Seven Segment Display (SSD)

Displays always add an extra attraction to any project. And when it comes to representing numerals, seven-segment displays are the most preferred over other types of displays. Basically, it’s nothing but a combination of 7 LEDs which gives the 10 numerals (0-9) & some alphabets (A/a, B/b, C/c, D/d, E/e, F/f). Okayy, this may be more than enough for the introduction. Let’s try to dive into this tiny thing for some more details.

Why All These?

It’s true that working with these devices practically is a more convenient way to learn than reading articles on them. But knowing what’s going inside them may give a better understanding that can help in modifying them for developed projects.

What’s Inside?
It’s evident from the name that the 7 ‘Segments’ indicate 7 LEDs with an additional LED. This additional LED serves the purpose of the decimal point (DP). As LED’s are basically diodes, a two-terminal device, they can be powered up with respect to either of the terminals. Depending on this, we find two variants of SSD;

· Common Anode Display (CAD) or Common Vcc [All the anodes are shorted inside]

· Common Cathode Display (CCD) or Common ground [All the cathodes are shorted inside]

Physically 10 pins are visible from outside among them 8 are data pins and two are marked as ‘COM’. Com pins are basically the shorted anodes or cathodes and either of them needs to be connected with the source (Vcc/GND). The pins & LEDs are categorized using alphabets.

Working Principles
Being a digital component, SSD needs digital pulses for functioning. So it’s very simple. We just need to send pulses to the LEDs that we want to turn on. For example, if we want to show 7 on the SSD, the values we need to assign are,

a	1
b	1
c	1
d	0
e	0
f	0
g	0
DP	0

SSD can be interfaced with numerous development boards like Arduino, Raspberry Pi or PID Micro-controller. Again there is a dedicated decoder IC to drive SSD known as BCD to seven segment decoder or IC-7447.

Arduino Interface
We need to connect the 8 data pins of SSD to 8 digital pins and the COM pin to the source or GND. For showing a specific number, we just need to high the state of the required pins of the Arduino. But if we want to make a sequence of numbers, the code has to be modified according to the requirement of the project.

7447 Decoder IC Interface
Here we just need external circuitry to convert the decimal numbers into BCD (10 to 4 line encoder). 7447 Decoder IC will convert them digital pulses and the number is visible in the SSD.

Now, there exist a number of modules that provide reduced data pins, multiple SSDs on one board with many more advanced modifications. But the basic working function is the same and it has made the SSD one of the simplest and most preferred digital displays that are widely used in calculators, digital watches, microwave oven, electric meters, etc.

Throughout the blog, have you noticed the unique feature of this display? SSD can represent 0-9 & A, B, C, D, E, F; a complete unit of the hexadecimal number system. Interesting, isn’t it?





Image source:
* circuitdigest.com
* parallax.com