Math of the Astable 555 Timer
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- เผยแพร่เมื่อ 28 ม.ค. 2016
- How are the timing formulas derived and how do you work with them? We'll also look at an example using real values to find the components needed for a particular output frequency.
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Jason, I've read just about every book from our public library on trying to understand the basic building block of IC's: the 555. I have also watched most of the 555 videos here on youtube, so I feel that I am fully qualified to say that you have the easiest to understand and most comprehensive, in-depth, excellently articulated explanation on the 555. Well done! Thank you for spending so much of your valuable time on creating Part I and Part II and also the Math Behind the 555. Bravo!!
No words to say how awesome you explained…., great work. Keep it up bro
Thanks for the encouraging words!
Thank you! Except for the fact that you never said what 'e' was this was the best video tutorial I have seen. Clear, simple, sped up past the laborious parts, no crappy music etc. I appreciate the time you spent making/editing it too!
In engineering, they teach that if you wait five time constants (5RC) the capacitor is charged "all the way" or "it's safe now", etc. Something like you are saying at about timestamp 7:00
I work with high-energy electronics, and had to learn for myself that this cam be an assumption that will KILL YOU!! I realize that this will not be usually encountered in 555 circuits, but be sure you are aware of this on large scales, such as the big "pulse" and "energy" caps. If you wait 5RC, then the cap is discharged down to 1-exp(-t/RC) or 1-e^(-5), which is over 99% discharged. Now consider the huge capacitors that so many people are using for such things as "wire exploding", "rail guns", "can-crushing", etc. I have seen some cap banks that are charged to energy levels like 75kJ. If such a bank is discharged 99.3% (5RC) it is left with an instantly lethal 525 Joules!!
I believe that these things are the most dangerous electrical components!
BTW: at about timestamp 4:00 I think there is a mistake in the datasheet in the last formula visible...isn't the duty cycle given by "D=(Ra+Rb)/(Ra+2Rb)"
THANKS MUCH FOR THE VIDEO!
I love your videos. The detailed information you provide and the format in which you provide is exceptional!
Thanks!
More maths stuff Please, buck, boost, op amps, inductors, circuits, mosfets ......... . I hope i can apply this to other areas and make it work. keep up the good work, very clear.
Nerd!
You've produced a great series of videos explaining the 555 Timer, thanks. I realize it's been two years since you posted, but the videos are "timeless". You really have explained slowly, and with some great grocery bag illustrations (from Whole Paycheck), what the 555 does, how it works, and how to determine what (and size of) components needed. The one thing that slipped me up on the final calculation of R sub b resistor was the 820 picofarad capacitor. In my HP 12C (the best calculator every made!), I converted 820 pico farad to micro farads (1/1,000,000). I believe you may have done so in your TI equation, but was just difficult to see that. Or, maybe you converted to milli farads AND converted the frequency to Hz, I couldn't tell.
Skinny R&D
Thank you for this video.
I have a much better understanding of how a 555 timer works now.
Also learned the formulas for calculating the time to charge a capacitor.
Great! Glad it was helpful.
Awesome video
Keep working good
We are with you
Thank you 😊
for explaining every content. ..
Thank you very much for these educating videos!!
Skinny R&D! Thank you for sharing your experience. I have a unrelated question for the topic, and that is what is the best device to emit ultrasonic frequency in air? As I noticed Speakers are too slow to vibrate for the ultrasonic frequency range.
Hi... Just came across your TH-cam videos... I really like your brown paper bag "Board" for displaying your information. I've viewed a couple of your older vid's and find them very informative as I am a bit Neophyte to electronics. I hope I will not become to much of a pest as I know I will be asking questions down the road :-D Thanks again for your informative and instruction videos... Keep up the great work.Sal.
Thank you so much!!! This helped a bunch.
Great videos on the 555! I'm a beginner when it comes to electronics, so these really helped me understand the logic behind how these work.
There is a project that I've been messing around with where I have a signal pulse coming from an electric motor which pulses twice per rotation, so the frequency is variable and equal to two times the RPM of the motor. What I would like to do is use this signal to generate another pulse which is equal to three times the RPM of the motor.
Do you think that there might be a simple way of accomplishing this (electronically), aside from using something like a microchip to be able to interpret the original pulse signal and calculate what the signal would be if multiplied by 1.5?
Ideally, I would like to have every second pulse of the original signal synced to every third pulse of the generated signal.
Edit: I may just end up creating a custom rotor with 3 magnets and a hall-effect sensor to get the specific pulse signal that I want instead of using the signal coming off the existing wire. I'd prefer not to add additional mass to the rotating component of the motor, but it's the easiest thing that I can think of for testing purposes.
Really good explain!! Thank You
Hi Jason. How can I control the duty cycle of the 555 timer in astable mode from max value, down to about 40 or 50% using LDR without significant change of the frequency? My goal is to control the brightness of big LED clock depending on the ambient light. So in the daylight it should be on full brightness and during night the brightness should be down to 40 or 50 %. My LDR values: light resistance about 1.4K, dark resistance is about 20K. By the way, subscribed and hit the bell as well.
Thank you so much for the video!
Where did you get that 1/5 for capacitor charging?
I love your videos. I also initially used a 555 for a 40kHz Ultrasonic Transmitter. Although the 555 did the job admirably (after coming up with many non-standard resistor values until I got "close enough"). I eventually replaced the circuit with a 3.2mHz oscillator can through a toggling flip flop to get 1.6mHz and then divided that down to 40kHz. It didn't really perform much better than the 555 version, except for stability. :) I am subscribing.
Thanks for the tip and the sub!
awesome videos man.. keep em coming
Thanks! I'll try.
Thank you. I'm surprised I understand the part of the video explaining the constants 0.693 and .05 is because of the 3V and 6 V concept.
I'm really weak with algebraic manipulation. I have to use examples (like you showed) and then write simple spreadsheets to do my math.
you should add a link at 11:14 to a separate video working out the equation long hand.
what Happens if you change the 10nF cappacitor (between pin 5 and ground) to a different value? is there a formula?
Would you please explain in brief about pin 5 of the ne555 timer ic.
Thank you so much!
The circuit and its math becomes easier if you control the astable multivibrator by a single resistor between the output pin 3 and the timing capacitor pin 6, leaving the discharge pin 7 unsused. In this way you also achieve 50% duty cycle.
hi, how to calculate 555 timer blinking rate that just using one resistor Rb only?
I've been watching and enjoying your 555 timer videos. Hope you're still checking the comments. I didn't see you address, or any comments about, making the output low time 3 times longer than the output high. Is this possible with a 555 timer or cascading 555 timers? For instance, say I want an LED to blink for .5s then turn off for 1.5s. The cascade example used Vhigh=Vlow. I tried running the numbers with Vhigh=3Vlow, but I ended up with negative values when I combined the equations from the datasheet.
Add a resistor coming out of pin 7 and connecting between Ra and Rb. This should slow the discharge time enough to achieve what you want.
Interesting. I'll give that a shot. Thanks!
You got an excellent channel. Though I'm very bad with the math... How would I work out a 2hz freq for a bike flicker light? I roughly guessed out the math for 2hz using (1kohm+2x1kohm) x 0.000220 farad or 220uf cap but it was all guessing took hours lol.
+clarkdef Thanks for watching! I would use: Ra = 1kΩ; Rb = 360kΩ; C = 1.0µF This should get you very close to 2Hz. You had your math correct, but you really want Ra to be much less than Rb. This will help ensure the light blinks on and off for an equal amount of time.
Great video, but what about the duty cycle? How do i make a 50% duty cycle oscilator
Using this circuit it is impossible to achieve 50% duty cycle. But you can achieve it easily if you control the capacitor over a resistor which is connected between the 555 timer output pin 3 and the timing capacitor pin 6. Operating the astable vibrator in this way saves also one resistor (you need just one resistor and one capacitor). And also in the formula you don't have Ra anymore.
yeah! great video as usual..... please cover all types of multi vibrator. please make that happen soon .
thanks for helping !
+ELECTRO BANGLA Thanks! If you have a particular project in mind, feel free to leave your ideas.
+Skinny R&D make a single video on just practical circuit of Astable, Monostable & Bistable multi vibrators with 555 timer . i think u do not have to explain a lot for Monostable & Bistable coz i think after that u've already been explained Astable ,the other two types will be easier to understand .
i am thinking of making a power supply(DC ) with a 555 timer which will multiply the voltage level and also provide negative voltage which will be converted from positive voltage source (DC).
Oh another question, what is the value of the cap to ground from pin 5?
+clarkdef its usually 0.01uf .its a bypass capacitor helps to prevent any noise problem .
Hey ur videos are good ....does 555 timer have maximum frequency to produce....and can you help on designing a range of frequency?
Mage Jose what fq?
Thank you
ultra sonic what? xD what's that thing you builded?? and can you explain more the frequency? lets say i want an led to ligth up for a secand and then be of for a secand does that makes my F=0.5hz?? (F=1/(1+1))
+Make Electronics You are correct. The frequency you would be 0.5Hz.
+Skinny R&D thanks :D i sended you a msg on your facebook page i hope you replay xD its by the name haytham ltifi
Nice explanation and nice video. However, I think it's a bit of a belabored explanation. The 0.693 comes from the fact that the voltages swings from 3V to 6V for Vs = 9V, i.e. exactly a factor of 0.5 between 3V and 6V. This factor of 0.5 is constant regardless of Vs because the voltage swing is from 1/3 to 2/3 (i.e. exactly a factor of 0.5 = (1/3) / (2/3) ).
Sir! Im Confused on the calculation. (1-e .693RC/RC) = (.0499926) How???
The formula is (1-e^(-0.693RC/RC)). Both R and C cancel out and the resulting formual equals approximately 0.5.
So what is e?
Ah sooooo, I'm guessing its Euler's number, correct? Thank God, for Google search.
Google, the fountain of all knowledge.
0.693 is really just ln(2). Remember that the ln and e wipe each other out. Since e^-0.693 = 1/e^0.693 = 1/e^ln(2) = 1/2 = 0.5, Our formula becomes Vs * (1-0.5) = 6 * 0.5 = the 3 volts
Thank you so much we wanaa more tutorial
i wanaa explain shift register can you please
great video! (:
Thanks!
Ps .......... great work .......... of course , the other question is , how accurate is the 9V , as i ' m sure that has a coach & horse of " exactly " , running through it ' s garden . And in reality , is this not the problem ? We a sold a digital pup on the horns of an analogue dilemma .......... Ok , this may be a better solution of an analogue only dilemma .......... but it ' s still a dilemma .
0 . 39 "..........hit 40 KHz exactly ............. " how exactly ? +/- 0.5 % ? +/- 5 % ? ............. how exactly is exactly . A gold band or a silver ?
It's probably impossible to answer. Two wires could have inductance and/or capacitance (more likely both). That is, the PCB itself, wires on the resistors etc. When we mix inductance in the circuit, the math gets pretty ugly.
This is the thing i like about engineering ........ there is the theory & maths & then the reality ......... it ' s amazing anything works at all !
It ' s the sort of reasons the Russian built rocket engines in the 60's that the Americans are using now .......... but then,this is the nation that also built nuclear "jet" & kept the crews safe,but rotating them of the craft before they glowed too much !
What happens if you short R(a)?
+Matthew Ferrie If you short R(a), there will come a time during the cycle when the voltage source will be directly shorted to ground through the 555 timer. This state is highly undesirable.
+Skinny R&D So it'd likely burn out?
+Matthew Ferrie Yeah or your battery will not last very long.
why did you use formula instead of numbers its very confusing but whatever
d: great question. this can be seriously confusion. here's the disambiguation:
Formulas are algebra-style generic representations of how and where to plug in the actual numbers for your specific situation. The letters are "variables" until they get fixed up with their specific numbers. Then they are "fixed variables". Numbers already appearing in these equations are called "constants.'
It's a serious issue in education that teachers and professors usually don't bother to explain this. The purpose of algebra, by the way, is to figure out what "x" is.
... that's not to say that this 555 math is really that understandable. What I have a chance of understanding is the "plug-and-chug" part, that is, put the numbers in and get the answer. The underlying physics and engineering is something else (requiring years, or in my case more like decades, of study).