tell me.

[JohnS]

Relays create very nasty voltage spikes and RFI/EMI.  What did you do about those?

John

[soenke]

If you had a optocoupler between the relais and the board there should not have happened anything exept that the optocoupler might fail because of the high currents a relais draws, but that depends on the optocoupler you used.
The common ground should not be a problem as long as you dont connect the 12V to the 3.3V at the same time

What voltage are you measuring now on the 3.3V test point?

[vision]

Hi JohnS, hi Soenke

@JohnS
I had a free wheel diode connected in parallel to the relais, and the relais was controlled by a transitor.

@soenke
Measurment is about 0.2x V. Think i have not accidental connected 12V to the 3.3V.

I ordered a new a20-olinuxino-micro because i have some good things working fine on this board.
Would be nice if i could control relais via GPIO.

But how to avoid to destroy another board ?

Thx for reply.

[soenke]

I use SSRs like the IXYS CPC1017 to control coil relais. With them there is no risk for wrong polarity on the output and 100mA should be enough for almost all relais.

[vision]

Hi soenke,

tnx for this hint.
Can you give me an example of how to use it ?

I have got a new board now, and hope not damage it any more.

[soenke]

GPIO --> 470Ohm Resistor --> SSR input --> GND
+24V (or the voltage needed for the relais) --> Resistor to limit current to e.g. 50mA --> SSR output --> Relais input --> GND