Which is why I ask. Yes, I do know about load dump, spikes, etc, and=20 the circuit I've been using with mostly small caps was done to reduce=20 the board size, and I had another engineer work that out. I've used this=20 circuit in several other PIC-based products and the EEPROM does not get=20 corrupted, but those are mostly cars. This truck (18-wheeler) is=20 obviously different. The circuit IS powered from constant power as it's recording some data=20 when the vehicle is off. It does detect power on to get out of=20 low-power mode. I measured the voltage (oscilloscope) at startup on=20 this vehicle and saw it come down to just under 10V. Sure, that may=20 vary in other situations, but I guess my assumption here is that the=20 brown-out protection and other mechanisms on the PIC should have worked=20 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=20 EEPROM data occasionally, but enabling the brownout protection resolved=20 that. Thousands of units since then has not had the issue anymore. On=20 that one, there is no space left for any capacitor, but on this one now,=20 I can add a small cap, and I do have pads on the board for it in case it=20 was needed. Several farads seems way overkill though. I was thinking=20 more of an RLC filter to help clean things up. The issue currently is that I don't have easy access to the truck=20 anymore, so I can try/test things, so I'm going to have to work out some=20 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 wi= ll be in a brown-out condition, hence the EPROM data corruption. > If the power consumption is low, you should use a very large capacitor (s= everal 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: 10/27/1= 4 >> >> --=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 .