This is a multi-part message in MIME format. ------=_NextPart_000_009F_01C1995C.9A0D7A20 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit > I am using 32.768 KHz to get *reasonable* accuracy. The Low > Power mode is a bit of a bonus For my clocks I try to use mains frequency where possible (but directly connected, not induced) and this circuit for battery back- up during a power cut or transportation, although it will function perfectly as a driver in a battery-only system Take the movement from a cheap kitchen clock and remove the coil. What you're left with is a timebase PCB that is accurate to a few seconds per year. The manufacturer has taken care of the timing/temp issues, nice guy To the pads where the coil was joined, add these components. It is a reciprocal driver, ie the output pulse goes high (about 3V) with respect to the other pad, then the next second it goes negative wrt to the other pad. If you look at the gearbox of a kitchen clock and the reciprocating magnet on the seconds cog you'll see why. The circuit attenuates the -ve going pulse, leaving you with a 0.5Hz pulse that can be used as an external interrupt. It doesn't matter which pad you use as the "ground" or "reference", the clock output is symmetrical. Now, as well as being accurate, this also means that you can put the PIC to sleep for the vast % of the time. It is woken for a very short period every 2 seconds by a b0 INT to update counters etc. End result is good time-keeping at a miniscule quiescent current. You can't do that with the PIC's 32k crystal as the timer shuts down during sleep (F84). The F628 has a separate LP timer that runs during sleep, but for power reasons I prefer to use the very low current external timebase The rest of the clock is not wasted - you can drive it with a PIC at 5V if you include around 390 ohms in series with the coil. They are a bit finnicky about the voltage, perhaps you'll need 360R or 430R. If the second hand labours getting up towards the hour, you'll know that the R is not quite right. As I said, the gearing is reciprocal, so connect the coil between two outputs, say b1 and b2. First pulse is b1 high, b2 low. Next pulse has b1 low, b2 high. Then back to b1 high, b2 low and so on Once you have control of the timing, you can make the clock into a 24-hr one, or even a timer with a settable period. What you can't do unfortunately is make it run backwards ------=_NextPart_000_009F_01C1995C.9A0D7A20 Content-Type: image/gif; name="lowiclk.gif" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="lowiclk.gif" R0lGODlh6gCcAPcAAAAAAP////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// /////////////////////////////////////////////////////ywAAAAA6gCcAAAI/gADCBxI sKDBgwgTKlzIsKHDhxAjSpxIsaLFixgzatzIsaPHjyBDihxJsqTJkyhTqlzJsqXLlzBjypxJs6bN mzhz6tzJs6fPn0CDCh1KtKjRo0iTKl3KtKnTp1CjSp1KtarVq1izat3KtavXr2DDih1LtqzZs2jT ql3Ltq3bt3Djyp1Lt67du3jzbgTAF0AAvwQB6xUr+G/BwoO9IjYscHFirn0FSy4bubLly5gza97M uTNnjpMdfxV9lfTE0GZNV1XdcPJA1lthS5W9sO/hs6pZ0yYJmPbuvKb51mYM8zfxxwkd+13+unnj 46+FN5YeOXrv5sttGxZuuzd17c+R/issDJ646+0GUT9Xj3498+3X42N3Dr3iZbTnA9O/Hp5+//eM SWdegOvN196B+WVkXFbkCThgeJXdpl+B/RFIoXwXDnjeguOtpdx+00FHnoEIahgif9llyF6CGHFY 2nDRHVjhXwJq5xp43FnI3HcBUgciaB4a5aJ/CgZZ1JAztmhkV0imtyRkHjU5m2dUVmnllVV+JKV4 UCHWoGQ+chmVlxuaKOZTXj5YIn9nJiVamaht2aZMH/6noZxz0umknXHmyVSafM6Hp5/FTTgdmCgi VN6hANZH6EmD/ujfiI+qFKmkIuoXYaUiXYppdTSCmiSnQHZKJIlqkgqSp3Ye1CiL/qp2xGp+7FkY a0ishuqcjZqKemups7nanYSQ+YpjeYgS22WdM+bKE6U3psdmg2PWtxisWI14rZPTBmYlQ1ky+tlp 0tZ4KoMRXoujeQ7SuBK2e3VIoWKadphohc4mdy6wrqIKpb+3pTspS/BqtC2+f3rLZr+7kgjtwO/u G++u7eYLKZzjGVtjxdYpi1LBdAGonsWGWirxXRiTfDJvK+uE5cub6cunyqN+3HJONCsqs4kq58yw oz75vOfPfa4KsklH41yozh3bKuvCLiWtJcy+EnxTjnrWrGXJFAntMZ3tviR1kTfDGDXTXxtd09gW bdqk11zPKzeucKPdc9wS1S3u/rqthkq1ZmuXTbbWD+kNtL+NJhd2bYYT6/XbS8ubNtqFN27o40qK zXJEi2pOuIJXFh45rnknfvbnLo++aumoIy24TYbna5y5kVtOruemXhT764HjTnrmLbGtO+B5q741 2UJvarLuxke51+KrAR/85qDbnhLkvj+tfNedW4X96blPrNX303cKfdf/tl1czMPjab3NzGc/eeXd ox+b9FbvzH39t4//9/mQktxpLGOwuuxOf6XbnvpC1jzeUW5wcjngA+0nvgj+74ICtI+sfhW+BVaQ gxvEnwhBWMARepCE/NJgClEIQRV+EDf1elMJzTa0E7YQhgj7WfxoOD+IDOp9/lf7j418tDHvhI1X ujoUhGrowhmmJUUZcs+8RHa5NQlKh028YWqoCLXQVIdWAUOcDNv3PLZEq4uIg5jDMqWcC7pRgTgk ULdWlKqiWRGIisJj7wr0nW4lMUFIPNa9nsXC6BUygDlEFhPBdUikgWmN7vIW584EqEKNjGf18iEl U6eiTx1ugsDZEXpuRETqYUhU0dLkY7wTSS5ix2JndJx1ALhIvNCxPQIryYaomKTf6FFIkHxPJUcC xiT2cpKrPJGkauWUXwpJlH37Y7Aa+SfiUfOa1LwPNrd5Tf5x85vgDKc4x0nOcprznOhMpzrXyc52 uvOd8IynPOdJz3rakykBAQEAOw== ------=_NextPart_000_009F_01C1995C.9A0D7A20-- -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.