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Digital Electronics 5

Up to now we've only stored one switching condition. Even though the button was no longer pressed, the light stayed on. Now however, several switches are gathered together on an IC, hence the larger number of pins. If there were 4, one could then save four bits. Because however, with each bit that is added, the amount of possible switch-positions is doubled, thus e.g., with 2 switches there are 4 and with 4 switches there are 16 various positions.

At the latest now, the IC becomes a counter. One only needs, e.g., on a slot-car race track, one switch per lane to count the driven laps. You may now understand why, in the beginning, I mentioned the bouncing in switches. The electronics are so fast, that they would, depending on the switch position, count too many laps. The switches may trigger only once, they must, so to speak, be bounce-free.

You can learn more about seven-segment-displays here and here.

We now need a display. The LEDs are also well suited for this task because they don't need a high amount of current. Indeed, our circuit would soon be overloaded if the current-flow was too high. Now of course, it makes no sense, to use one LED per bit. The first four lit-up LEDs would then show 15 driven laps, and who wants to always have to do conversions.

You will have seen how this problem is solved in everyday use. One uses LED-bars and arranges them so that they form the figure '8'. This way, all the figures from'0' to '9' can be readably shown. Because seven bars are needed to show the figure '8', it is called a seven-segment-display. If you can now imagine several of these displays placed next to one another, basically, as many laps as you like can be shown.

Of course, it's not quite that simple. We are still dealing with bits, which don't fit into our system very well, irrespective of whether we are assign them to the binary (2-digit) or the hexadecimal (16-digit) system. To keep it simple, there are 2 ICs. One of them is a so-called BCD-counter. It has 4 switches as well, which means, it could store 16 different conditions. Because however, it is called a Binary Coded D ecimal counter, after the '9' it doesn't save any more but gives an impuls to it's identical partner, which then counts the tens. So, all that's missing now is another IC, which transforms the, not quite complete bit, of the IC blocks, made up of units, tens, and hundreds etc. directly in the seven-segment-display. There is also such a device, and in the next part, I will …
1. Reveal the secret of what one can achieve using this component,
2. show the not quite complete, but hopefully understandable circuit and try to explain it a little. 08/11

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