Elektor - Learn, Design & Share electronics

Today I uploaded the current Software. Here is a brief description of how to operate it. After powering up and showing the SW-Version the device is in clock-mode. Clock-Mode Twisting the cork up toggles between hour and minutes or seconds display. Twisting down changes brightness in four levels. Holding the cork up for two seconds changes into setup mode. Setup-Mode Here you can set the current time and time correction per day. The element, that is currently to change is blinking. Twisting down increases the value. At the maximum the value wraps around to the minimum. Holding down chages the value faster. Twisting up changes the edited element. First is minutes, second is hours and third is correction seconds per day. After leaving the last element the time is saved to the PCF with seconds set to zero. Time Correction Because the crystal is not absoluetly correct, and i didn't want to use a trimmer, the time must be corrected to keep the deviation limited. The time correction value has a range from -30 to +30 seconds per day. When the unit is powered this correction is applied each day at 1am. When it is not powered, the time is corrected when the unit is next connected to a supply. The unit keeps track of the days to correct in the date-part of the PCF8563. This can easily be used because the date is not displayed. After the correction the date is set to zero. Each elapsed day the date is increased, actually when not connected to power. So, several days without power can be corrected. How to correct time At one day, you set the time of the device exactly to the time of a known source (ntp?). The next day at the same time, you check the runaway seconds of the device compared to the source. If the device is 5 seconds ahead, set the correction to -5 seconds. To be more accurate you can wait several days an divide the deviation by the days elapsed. This is easier then to fiddle around with a trimmer cap.