-38-
Now you will learn about a common-cathode,
seven-segment, LED digital display. Common-
cathode means that the seven LED display
segments use one contact point – terminal 25 – as
a common negative electrode.
The LED must have (+) and (–) connections so that
current can flow through it. The positive side is
called the anode, and the negative side is called the
cathode. Because the seven-segment display
consists of seven LEDs (not counting the decimal
point), there should be 14 connection points in total
– seven anodes and seven cathodes.
However, we can make either anodes or cathodes
common, making the number of terminals only eight
– one whole anode terminal for each of the even
segments and one terminals to act as a common
cathode (or seven cathode terminals and one
common anode).
The LED display in this kit is a common cathode
type. You connect the common cathode segment
terminal (terminal 25) to the negative side of the
battery, and any anode segment terminals as
required, to the positive side of the battery.
LEDs operate extremely fast. An LED can turn on
and off hundreds of times each second; so fast you
can’t see it blink. Unlike an incandescent lamp, there
is no warm up time, and no great amount of heat is
produced.
Perform the following experiment to see how fast the
LED operates.
1. Hook up the circuit but do not close the key.
2. Decrease the surrounding the room light to a
very low level so you can see any LED light
emission easily.
3. Close the key for only a fraction of a second.
Notice that the display goes quickly on and off. Now
hold the platform steady but glance quickly across
the LED display as you briefly tap the key. The
display should appear to go abruptly on and off.
Actually, the persistence of the human eye is much
longer than the LED’s on time, but without special
instruments this gets the point across.
Notes:
EXPERIMENT #24: BASIC LED DISPLAY
Wiring Sequence:
o
17-18-19-20-21-22-23-24-138
o
25-120
o
119-137
Schematic
Содержание EP-130
Страница 11: ... 11 I ENTERTAINMENT CIRCUITS ...
Страница 26: ... 26 II BASIC SEMICONDUCTOR AND COMPONENTS CIRCUITS ...
Страница 36: ... 36 III LED DIGITAL DISPLAY CIRCUITS ...
Страница 41: ... 41 IV A TOUR THROUGH DIGITAL CIRCUITS ...
Страница 49: ... 49 V MORE ADVENTURES WITH DIGITAL CIRCUITS ...
Страница 64: ... 64 VI THE WORLD OF TRANSISTOR TRANSISTOR LOGIC ...
Страница 77: ... 77 VII APPLICATION CIRCUITS BASED ON THE OSCILLATOR ...
Страница 88: ... 88 VIII BASIC OPERATIONAL AMPLIFIER CIRCUITS ...
Страница 116: ... 116 IX MORE ADVENTURES WITH OPERATIONAL AMPLIFIERS ...
Страница 129: ... 129 X COMMUNICATION CIRCUITS ...
Страница 136: ... 136 XI TESTING AND MEASURING CIRCUITS ...