IAN LANG ELECTRONICS

The first question concerns itself with the 555 timer:

A Level Electronics

A Level Home

AQA Unit 2-Further Electronics

There is a possibility of gaining nine easy marks here provided you've done your homework on the 555. The first question:

 

1 (a) What type of signal is required to trigger the monostable?

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(2 marks)

And your answer needs to look something like this:

The monostable triggers when the trigger signal declines and takes the trigger to less than a third of supply voltage Vs.

1 (b) Explain how the monostable circuit functions once it has been triggered.

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(5 marks)

Once triggered, the output goes high and the discharge switches off. The capacitor now charges up through the series resistor, in this case 10k. Once the voltage across the capacitor reaches 2/3rd that of Vs, the discharge goes back on and the output goes low.

1 (c) Calculate the time period of the monostable.

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(2 marks)

To get your full two marks here they want you to show you understand the time constant for the monostable. So you write:

 

T = 1.1 R C

 

 1.1 x 10 x 10 = 0.11ms

4

 

-8

 

Observe the scientific notation there. They'll be expecting to see that.

 

And that's it. 9 very quick and easy marks.

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