re help with ultra long timing wellison kuhub cc ukans edu writes i have a project that was drooped in my lap that is somewhat a pain to design what i am looking for is a stable ultra long solid state timer what they want to do is to place this thing on the antartic ice shelf and measure the amount of snow fall over a period of six weeks every two weeks they want to trip a selonoid to discharge different colored pellets by gas pressure out across the snow then by digging down into the snow the snow fall amount can be measured as they come to the different color pellets the problem is trying to build a timer that would stand the cold degrees and a power source that wouldn t drain i have looked at the xr timers and the standard ne dual timers but thier temp specs won t go that low also two weeks equates to seconds per firing which means one big timing cap i have found farad yes farad caps that have a working voltage of volts and are small in size why are you fooling around with analog for this job a single chip micro and a crystal will do the job reliably and easily an only costs about that and a crystal and you re in business embed the whole thing in a foam insulated blanket power it from a solar cell use the excess power to heat the assembly during the day and rely on the insulation to hold the heat during darkness if you don t want to try thermal management contact someone like icl and have them cut you a special low temperature crystal it ll cost at most if you use a single chip micro you re looking at a parts count of maybe a processor a crystal two caps on the crystal a power fet to fire the solenoid a flyback diode and a battery this is fewer parts than you can build an analog timer for and is infinitely more reliable add a power zener diode for heat and a solar cell and the parts count screams up to pd assemblers are available for all the common single chip micros this application is so trivial you could even look up the op codes in the programmer s guide and create the binary with a hex editor john john de armond wd oqc interested in high performance mobility performance engineering magazine tm interested in high tech and computers marietta ga send ur snail mail address to jgd dixie com perform dixie com for a free sample mag need usenet public access in atlanta write me for info on dixie com
