Years ago I had a similar problem on a car. The culprit was a ground loop. A current surge induced some voltage=20 in the ground wire. Mark Jordan On 28-Oct-14 15:20, Neil wrote: > Which is why I ask. Yes, I do know about load dump, spikes, etc, and > the circuit I've been using with mostly small caps was done to reduce > the board size, and I had another engineer work that out. I've used this > circuit in several other PIC-based products and the EEPROM does not get > corrupted, but those are mostly cars. This truck (18-wheeler) is > obviously different. > > The circuit IS powered from constant power as it's recording some data > when the vehicle is off. It does detect power on to get out of > low-power mode. I measured the voltage (oscilloscope) at startup on > this vehicle and saw it come down to just under 10V. Sure, that may > vary in other situations, but I guess my assumption here is that the > brown-out protection and other mechanisms on the PIC should have worked > as designed (maybe a bad thing for me to do) to prevent corruption. > > Actually, on another circuit done some years ago the device did lose > EEPROM data occasionally, but enabling the brownout protection resolved > that. Thousands of units since then has not had the issue anymore. On > that one, there is no space left for any capacitor, but on this one now, > I can add a small cap, and I do have pads on the board for it in case it > was needed. Several farads seems way overkill though. I was thinking > more of an RLC filter to help clean things up. > > The issue currently is that I don't have easy access to the truck > anymore, so I can try/test things, so I'm going to have to work out some > sort of power source that can simulate the spikes perhaps. > > -Neil. > > > > On 10/28/2014 11:14 AM, Jean-Paul Louis wrote: >> Neil, >> By your last few comments, I am fairly sure that you are not familiar at= all with automotive electronics. >> You need to make sure that your circuit is not powered directly from the= battery, but from a power line that is disconnected when the engine starts= .. If not, you will have to face a huge voltage drop when the engine starts,= and the voltage will most likely goes down under 6 Volts, so you circuit w= ill be in a brown-out condition, hence the EPROM data corruption. >> If the power consumption is low, you should use a very large capacitor (= several Farads) to keep the voltage on while cranking the engine. >> >> my $0.02, >> Jean-Paul >> AC9GH >> Ex Automotive Engineer >> >> >> >> On Oct 28, 2014, at 12:54 AM, IVP wrote: >> >>>> I have verified that it's properly chassis grounded. Wires are >>>> unfortunately quite long, so I will have to look into protecting it. >>> Might there be a case for Schottky(s) etc on the 0V line (to V+) as >>> well as the measures on V+ ? To some degree the current events >>> on 0V will be concommitant with what's happening on V+ >>> >>> The very worst thing I ever made, as far as EMF is concerned, was >>> a butane igniter which used a PIC, HT supply and a spark plug. When >>> that thing went off it was noise city. Spikes were everywhere, both >>> through wiring and the air, really made a mess of the PIC's operation. >>> >>> Took a whole day experimenting with caps, diodes, resistors, chokes, >>> and shields (both case and cable) to sort it out. Far worse than any >>> car circuit I've filtered, although it didn't suffer from major >>> low-frequency V+ or 0V excursions due to the load switching often >>> experienced in automotive circuits >>> >>> Joe >>> >>> >>> >>> ----- >>> No virus found in this message. >>> Checked by AVG - www.avg.com >>> Version: 2015.0.5315 / Virus Database: 4189/8464 - Release Date: 10/27/= 14 >>> >>> --=20 >>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >>> View/change your membership options at >>> http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .