![]() I had to use a long USB cable for programming during development because the electrical noise from my PC was interfering. The multiplexed display has to be turned off while it is in use, so it is not possible to see the current time when it is being re-synchronised. I bought it for a few pounds and it works very well, although like most low frequency time code receivers it is extremely sensitive to noise. Since the time is re-synchronised with the MSF signal every night that is more than adequate.Īn MSF receiver module is connected to the AVR. In my initial tests on the bench it varied by less than one second per day, but when installed in the clock case it looses about 3-4 seconds over 24 hours. The AVR uses a 12MHz crystal which is accurate enough for keeping time. I removed the controller IC and all other unused parts. I connected the anode transistors to the AVR with 2k2 resistors to limit current and the cathodes to a 74HC595 shift register via a ULN2803 Darlington array. Only the middle two 7 segment displays have dots. The display is multiplexed with simple transistor switches for the common anode. I started by tracing the connections between them and mapping out how the display worked. The original clock electronics used two PCBs, one for the 7 segment LEDs and another for the clock controller and support hardware. Hour chime with choice of melodies and no chime between 00:00 and 08:00.Alarm with choice of 5 polyphonic melodies.To make the project more interesting I decided to use the ATtiny2313 microcontroller with only 2k flash ROM and 128 bytes of RAM. ![]() I decided to convert a digital clock I bought into one set by the MSF signal. Many commercial clocks use it to automatically set themselves. The National Physics Laboratory broadcasts a time signal, previously known as the Rugby clock but now called “Time from NPL.” Its most commonly known as the MSF signal due to it originally being identified in Morse code those letters. ![]()
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