Seven segment displays are commonly used now days in place of dot matrix display. This can be used in many places like in microwave or fancy toaster oven or you can find the same on washing machine. On 7 segment display you can display numbers from 0 to 9 and some alphabets. It cannot display alphabet which uses diagonal lines (like R, Q etc) and you cannot distinguish between numeric zero and alphabet O.
7 segment display are labeled a to g and decimal point is usually known as DP. DP is the common point. In common cathode display pin 3 and 8 are connected to ground and rest pin are connected to supply. Similarly in common anode pin 3 and 8 are connected to supply and rests are connected to ground.
Advantage of 7 segment display-
1. It uses low power for its operation less than 2.5V.
2. Comes in industry standard size.
3. Comes with a industry standard pin out which can be directly referred from datasheet.
4. Seven segment display comes different size, user can use according to their requirement like 7.6mm, 10mm, 14.2mm etc.
5. You can also choose color of your display. Commonly used- Red, Yellow, and Green.
Following figure shows the pin configuration of 7 segment display-
Fig. 2: Pin Configration of a 7 Segment Display
Here letter “a” represents pin 7.
letter “b” represents pin 6.
letter “c” represents pin 4
letter “d” represents pin 2
letter “e” represents pin 1
letter “f” represents pin 9
letter “g” represents pin 10
Working of circuit
To operate the logic high and low indicator circuit, first momentarily press the reset switch S1 connected at pin 4 of IC1 to reset the whole circuit. When logic probe is connected to zero volts or ground, trigger pin 2 of 555 timer goes below 1.7V to make the output pin 3 high. And this pin 3 is connected with 7 segment display. At this time we will get the “L” displayed on 7 segment display 2 which means logic zero. Bi-stable multi-vibrator will hold this state until reset pin is pressed or we have change the logic level.
On the other hand when logic probe is connected to high logic, trigger pin 2 goes high more than 3.3V and output pin 3 become low and “H” is displayed on 7 segment display 1 while second display remain off.
Fig. 3: Prototype of Circuit on Breadborad showing “L” Displayed on 7 Segment
Video of the Circuit