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
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
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 - but
it still takes 10mA while "sitting around".
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)
Another thing you have to be aware of is the voltage on output pin 3. It
is about 1-2v LESS THAN rail voltage and does not go to 0v (about 0.7v
for 10mA and up to 1900mV for 200mA sinking current).
For instance, to get an output swing of 10v you will need a 12.6v
supply. In "electronic terms" the 555 has very poor sinking and
One way to understand how the chip operates is to remember that pin 7
goes LOW when pin 3 (the output pin) goes LOW. When pin 3 goes HIGH, pin
7 goes "open circuit" (it does not go HIGH - it goes HIGH IMPEDANCE).
When in 4 is taken LOW, the chip stops operating, but it still takes
For photos of nearly every electronic component, see this website:
You can also search the web for videos showing the 555 in
Here are a few:
Making A 555 LED Flasher – Video Tutorial
Three 555 LED Flasher
Fading LED with 555 timer
Each website has lots more videos and you can see exactly
how the circuits work. But there is nothing like building the circuit
and that's why you need to re-enforce your knowledge by ACTUAL
Learning Electronics is like building a model with Lego bricks. Each
"topic" or "subject" or "area" must be covered fully and perfectly, just
like a Lego brick is perfect and fits with interference-fit to the next
block. When you complete this eBook, you can safely say you will have
mastered the 555 - one more "building block" under your belt
and in the process you learn about DC motors, Stepper motors, servos, 4017
chips, LEDs and lots of other things. Any one of these can take you off
in a completely different direction. So, lets start . . .
To save space ( and get everything on a single page) we have not provided lengthy explanations of how any of the
circuits work. This has already been covered in TALKING ELECTRONICS
Basic Electronics Course, and can be obtained on a
CD for $10.00
to anywhere in the world). See Talking Electronics website (http://www.talkingelectronics.com) for more
details on the 555 by clicking on the following
while others are freely available on the web. But this eBook has brought
everything together and covers just about every novel 555 circuit. If
you think you know everything about the 555, take the
and you will be surprised!
Many of the circuits have been designed by Colin Mitchell:
Reaction Timer Game,
TV Remote Control Jammer, 3x3x3 Cube,
All the schematics in this eBook have components that are
labelled using the System International (SI) notation system. The SI
system is an easy way to show values without the need for a decimal
point. Sometimes the decimal point is difficult to see and the SI system
overcomes this problem and offers a clear advantage.
Resistor values are in ohms (R), and the multipliers are: k for kilo, M
for Mega. Capacitance is measured in farads (F) and the sub-multiples
are u for micro, n for nano, and p for pico. Inductors are
measured in Henrys (H) and the sub-multiples are mH for milliHenry and
uH for microHenry.
A 10 ohm resistor would be written as 10R and a 0.001u capacitor as 1n.
The markings on components are written slightly differently to the way
they are shown on a circuit diagram (such as 100p on a circuit and 101
on the capacitor or 10 on a capacitor and 10p on a diagram) and you will have to look on the internet under
Basic Electronics to learn about these differences.
Here's a 555 built from transistors by
Eric Schlaepfer in honor of
Hans Camenzined, who invented the 555:
A new range of 555 chips have been designed by Talking Electronics to
carry out tasks that normally need 2 or more chips.
These chips are designated: TE 555-1, TE555-2 and the first project to
TE 555-1 is STEPPER MOTOR CONTROLLER TE555-1.
It's a revolutionary concept. Instead of using an old 8-pin TTL
555 chip, you can use a new TE555-1,2,3 8-pin chip and save board
space as well as components. These new chips require considerably less
external componentry and the possibilities are endless. Depending on the
circuit, they can have a number of timing and frequency outputs as well as a
"power-down" feature that consumes almost no current when the circuit is
not operating. See the first project in this series: STEPPER MOTOR CONTROLLER TE555-1.
Stepper Motor Controller project
See also TE 555-2
TE555-3 TE 555-4
A program to work out the values for a 555 in Astable or Monostable mode
is available from Andy Clarkson's website:
(987KB). Name a folder:
Unzip and run "555 Timer setup.exe"
Setup will produce a desktop icon. Click on icon for program. Set the
voltage for the 555 then use the Astable or Monostable tabs to design
your circuit. Read the Help screen to understand the operation of: "Hold
Output" and "smallest."
Here is another 555 calculator by
This calculator will provide a number of component values for the delay you want
or the frequency.
You can specify “10ms” or “4.5kHz” in the text fields.