The in-sync LED pulses each time the a 30 second pulse is received. There are 2 LEDs that monitor synchronization in-sync and re-sync. Every 0 and 30 seconds past the minute the clock checks for a 30 second pulse if the pulse arrives earlier or later it resets the clock to stay in sync with this pulse. I use 30 seconds as my slave clocks are driven by 30 second pulses. This clock goes 1 stage further and uses a 30 second synchronizing pulse (you can use any timed pulse) from my Master Clock to stay in sync. Given a bit of adjustment and a stable temperature you can get a second a week accuracy. You could use a real time clock as a time base as these use a 32.768Khz quartz crystal that when divided by two 15 times gives you a 1 second pulse. Over a few days the clock will be many seconds out. Over a short period this will not matter and will not be noticed. Microcontrollers use a quartz crystal as a time base in this case 20Mhz but as this in not exactly divisible by 2 you will never get a precise 1 second pulse. These are fixed through the mahogany base with studding. The 2 meter fixing brackets and studs can be seen protruding from the lower aluminium angle. Pic 9 shows the aluminium angle running top and bottom of the 3 meters with the meter fixing bolts clamping the meters to the aluminium angle. see pic 6 for display, indicators and control panel layout. To keep in with the industrial look I used large push and toggle switches on the control panel mounted beneath the display. This gives the impression that they are floating over the case. The meter assembly is then bolted to the mahogany base from the rear by a pair of brackets. The three meters are mounted together at the rear of the cases using aluminium angle top and bottom. Pic 5 shows the original meter on the left and meters with modified dials on the right. You can of course use any panel meter you like including horizontal or vertical mounting edgewise panel meters (pic 4). Instead I used far cheaper 7.2 x 7.2 (2.8" x 2.8") square 90° display panel meters (pic 3 left) new from Ebay Hong Kong. You may be able to pick up cheap 2nd hand meters from Ebay. I wanted to use 7.2 x 7.2 (2.8" x 2.8") square 240° display panel meters (pic 3 right) as these displays give a far greater separation between digits but these were very expensive. All these were cut to size on my table saw. I used off cuts to make the frame for the clear plastic cover (purchased from Ebay) and also for the panel meter decorative strips. I wanted an industrial/laboratory look to my clock so for the base I used a large lump of mahogany that had been laying around my workshop for years. In my latest clock I now use a sound board from Adafruit this is far more configurable and has CD quality sound. If you want to see details of this board have a look at my Voltmeter Clock page for details. The clock also has a chime board but this is completely separate from the clock and is controlled by my Master Clock so is not covered here. Synchronization to my Master Clock every 30 seconds Switched display On and Off (keeping battery backup as per Alan's design) but also allows me to turn meters Off in full power mode whilst still keeping track of time. I had a different version of Picbasic to the original code so first of all I had to convert it to run on PICBasic Pro version 3. I purchased a kit of parts from Alan's site and decided to change the design quite a bit and give the clock a retro industrial look. The instructable can be found here and website here. The clock is based on an instructable "Multimeter Clock" by abbtech see pic 2. The Microcontroller code is written in Picbasic Pro 3.Īccurate time is maintained by synchronising the clock to my Master Clock that is synchronised to a radio "atomic" clock. A PIC16F628A microcontroller is used to display the time by varying the voltage to each voltmeter and also provides very basic timekeeping. This clock tells the time - hours, mins, and seconds using 3 analogue voltmeters.
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