Astable Multivibrator Mode of the 555 Timer - brought to you by Solderstick Wire Connectors
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- เผยแพร่เมื่อ 3 มิ.ย. 2024
- Astable Multivibrator Mode of the 555 Timer
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In this video we look at the 555 timer in its astable multivibrator mode, this mode also known as free running oscillator mode is the most common use of the IC. By controlling the time to charge and discharge the capacitor we can control the frequency, by adjusting the values of the charge/discharge resistors we can shape the mark/space ratio, and by tying pin 2 (trigger) to pin 6(threshold) we can cause the 555 to retrigger itself.
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The ratio difference between resistor value and duty cycle is interesting (1/3 -2/3 for equal resistors) - rough rule of thumb seems about 10 to 1( R1 - R2) to get nearer 50% duty cycle
Great video once again. How about a video on how to use crystals? I can't recall seeing one anywhere
Thanks for the vid, nice explanation of operation.
There are some nice online calculators that let you put in the value of the capacitor and resistors and they tell you the frequency and duty cycle of the output.
The curious streak inside of me has me interested in knowing the exact value of those resistors and the exact capacitance.
Anyway. Nice videos.Much appreciated. Keep it up!
Off hand, I don't remember but I always use multiples of 10 for resistors. In this case they were the same value. As for the cap...again I dont remember but you can use a 555 Astable calc to get your values. Here is one from Digikey: www.digikey.com/en/resources/conversion-calculators/conversion-calculator-555-timer
Thank you so much for these. I hope you’re doing well post-op.
I am!
I'm unsure if you've done this. However it'd be really neat for you to make a video on the 556. Timer 1 being in monostable, and timer 2 being in astable. Having the output of timer 1 activate timer 2 via a transistor.
I'm doing that now to have a piezo beeper go off every second after a set amount of time. Anywhere from 0-6 hours using a 20k pot and 1000uf cap. For the astable side, I'll use a 2k resistor and another 1000uf cap.
EDIT: Maybe I can't do this with the 556. Since both timers share the same VCC. So I'm unsure how I would activate timer 2 in astable mode once timer 1's output goes low
Hi there. What is the purpose of the 10 nanofarad capacitor if we choose to use it? What would happen if it was not used? Also, what is your source voltage on VCC, 5vdc? thx.
The capacitor reduces the chance of noise on the control voltage pin which is connected to one of the internal comparators used in the timing circuit (independently of the external resistors and capacitor). Any noise can shift the timing. There's an earlier video which explains (all about the pins on the 555 timer). I'll hazard a guess that Vcc is 6V (the scope shows 5.36V pp signal).
@@ralphj4012 Thank-you for this explanation..
Could someone explain the point in using these? A sinusoidal voltage over a diode accomplishes this same thing and comparators make cleaner square waves.
I'm sure there's some point, after all, it is the most widely used integrated circuit in the history of electronics.
Is it possible to change the rate without it changing the frequency?
The rate is the frequency
@@peddlereffects No. The *Frequency* is _how many cycles in a second_ while the *rate* is _How long is one state compared to the other._
@@poykehmusic isn't that the duty cycle?
Well the *duty cycle* is the rate _(or ratio)_ of the pulse width to the total cycle _(or period)_ of the oscillation. So the correct name _should be_ *duty cycle,* but SelectaBwoy use the word "rate" so I thought he _meant_ duty cycle. In fact, *frequency* is kinda also a rate, since it's the number of oscillation per seconds. It gets confusing... 😀