Simple circuit(555 and Capacitor)

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  • Thread starter denniegst
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    Capacitor
In summary, a CMOS 555 timer can be used to create a long delay for an LED. It can be avoided using electrolytic capacitors, and a calculator is provided for this purpose.
  • #1
denniegst
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Homework Statement



circuit.jpg


Base on this circuit, how would I make the LED stay lit for 2 seconds? My knowledge goes as far as op amp and first-order circuits. I just don't know how to mathematically solve for the right capacitor that will make LED stay lit for 2 seconds because I've never dealt with a 555. Thanks

Homework Equations



KVL...

The Attempt at a Solution


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  • #2
There are calculators for doing this which you can access via Google.
They also give the formulae that they use inside the calculator.

One that came up first on Google was the following:
http://www.csgnetwork.com/ne555timer2calc.html

Do you mean to stay lit then go dark, then light up again? Or do you mean just stay lit for 2 seconds and then stay dark?

If you want long delays, like this, you could probably use a CMOS 555. These have high input impedance so you can use larger resistors and hence smaller capacitors with them.
The advantage of this is that you can avoid using electrolytic capacitors which are leaky and unreliable in timing applications. Capacitors up to 1 uF are available in non-electrolytic types.

For example, if C was 1 uF and R1 =10 k and R2 = 3 megOhms the LED would stay on for 2 seconds and go dark for 2 seconds and then repeat this.
The above calculator accepts 1e-6 Farads 1e4 ohms and 3e6 ohms for these.

There is a link in this page for a Monostable timer calculator if you only want it to flash once and then go dark.
 
  • #3
You might find the 555 timer datasheet useful: http://www.datasheetcatalog.org/datasheet/philips/NE_SA_SE555_C_2.pdf

Do you want an astable or monostable setup? (That is, flash once or blink). Under typical applications in the above datasheet, they give schematics and accompanying formulae for each scenario. These can be used to calculate the period of oscillation.
 

FAQ: Simple circuit(555 and Capacitor)

What is a 555 timer?

A 555 timer is an integrated circuit (IC) that functions as a timer, oscillator, and pulse generator. It is commonly used in electronic circuits for its simplicity, versatility, and low cost. The name "555" comes from the three 5kΩ resistors used in its internal voltage divider.

How does a 555 timer work?

A 555 timer works by charging and discharging a capacitor through resistors and comparators. When the voltage across the capacitor reaches a certain threshold, the output of the timer changes state. This can be used to control the timing of a circuit or generate a square wave signal.

What is the role of a capacitor in a 555 timer circuit?

A capacitor in a 555 timer circuit is used for timing purposes. It stores charge and releases it at a controlled rate, which determines the frequency of the output signal. The values of the capacitor and the resistors in the circuit can be adjusted to change the timing of the signal.

Can a 555 timer be used for more complex circuits?

Yes, a 555 timer can be used in combination with other components to create more complex circuits, such as a tone generator, LED flasher, or even a basic microcontroller. Its versatility makes it a popular choice among hobbyists and professionals alike.

What are the advantages of using a 555 timer in a circuit?

The advantages of using a 555 timer in a circuit include its low cost, simplicity, and versatility. It can be used in a wide range of applications and can be easily customized by adjusting the values of the components. It is also widely available and can be found in most electronics stores.

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