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Embedded System in Noisy Environment

R

Rich

Jan 1, 1970
0
We've developed a Microcontroller System for automotive use with few
sensors and a solenoid valve control output via a Relay.
We've found these valves resets the microntroller used (ATmega128) when
opening or closing and partially solve the problem with a diode in
parallel of the solenoid.
Moreover, in seldom cases the progam resets or loose it's variables
(counters) stored in eeprom.
Voltage regulation is based in a LM2574 switcher. We have not
implemented further filtering circuits and our housing is made of
aluminum.
In my understanding we need some EMI shielding, or power line filters
to avoid the reset problem.
Any advise is appreciated.

Rich
 
J

Joerg

Jan 1, 1970
0
Hello Rich,

This could have a lot of causes. Besides reviewing the grounding you'd
have to measure VCC at various places, then measure whether any sensor
input spikes into the processor's substrate diodes etc. But this is
easier said than done because you have to avoid creating a ground loop
with the scope. If you try this yourself make sure to do "sanity
checks", for example touching ground with the probe tip and verifying
that no spike is seen while doing that.

If you aren't familiar with EMI I suggest to hire a consultant to help you.

Regards, Joerg
 
S

Spehro Pefhany

Jan 1, 1970
0
We've developed a Microcontroller System for automotive use with few
sensors and a solenoid valve control output via a Relay.
We've found these valves resets the microntroller used (ATmega128) when
opening or closing and partially solve the problem with a diode in
parallel of the solenoid.
Moreover, in seldom cases the progam resets or loose it's variables
(counters) stored in eeprom.
Voltage regulation is based in a LM2574 switcher. We have not
implemented further filtering circuits and our housing is made of
aluminum.
In my understanding we need some EMI shielding, or power line filters
to avoid the reset problem.
Any advise is appreciated.

Rich

I doubt either of those will solve your problems, and if they do it
will only be by chance. It's really necessary to take a look at the
overall system to see where the problems might be coming from. At a
minimum you're likley going to require a new PCB layout, though it's
sometimes possible to band-aid a solution for a few units.


Best regards,
Spehro Pefhany
 
G

Genome

Jan 1, 1970
0
Rich said:
We've developed a Microcontroller System for automotive use with few
sensors and a solenoid valve control output via a Relay.
We've found these valves resets the microntroller used (ATmega128) when
opening or closing and partially solve the problem with a diode in
parallel of the solenoid.
Moreover, in seldom cases the progam resets or loose it's variables
(counters) stored in eeprom.
Voltage regulation is based in a LM2574 switcher. We have not
implemented further filtering circuits and our housing is made of
aluminum.
In my understanding we need some EMI shielding, or power line filters
to avoid the reset problem.
Any advise is appreciated.

Rich

Yes, I can't help you.

You see my name is God and, for some strange reason, I have never
experienced similar problems.

I gave up looking for jobs a while back after I was made redundant.

I went to quite a few interviews but the people always seemed to be
interested in problems similar to your own.

Unfortunately I don't have experience of them.

I think I fucked up somewhere.

DNA
 
G

Guy Macon

Jan 1, 1970
0
Rich said:
We've developed a Microcontroller System for automotive use with few
sensors and a solenoid valve control output via a Relay.
We've found these valves resets the microntroller used (ATmega128) when
opening or closing and partially solve the problem with a diode in
parallel of the solenoid.
Moreover, in seldom cases the progam resets or loose it's variables
(counters) stored in eeprom.
Voltage regulation is based in a LM2574 switcher. We have not
implemented further filtering circuits and our housing is made of
aluminum.
In my understanding we need some EMI shielding, or power line filters
to avoid the reset problem.
Any advise is appreciated.

Go to [ http://www.guymacon.com/SUN/INDEX.HTM ] and scroll down to
the section titled "Industrial washing machine control."
 
M

Mark

Jan 1, 1970
0
i agree with what guy said....

is the diode that is in prallel with the solenoid monted directly at
the solenoid.

I also find a 0.1 uF cap at the base to ground of the switching
transistor slows thing down a little to reduce spikes.

Mark
 
R

Rich

Jan 1, 1970
0
Guy Macon said:
Rich said:
We've developed a Microcontroller System for automotive use with few
sensors and a solenoid valve control output via a Relay.
We've found these valves resets the microntroller used (ATmega128) when
opening or closing and partially solve the problem with a diode in
parallel of the solenoid.
Moreover, in seldom cases the progam resets or loose it's variables
(counters) stored in eeprom.
Voltage regulation is based in a LM2574 switcher. We have not
implemented further filtering circuits and our housing is made of
aluminum.
In my understanding we need some EMI shielding, or power line filters
to avoid the reset problem.
Any advise is appreciated.

Go to [ http://www.guymacon.com/SUN/INDEX.HTM ] and scroll down to
the section titled "Industrial washing machine control."

Thank you all for your advice.
Guy's article is very illustrative of where the problem is. Moving
the diode from the board to the solenoid was tried in the past and
work. In order to avoid the user to place a diode at the solenoid we
soldered it on the board, but as you explain:

"Electrically it was the same circuit, but the +5VDC spike went from
30 volts to around half a volt. The collapsing magnetic field was
creating a current that recirculated through the diode, and the wiring
between the solenoid and the diode was acting like a big loop antenna,
broadcasting the spike into the electronics. By placing the diode on
the solenoid, the size of the loop was made much smaller"

Is it a possible solution to keep the diodes on the board, and enclose
it in a copper Faraday Cage?
 
S

Spehro Pefhany

Jan 1, 1970
0
Guy Macon said:
Rich said:
We've developed a Microcontroller System for automotive use with few
sensors and a solenoid valve control output via a Relay.
We've found these valves resets the microntroller used (ATmega128) when
opening or closing and partially solve the problem with a diode in
parallel of the solenoid.
Moreover, in seldom cases the progam resets or loose it's variables
(counters) stored in eeprom.
Voltage regulation is based in a LM2574 switcher. We have not
implemented further filtering circuits and our housing is made of
aluminum.
In my understanding we need some EMI shielding, or power line filters
to avoid the reset problem.
Any advise is appreciated.

Go to [ http://www.guymacon.com/SUN/INDEX.HTM ] and scroll down to
the section titled "Industrial washing machine control."

Thank you all for your advice.
Guy's article is very illustrative of where the problem is. Moving
the diode from the board to the solenoid was tried in the past and
work. In order to avoid the user to place a diode at the solenoid we
soldered it on the board, but as you explain:

"Electrically it was the same circuit, but the +5VDC spike went from
30 volts to around half a volt. The collapsing magnetic field was
creating a current that recirculated through the diode, and the wiring
between the solenoid and the diode was acting like a big loop antenna,
broadcasting the spike into the electronics. By placing the diode on
the solenoid, the size of the loop was made much smaller"

Is it a possible solution to keep the diodes on the board, and enclose
it in a copper Faraday Cage?

That may actually make it worse, because of coupling to the board.


Best regards,
Spehro Pefhany
 
F

Fred Bloggs

Jan 1, 1970
0
Rich said:
Guy Macon said:
Rich wrote:

We've developed a Microcontroller System for automotive use with few
sensors and a solenoid valve control output via a Relay.
We've found these valves resets the microntroller used (ATmega128) when
opening or closing and partially solve the problem with a diode in
parallel of the solenoid.
Moreover, in seldom cases the progam resets or loose it's variables
(counters) stored in eeprom.
Voltage regulation is based in a LM2574 switcher. We have not
implemented further filtering circuits and our housing is made of
aluminum.
In my understanding we need some EMI shielding, or power line filters
to avoid the reset problem.
Any advise is appreciated.

Go to [ http://www.guymacon.com/SUN/INDEX.HTM ] and scroll down to
the section titled "Industrial washing machine control."


Thank you all for your advice.
Guy's article is very illustrative of where the problem is. Moving
the diode from the board to the solenoid was tried in the past and
work. In order to avoid the user to place a diode at the solenoid we
soldered it on the board, but as you explain:

"Electrically it was the same circuit, but the +5VDC spike went from
30 volts to around half a volt. The collapsing magnetic field was
creating a current that recirculated through the diode, and the wiring
between the solenoid and the diode was acting like a big loop antenna,
broadcasting the spike into the electronics. By placing the diode on
the solenoid, the size of the loop was made much smaller"

Is it a possible solution to keep the diodes on the board, and enclose
it in a copper Faraday Cage?

Is your problem that the solenoid is case GND'ed so that it is not
possible to use twisted pair power lines to it? And the solenoid is
switched in/out by a relay?- That creates a helluva mess with relay
bounce of power to the solenoid which can be on the order of solenoid
current rise/fall time.
 
N

Nico Coesel

Jan 1, 1970
0
Rich said:
We've developed a Microcontroller System for automotive use with few
sensors and a solenoid valve control output via a Relay.
We've found these valves resets the microntroller used (ATmega128) when
opening or closing and partially solve the problem with a diode in
parallel of the solenoid.
Moreover, in seldom cases the progam resets or loose it's variables
(counters) stored in eeprom.
Voltage regulation is based in a LM2574 switcher. We have not
implemented further filtering circuits and our housing is made of
aluminum.
In my understanding we need some EMI shielding, or power line filters
to avoid the reset problem.
Any advise is appreciated.

I always power relays from a filtered power supply (using a diode,
resistor and capacitor). This prevents spikes going back into the
circuit. Also, a switcher may not like the sudden extra current drawn
by the solenoids. The capacitor will help to overcome this.
 
R

Rich

Jan 1, 1970
0
Solenoid is about 4-5 feet from the uController system. Yes, solenoid
case is grounded to the truck. The other line goes to a relay in the uC
system wich switch 12VDC from the truck battery.
We use an optocupler between the uController and relay to drive the
solenoid.
I found some systems using Pi-Networks to filter power lines to the
system and an excellent AN at Littlefuse named
AN9312 - Suppression of Transients in an Automotive Environment.
http://www.littelfuse.com/cgi-bin/r.cgi/know_file_detail.html?LFSESSION=yoMURlJITi&FilebaseID=91
We'll implement these devices to the system field test and show the
results in the group during in the next days.
 
R

Rich

Jan 1, 1970
0
Rich ha escrito:
We've developed a Microcontroller System for automotive use with few
sensors and a solenoid valve control output via a Relay.
We've found these valves resets the microntroller used (ATmega128) when
opening or closing and partially solve the problem with a diode in
parallel of the solenoid.
Moreover, in seldom cases the progam resets or loose it's variables
(counters) stored in eeprom.
Voltage regulation is based in a LM2574 switcher. We have not
implemented further filtering circuits and our housing is made of
aluminum.
In my understanding we need some EMI shielding, or power line filters
to avoid the reset problem.
Any advise is appreciated.

Rich

We added a Pi-Network at the voultage input and the problem was solved.
 
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