The value of the first column can now be set to any desired value using S2. If you press S2, you will arrive at the setting menu after a brief LED test (all LEDs on). Buttons S1 and S2 can be used to set the time. In order to nevertheless make the low-current LEDs nice and bright, the magnitude of the current pulses is made significantly higher than the rated current. As PIC16C54 does not have enough output ports to individually drive all of the LEDs, and doing so would also require several additional components, the display is multiplexed. The voltage must not be rectified, since the microcontroller uses the frequency of the ac voltage (50 Hz) as a clock signal with long-term stability. The supply voltage for the circuit comes from a simple mains adapter with an ac output voltage of 8–15 V at a maximum output current of 300 mA. With a bit of practice, it’s even possible to quickly and easily read the time in a single glance. The values are read row by row from top to bottom: one, two, four, and eight - in other words, binary. However, the hours, minutes and seconds have been further divided into units and tens to make them easier to read, which yields six columns: tens of hours, units of hours, tens of minutes, units of minutes, tens of seconds, and units of seconds. The version presented here is based on the binary clock (not yet on display) in the new Museum of Mathematics in Gießen, Germany (de/htdocs/mathematikum/index.php?5 13), but it is entirely compatible with an ordinary living room. Unusual clocks are not uncommon in Elektor Electronics.
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