Neil, By your last few comments, I am fairly sure that you are not familiar at al= l with automotive electronics. You need to make sure that your circuit is not powered directly from the ba= ttery, but from a power line that is disconnected when the engine starts. I= f not, you will have to face a huge voltage drop when the engine starts, an= d the voltage will most likely goes down under 6 Volts, so you circuit will= be in a brown-out condition, hence the EPROM data corruption.=20 If the power consumption is low, you should use a very large capacitor (sev= eral 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. >=20 > 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+ >=20 > 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. >=20 > 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=20 > low-frequency V+ or 0V excursions due to the load switching often > experienced in automotive circuits >=20 > Joe=20 >=20 >=20 >=20 > ----- > 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 > --=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 .