Old Tom wrote:Quick one for Ole Joe; Do you know what the capacitance was for the Frontier crystals? I spent a rainy Sunday afternoon many months ago tracing out the oscillator circuits on Frontier boards (2005, 2006 & 2007) and they are quite unlike any other LED watch oscillator circuit so sticking any old 32768Hz crystal in there probably won't work.
We tried to get as many xtals that liked a load capacitance of around 11 - 12pf for both stability and power dissapation. The xtal manufactures yields ran from about 7pf - 15pf and they charged us accordingly for cherry picking the 11-12pf. We finally had to start buying what they produced to keep up with the demand from all the watch manfactures. That forced us to select the fixed capacitor in the oscillator circuit to load the xtal up correctly. A real pain in the behind to say the least. Assemblers on the production line would often pick the wrong cap value or mix values for the given xtal and the modules would not tune to within the +/- 3ppm value of the 32.768KHz. Re-work mania, purge the production line of all fixed caps and issue new ones until they would do it again.What fun days those were, brings back many happy memories. I've had a few of the modules I have in my inventory fail to tune within specs and had to go chasing cap values to get them within spec. Luckily I've a fairly large inventory of chip caps, trimmers and crystals to select from. Most any xtal that I've got will make the oscillator play, but pulling them into spec somtimes takes a couple of guesses to find the correct value for the fixed cap.
16 Feb 2012, 20:06
