Clock Module- Part-2:-Monostable Timer
âMake before Break (or) Break before Make but beleive in the dreams that keep you awakeâ
Welcome back my tech aficionadosđ! Iâm very excited to be back with you all. And so my blogâšâš!!! Today we are going to build, another part of our clock module, âThe Monostable Timerâ.
So, basic question before we start, What and Why Monostable???
Answering the âWhatâ, A monostable state is a state where there is only a single state through which the function takes place at a particular time, it doesnât oscillate as of an Astable, to put in simple words, the timer will be either âONâ or âOFFâ at a time. Now answering the âWhyâ, In a circuit, we may not always require a state that is oscillating, at times we may also require a state which is under a manual control. Basically that is the idea of building a monostable timer.
To build a Monostable timer we may require,
Circuit from part 1,
1x 555 timer IC,
1x 1kΩ resistor,
1x 1MΩ resistor,
1x 330Ω resistor,
1x 2”F capacitor ,
1x 0.1”F capacitor ,
1x 0.01”F capacitor ,
1x Momentary âMicrotivity 6mm tact switchâ,
1x LED & 22 gauge wire. Come letâs get our hands dirt and dusted đ ïž
The above image is the complete representation of a Monostable state.
Here we can see a push button, another 555 timer, few resistors and a capacitor. We have used a 555 timer just because the connection could be simple and we could make some wonders out of it(wait and watch đ)!
In this circuit we have used one Mega ohm resistor(1MΩ) and a 2 Micro Farad Capacitor(2”F) which is been connected in the 6th and 7th pin of our 555 timer respectively.
You ever had such a question in your mind? Well, if yes then you are on the right track with me and if not, no issues, we will let you know đ
Every connection has a reason behind it, the 6th pin is a threshold pin, so obviously we will be using that pin for a capacitor to store and the discharge pin has been connected from the threshold pin( for pin clarification kindly check my previous blog) to discharge pin.
In the above video we can see an LED been glowing for a particular time(exactly 2 seconds). Do you know why? Itâs because we have used a 1MΩ and a 2”F. Iâll explain how.
We all know that the word 'Mega' means 10ⶠand the word 'Micro' refers to 10. So obviously when they get multiplied we will be cancelling both the powers. So only the multiplied value remains. Here we have 1 Mega Ohm and 2 Micro Farad. So once they get multiplied we will be getting 2 as the result. Which ultimately refers the duration. Therefore the 2 seconds.
If we place a 0.1 micro farad, the LED will blink only for 0.1 second or 100 milliseconds.
Wait Iâll show you
So this is the reason why we have used a Mega Ohm and a Micro Farad!
Now looking upon the circuit diagram, similar to our Astable circuit with some slight modifications. In this circuit we have given the connection of pin 2 of the 555 timer to the push button.
Well if you ask about the role of resistor in the push button (which has been connected into the 2nd pin), is to receive the power and regulate it. Now the rest of the connections in the circuit diagram is the same of an Astable timer. Even the breakdown of voltage through the voltage divider is same.
But, how come we are able to say that this is being in a Monostable state? Iâll explain how and where this monostable timer is coming into play. The 2nd pin of a 555 timer (i.e the trigger pin) initially will be having 0 volt. So which is obviously less than 1.67V( how this 1.67V came out there??? đ§ That point is the 2/3 rd of the voltage divider. For detailed explanation kindly refer my previous blog đ
Link:- https://medium.com/kgxperience/crafting-an-8-bit-symphony-building-blocks-of-a-retro-computer-b83316363a2f)
so the âSetâ part of the SR flip-flop turns âONâ. But the LED doesnât glow.
Iâll explain why. We need to understand how this push button functions before disclosing that.
A push button do have 2 metal plates inside it, initially both the plates will not be in contact with each other. But once the button is pressed, it tends the plate to be in contact with each other, which closes the circuit. And as we all know current flows only through closed circuit. Thus there will be a flow of electrons in the circuit until the button is pressed. Once released, again the plates will go back to their initial states(i.e) they will not be in contact. So obviously it leads to an open circuit. This is how the push button works.
Even here itâs the same, eventhough the condition was true. And so the reason. This is why we werenât able to see any glowing of LED at 0Volts even though (scientifically đ) it was right. Now asusual if it reaches above 1.67V it (i.e the âSetâ part) automatically goes OFF and the âResetâ part turns ON. So ultimately there will be no glowing of LED and as the capacitor gets discharged it again goes back to 0.
Hence there will be only one state at a time. Either 'ON' or 'OFFâ. So the name 'Monostableâ.
Hey techiesâ did I just miss something đ€đ€đ€đ€đ€
Oh yeah đ! there is one small guy who is been connected from the 4th pin of the timer to the power source and another guy who is connected from the 5th pin to the ground. I completely missed them as you guys missed them.. anyone got a thought??? If yes, greatđđ»đđ»kudosđ! If not no problem guys we are on the same track đđ .
Anyway jokes apart. The capacitor which has been connected to the 5th pin is another 0.1”F and the reason behind its connection is just to reduce the noise in the impulse. And the 4th pin, which is a reset pin, we have been connecting it to the Power source just to avoid tripping of the circuit as itâs directly connecting the Reset of the Comparator.
Woow! Successfully we have completed building our Monostable Timer. Kudos to all!!! đđđ. The last part of the clock module is the Bistable Timer and we will be building it in our next blog.
Stay updated! See you all soon with our next and final part of our 1st Chapter. Until then itâs a byeđđ».
Your Support! Our Adventure!!â€ïž
Connect me on:
âĄïžGitHub:->https://github.com/PranavRajeswari
âĄïž LinkedIn:-> https://www.linkedin.com/in/pranav-rajesh-9b694a241/
Reach me out through:-> pranav.mukundh@gmail.com
Circuit Connections and Diagram Credit: Abinaya Meenatchisundharam
