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Topic: Arduino freezes completely (Read 1 time) previous topic - next topic


i have been working on a project, where i read Temperatures and switch relays depending on the temperatures. The relays are switched via a Darlington Array(ULN2003, i also tried normal relay drivers before). I use 12V/10A relays. The 12Volt are fed to the circuit board via an extra plug and the arduino uses it via the Vin Pin( i have a jumper to disconnect it though).
I get random freezes, when i switch a relay that is turning on a 230Volt pump. The Watchdog timer realizes the freeze and restarts the sketch,but i have to unplug it from the power source and USB to get it working again( i guess the FTDI Chip hangs too?!).
In the Serial Monitor i get following output(each Line is a response to a ON/OFF command):
100 OK No Timeout
100 OK No Timeout
100 OK No Timeout
100 OK No Tim

So the serial communication suddenly stops...

I tried these things:
-Disconnected Arduino from 12Volt Power supply => no supply voltage noise problem(i am not sure about this one)
-switching another relay (that is further away) which switches the 230Volt => no EMF noise problem

I use the String library,but this would only hang the Arduino and not the FTDI chip i think?
I have no decoupling capacitors...could that be the reason for the freezes?

Any Idea is appreciated.
Thanks for your help,


Do you have snubber diodes across the relay coils?
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
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Dec 17, 2012, 01:53 pm Last Edit: Dec 17, 2012, 11:29 pm by alexaustria Reason: 1
i had them in my first design with the transistor relay driver but forgot them in the new design with the ULN 2003. I will add them but since the error also appeared in the first design, i dont think this is the problem, but i will doublecheck, maybe i soldered them the wrong way.

edit: diodes  didnt change anything, still random freezes

James C4S

I have no decoupling capacitors...could that be the reason for the freezes?

Certainly doesn't help the situation to not have them.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com


Dec 18, 2012, 03:02 am Last Edit: Dec 18, 2012, 03:03 am by be80be Reason: 1
I have had freezes like that the ADC and the serial use interrupts and both where happening at same time I guess  because I added a small delay between them and it fixed it  
But always use a cap on the uc power rails 

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