How to protect a microcontroller on a high voltage PSU

[msalko]

Hello,
I'm building a high voltage power supply, and so far i had problems with high voltage "creeping" into my microcontroller, which causes it to restart.

What I'm building is essentially a l293d connected to a transformer and an MCU  , i know how bad this sounds, buuut i still want to try it.

My question is what is the best practice to isolate the rails of the MCU and the l293d, I'm looking mostly for advice for what to do, since i can't get any measurements on it. (I don't have an oscilloscope)

I think my problem is the common ground, or the common 5v between the logic part of l293d and MCU, or the crystal being close to pins connected to l293d.
I also have this feeling that the reverse diodes in the l293d might not be good for protecting from reverse voltage on a high voltage powersupply.

[danadak]

Grounding practices, see -

https://www.dropbox.com/s/ruaf9booe17jk8n/PCB%20Layout.zip?dl=0


http://www.st.com/content/ccc/resource/technical/document/application_note/f7/f4/51/8d/a1/c5/47/8e/DM00182773.pdf/files/DM00182773.pdf/jcr:content/translations/en.DM00182773.pdf


Look at input pins terminated by high z loads, they are subject to C coupled pickup.


Lead/cable dressing/shielding....

If you don't have a scope, but have a PC (limited, will not be able to see high speed
transients, but still somewhat useful) -


You can start with a PC sound card based scope for free. Will give you basically
audio range scope, spectrum analyzer, and function generator all using your
PC sound card.


https://www.zeitnitz.eu/scope_en


http://www.zelscope.com/


http://www.ledametrix.com/oscope/


http://www.virtins.com/downloads.shtml


But first build a simple circuit to protect sound card inputs so you do not
ruin from transients, overvoltage. Google "protect sound card input".


For example   http://makezine.com/projects/sound-card-oscilloscope/


Sound card impedance bridge -


http://www.marucchi.it/ZRLC_web/ZRLC/Steber_An_LMS_Impedance_Bridge.pdf


http://www.sillanumsoft.org/ZRLC.htm


Regards, Dana.