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INTRODUCTION
This e-book covers the 555.
The 555 is everywhere and it is one of the cheapest and most-rugged
chips on the market.
It comes as a TTL 555 and will operate from 4v to about 16-18v. It
costs from 20 cents (eBay) to $1.20 depending on the quantity and
distributor. The circuitry inside the chip takes about 10mA - even
when the output is not driving a load. This means it is not suitable for
battery operation if the chip is to be powered ALL THE TIME.
The 555 is also available as a CMOS chip (ICM7555 or ICL7555 or TLC555)
and will operate from 2v to 18v and takes 60uA when the circuitry
inside the chip is powered. The "7555" costs from 60 cents (eBay) to
$2.00
We call the TTL version "555" and the CMOS version "7555." This is
called ELECTRONICS JARGON.
The 555 comes as a single timer in an 8-pin package or a dual timer
(556) in a 14 pin package.
The 7555 comes as a single timer in an 8-pin package or a dual timer
(7556) in a 14 pin package.
The 555 and 7555 are called TIMERS or Timer Chips. They contain about
28 transistors and the only extra components you need are called
TIMING COMPONENTS. This is an external resistor and capacitor. When a
capacitor is connected to a voltage, it takes a period of time to charge.
If a resistor is placed in series with the capacitor, the timing will
increase. The chip detects the rising and falling voltage on the
capacitor. When the voltage on the capacitor is 2/3 of the supply the
output goes LOW and when the voltage falls to 1/3, the output goes
HIGH.
We can also do other things with the chip such as "freezing" or halting
its operation, or allowing it to produce a single HIGH-LOW on the
output pin. This is called a "ONE-SHOT" or MONOSTABLE OPERATION.
When the chip produces an output frequency above 1 cycle per second,
(1Hz), the circuit is called an OSCILLATOR and below one cycle per
second, it is called a TIMER.
But the chip should not be called a "555 Timer," as it has so many
applications. That's why we call it a "555." (triple 5)
For photos of nearly every electronic component, see this website:
https://www.egr.msu.edu/eceshop/Parts_Inventory/totalinventory.php
You can also search the web for videos showing the 555 in action.
Here are a few: