Embedded System in Noisy Environment

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

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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

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

Go to [

] 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

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"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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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.

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.

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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.

We'll implement these devices to the system field test and show the results in the group during in the next days.

Rich ha escrito:

when

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