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					                        THE 555 TIMER

1. The monostable – this will allow the circuit to standby, power on,
until a trigger is activated to PIN 2. When this happens the IC (555)
will switch on the output for an amount of time determined by the
resistor / capacitor network which is connected to PINS 6 and 7. The
output is always connected to PIN 3. The formula required to determine
the time delay is:-

t (seconds) = 1.1 x R (Mega Ohms) x C (micro Farads)




Example:

t = 1.1 x R x C = 1.1 x 0.01 M x 220uF = 2.42s

This means the relay will be energised for 2.42 seconds and therefore the
bulb will be lit for this length of time.

Questions : using the formula shown calculate the time delay for the
following values


1.    R = 1M       C = 10uF

2.    R = 2M       C = 100uF

3.    R = 100k     C = 47uF

4.    R = 330k     C = 22uF

5.    R = 68k      C = 1uF
1. The astable – this will continuously switch the voltage at the output
from 0V the Supply Voltage in a regular square wave pattern. The
output is always connected to PIN 3. The formula required to determine
the frequency of the switching action is:-

frequency (Hz) =        1.44
                   _________________________

      (R1 (Mega Ohms) + (2 x R2 (Mega Ohms))x C (micro Farads)




Questions: USING THE FORMULA CALCULATE THE FRQUENCY
IN Hz FOR EACH OF THE SET OF VALUES BELOW.

1.)   R1 = 1kΩ     R2 = 47kΩ C = 10μF

2.)   R1 = 1kΩ     R2 = 22kΩ C = 10μF

3.)   R1 = 10kΩ R2 = 220kΩ C = 100μF

4.)   R1 = 10kΩ R2 = 1MΩ C = 100μF

5.)   R1 = 100kΩ R2 = 1kΩ C = 1μF

				
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