Some of the circuits in this chapter are large, and you might need to zoom out your browser screen to see the entire circuit on the screen.
This is a binary clock. It displays seconds (at the top), minutes, and then hours in binary-coded decimal (BCD), with an AM/PM indicator at the bottom left Each group of three or four flip-flops is one decimal digit. For example, 010 0101 is 25.
This clock does not display the correct time.
This binary clock is the same as the first one except that it includes two buttons at the left that let you set the clock to a particular time. Press the top square button at the left to set minutes, and the bottom square button to set hours.
Timing is based on the Javascript animation facility, so it may not keep exact time.
This circuit shows how a closed-cathode display (commonly called a Nixie tube) can display digits 0 through 9.
A seven-segment display is a little more complex because decoding circuity is required to illuminate the various segments.
A dot-matrix display is even more complex because only one column of dots (or in other configurations, only one row of dots) can be illuminated at any time. This requires circuitry that quickly cycles through all five columns to trick the eye into believing that it's all lit up at once. (The effect is exaggerated here.)
Also required is a type of read-only memory that contains the dot patterns of the digits. In this circuit that's provided by arrays of diodes.