[En-Nut-Discussion] Strange reset behavio (sligthly OT)

[Alexander Baranov]

IMHO, I'd rather stop these R-L-C circuits investigations and implement
external reset monitor. I use Dallas DS1232. You never know what kind of
noise meets you in your next building. I design building management systems
too.
Good luck, Alexander.
----- Original Message ----- 
From: "Ole Reinhardt" <ole.reinhardt at kernelconcepts.de>
To: "Ethernut User Chat (English)" <en-nut-discussion at egnite.de>
Sent: Friday, January 21, 2005 5:14 AM
Subject: [En-Nut-Discussion] Strange reset behavio (sligthly OT)


> Hi all,
>
> Sorry for asking a question a bit out of topic.
>
> I'm just building a complex system (automatical test engine for
> automobile parts) that consists of about 12 µC Boards running NutOS. All
> of these boards are connected by a CAN bus (SJA1000 connected to the
> ATMega128) to eachother.
>
> The main power is switched on by a relais. This relais is chattering?
> (in german: "das Relais prellt"). So without any precautions there a lot
> of transients on the main power line for about 2 ms after switch on of
> the mainpower.
>
> My problem: Some of my boards does not reset properly. I don't have a
> reset controller (like MAX811) or something similar. Ther's ony a R/C
> combination (C = 100nF, R = 100kOhm) to generate a reset signal.
>
> Like this:
>
>          -------              |  |
> VCC -----|  R1 |-----+--------|  |------- GND
>          -------     |        |  |
>                      |
>                      |         C1
>                   /reset
>
> My first consideration was that the transients on the main-power prevent
> the boards from booting properly. So I build a L/C combination to block
> these transients:
>
> Power supply / relais                       Backplane / Boards
>
>         L1          C1
> + ---/\/\/\/\-------+-------------------------------- +5V
>                     |
>                     |
>                  =======
>
>                  -------
>                     |
>                     |
> - ------------------+-------------------------------- GND
>
> L = between 50µH and 100µH (from my hobby box)
> C = elko, 470µF
>
> Everything now seems alright. Main Power rises a bit above 5V and then
> goes down to 5V, but no more fast transients. Beside this nothing was
> better. Some boards still does not boot properly.
>
> No I changed the above circuit a bit (in my eyes nonsene, because I now
> have a L / C oscilator and it should make the transients even worse):
>
> Power supply / relais                       Backplane / Boards
>
> + ------------------+--------------------------------- +5V
>                     |
>                     \
>                     /
>                     \
>                     /      L1
>                     \
>                     /
>                     |
>                     |
>                  =======
>
>                  -------   C1
>                     |
>                     |
> - ------------------+-------------------------------- GND
>
> WOW! Now it works. But as I supposed the transients on the main power
> are even worse and overshooting (undershoting) the 5V a lot.
>
> In my eyes this works by accident, but I'm searching a REAL solution.
>
> Is there anybody who can give me an advise what could be wrong?
>
> Regards,
>
> Ole Reinhardt
>
>
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