10th April 2007
IF IN DOUBT ASK !!!!
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.
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) -
are HERTZ (Hz) -
* Pin numbers are always shown – but may for convenience be shown in different positions.
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.
The answer units will be ‘seconds’
The answer units will be ‘seconds’
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’
