Ever wondered how small things in our lives go unnoticed at times.
In today’s world of skyscrapers, crossing a hundred floors in a matter of few minutes is no big deal, thanks to the – Elevators! But no, we will not be talking about how an elevator works as it is primarily guided by principles that are better understood to the mechanical engineers. The whole set-up is rather complex with many control systems and processors forming the core of the elevator scheme. In this discussion, we will deal with the role of electronics in the modern-day elevator system – the display control.
(Image courtesy : www.drchaos.com )
For simplicity, we will only be dealing with the fundamental circuitry or concept underlying the displays employed. The actual connections or circuits may-be larger and heavily complicated. To give you an idea, here is a block diagram you can identify with.
What exactly are we talking about?
Here we will dig into the details behind the displays that are synchronized with the lift movement, more precisely, how does the display show “1” when we are currently at the first floor and so forth.
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Coming back to the block diagram, let us first define what a keypad matrix is. You can consider it to be the same as the buttons you see in the elevator: 0-1-2-3-4-5-6-7-8-9 and so on. When you press on a particular number, say “1”, a signal is sent to the processing unit that identifies the input as “1” and accordingly generates the corresponding output. So this is how we take the input from the user.
The next part is to process this unit in a form that is better understood by the processor. For this we employ an encoder that converts “1” into “0001” (binary) and sends it to the next block for further processing.
After the processing has been done, it is time to display the data to the user for which a device called the seven segment display or SSD is used. Now, it is the same device that displays time in a digital clock but sadly it cannot be directly connected to the core circuitry. The SSD contains a set of seven LEDs, namely a-b-c-d-e-f-g-h that light up in accordance to the input to show 0-1-2-3-4-5-6-7-8-9. Have a look:
(Image courtesy : www.electronics-tutorials.ws )
For this the connections are made via a BCD-to-seven segment decoder that decodes the input into a format that is understood by the SSD. The format of the data output coming from the counter will be in the form of binary coded decimal or BCD. IC 7447 is most commonly used for this decoding purpose. It accepts BCD and subsequently assigns a logic 1 to the LEDs that should be glowing in order to display that particular BCD, for example, if the input BCD is “0110” the decoder output will be a=1,b=0,c=1,d=1,e=1,f=1,g=1. This enables the SSD to deduce that the number 6 is to be displayed. This is how all the digits from 0 to 9 can be displayed using a single SSD.
Coming back to the processing block, it can be explained with the help of a situational example:
Suppose you enter a multi-storey building and wish to go to the 3rd floor. Your first action will be to press the button at the ground floor and wait for the lift to come down if the lift is not at the ground floor initially. Once you enter the lift, you will press the button “3” and read the display that shows: 0-1-2-3, and voila! After the lift has dropped you at the 3rd floor, it will once again go back to the ground floor i.e. now the display will be something like this: 3-2-1-0. So, how does this counting take place? It’s simple, it uses a counter. Are you asking yourself how could it be that easy? Have a look at the circuit we designed ( Click on the circuit to open it in DoCircuits ):
Carrying on with our example, the user input here is “3” (for third floor) or “0011” (binary output from the encoder). When this “0011” is fed into this counter IC as shown, the ordinary decade counter will not count up to 9 anymore, instead it will count up to 3. The initial floor is ‘0’ and it moves up to the 3rd floor. Then we have simulated a user input of ‘1’ – 0001 – at the parallel load input. This results in the display now going to ‘1’ akin to the movement of the elevator to a lower floor from the upper floor.
Therefore the lift comes back to its ground state after every cycle unless a trigger is applied to call the elevator to some other floor. Not as easily done as said, but certainly the fundamentals remain the same.
It is an irrefutable fact that some simple electronics runs at the back-end of almost everything that comprises today’s modern world, be it the metro that displays station name and other vital information, your trendy digital watches, the cool display with stock market updates on Wall Street, or of course the elevators!
See for yourself! Try the new additions to the DoCircuits panel—specialized ICs: 74190 up-down decade counter, 7485 4-bit comparator, 7447 decoder and the Seven Segment Display.