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14th  November 2010
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A very useful freeware programme (not to be used commercially) that will calculate the values needed to give a particular delay – is available for download here.
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Using the 555 Timer, 741 OP Amp and … others
The 555 IC can also be used to generate a series of pulses. If an output state is ‘On’ it can be represented by a ‘1’ and if it is ‘Off’ it can be represented by a ‘0’. This gives the ‘square wave’  pattern seen here where the top sections of the line (the on-periods) are called the ‘MARK’ and the lower sections )the Off-periods) are called the ‘SPACE’ .  The number of ‘on-off’s’ in a second is called the ‘FREQUENCY’ of the output.  There is a lot on www about the 555   The units of frequency
are HERTZ (Hz) - (see Heinrich Hertz)(and Frequency)
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* Pin numbers are always shown – but may for convenience be shown in different positions.
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The major point to remember are the different units in use.    Frequently the Capacitance will be measured in Microfarads (F x 10-6) or nanofarads (Fx10-9 ) and the Resistance in either K ohms (103) or M ohms ( 106).  These calculations are just really a matter of moving the decimal point around.  A calculator isn’t needed although that will obviously make things very easy.
As was mentioned for the ‘Monostable’ calculations - If you are familiar with scientific notation then adding the powers easily gives the answer.  If you prefer to move the 0’s  - simply cross off each of the 0’s  to the right of the decimal point as one from the left of the decimal point is crossed off. ( Remember the last two 0’s shown here on the Capacitor’s value would not be included as 0.000100 is really 0.0001.   Once the decimal point is reached then the 1 will move to the other side of the decimal point and then 0’s will be tagged on.
Graphic illustration of the on and off sequence produced by the ‘astable’
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IWB Electronics Wordsearch
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