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555 Timer. What are they and what do they do?. What do they do?. Many electronic systems require a timer to control their operation. The popular 555 timer IC can be used to produce two types of timed output. Monostable Astable. What’s inside?. That’s. 16 Resistors. 22 Transistors.
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555 Timer What are they and what do they do?
What do they do? • Many electronic systems require a timer to control their operation. The popular 555 timer IC can be used to produce two types of timed output. • Monostable • Astable
What’s inside? That’s 16 Resistors 22 Transistors 2 Diodes
Pin Configuration and Set-Up • The 555 is mounted in an 8-pin DIL package • Connecting pins 1 and 5 to earth or ground, followed by pins 4 and 8 to the supply, powers up the timer. Output pin 3 powers devices like LED’s, buzzers, small motors or in fact other circuits turning them on or off.
Trigger, Threshold and Discharge Trigger - This pin is the input which in turn causes the output to go high. Threshold - Is one input which causes the output to go low. Discharge - This pin is connected to the open collector of a NPN transistor (Q14), the emitter of which goes to ground.
Monostable • A monostable has only one stable output state. • It is in this stable state with the output at OV. • The length of time for which the output is in this ‘temporary’ state is determined by two external components, a resistor and a capacitor.
Astable • An Astable has no stable output state. • The output will constantly switch between HI and LO. • The length of time for which the output is in either of these states is determined by the resistor and capacitor arrangement.