555 IC — Monostable Mode
Playing with 555 Timer — Part I — Monostable #basicTronics — 05
Monostable multivibrator (one-shot): it just gives one pulse and you have to trigger it again to get another. It generates a single pulse when triggered.
Summary
When Voltage on the triguer (Pin 2) drops bellow 1/3 the full supply voltage, pin 3 output high.
Components You will need for these breadboards:
1 x NE 555N IC
1 x 8-pin socket
1 x capacitor 470 uF
1 x capacitor 0.1uF (104)
1 x resistor 10k
1 x resitor 1k
1 x resistor 470R
1 x potentiometer 22k
1 x Arduino Uno
1 x breadboard
1 x button
1 x LED
How It Works!
When watching the video above, look carefully at these components:
Inside the Chip
2 x internal comparator A& B: each compares 2 input and delivers an output dependant on whether the inputs are similar or different;
Pin 2, trigger, a negative pulse on this pin sets the internal Flip-flop to down position when the voltage drops below 1/3Vcc;
Pin 6, threshold: this pin is used to reset the Flip-flop to up position when the voltage applied to it exceeds 2/3;
FF: it is a big Flip-flop DPDT switch (works as if it were). Both load terminals can be energized at the same time. They are independent of each other but works together.
Outside the Chip
Capacitor C4 and Resistor R4.
The width of the pulse, T, is determined by the values of R4 and C4, as follows:
Formula for Monostable Mode
T = 1.1 x R1 x C1 Usage
Safely Trigger — You can use a one-shot to safely trigger a digital logic device.
Debouncing Circuits — Mechanical switches tend to bounce when closed, producing multiple voltage spikes that a digital IC can misinterpret as multiple trigger signals. Instead, if you trigger a oneshot with a mechanical switch and use the output of the one-shot to trigger the digital IC, you can effectively debounce the switch.
(…)
Help me list more 555 applications in monostable mode by commenting here!
HowItWorks Video Script (from Book Make Eletronics, Experiment 16: Emitting a Pulse, by Charles Platt — Thank you, man!):
If the voltage on pin 2 drops to 1/3 of the supply, comparator A notices this, and flips the flip-flop. This sends a positive pulse out of pin 3, and also disconnects the negative power through pin 7. So now C4 can start charging through R4.
While this is happening, the positive output from the timer continues.
As the voltage increases on the capacitor, comparator B monitors it through pin 6, known as the threshold. When the capacitor accumulates 2/3 of the supply voltage, comparator B sends a pulse to the flip-flop, flipping it back into its original state. This discharges the capacitor through pin 7, appropriately known as the discharge pin. Also, the flip-flop ends the positive output through pin 3 and replaces it with a negative voltage. This way, the 555 returns to its original state.So this is it!
In the next post, We will playing with 555 in its bistable mode!
So till then, catch up with me by posting your comments in my youtube channel!
And don’t forget to thumbs it up;-)Enjoy!
Download All Files for This Project
References & Credits
555 TIMER BASICS — MONOSTABLE MODE
Book: Make: Electronics (Learning by Discovery) 1st Edition
Proteus — IC 4026 — Reaction Timer Circuit
Proteus — IC 555 Timer — Debounce Circuit
tips and tricks:
Use 8-pin socket for 555 IC.
It works better!
I wasted a lot of time on fake contacts on the breadboard, so save your time!
Slides: How_555_Mono_Works
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