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 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;
It’s evident from the name that the 7 ‘Segments’ indicate 7 LEDs with an additional LED. This additional LED serves the purpose of 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]
Image
source: circuitdigest.com
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.
Image
Source: Parallax.com
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,
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 Microcontroller. 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.
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.
Arduino
Interface
Image Credit: Engineer’s Articles
Image Credit: Engineer’s Articles
7447
Decoder IC Interface
Here we just need an 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.
Here we just need an 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.
Image
Credit: Engineer’s Articles
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 same and it has made the SSD one of the
simplest and most preferred digital displays that is widely used in
calculators, digital watch, 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 hexadecimal number system. Interesting, isn’t it?
