re help with ultra long timing in article apr kuhub cc ukans edu 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 but again the time of discharge at or lower degrees isn t linear i was thinking of using several timers chained together to fire the selonid at the end of the timing period but that blasted cold and the drain on a battery over six weeks is the pain one possibility would be to use solar panels but this is during the six month twilight anyone have any good ideas thanks in advance wes firstly i would never consider trying to make a one shot timer your f cap will have been designed as a ram battery substitute rather than for use in applications where you wish to drain the cap with a constant current their performance in some respects is more akin to batteries than to a normal cap the other point is that big electro s are usually rated with tolerances so calculating exactly what capacitance you have particularly when considering the cold you should be looking at designing a micropower oscillator and divider chain that rolls over from zero to maximum count or vice versa once every seconds if you were to use something like a hz clock you would need a divider chain of to give an error of less than one percent in the firing times over the six week period of course you could trim the hz oscillator to give you exact time but the likelyhood of the oscillator remaining exactly constant at is low anyway i would suspect that there would be far more battrey drain in firing the solenoid than there would be in the timer circuit caveat i m not experienced in low temperature electronics so i can t guarantee that this or any other approach is the best for inhospitable conditions johnh electronics department school of mpce macquarie university sydney australia email johnh mpce mq edu au ph fax
