70 Circuitos

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email Colin Mitchell: talking@tpg.com.au

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50 - 555 Circuits
1 - 100 Transistor Circuits
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100 IC Circuits
For a list of every electronic symbol, see: Circuit Symbols.

For more articles and projects to suitthe hobbyist: see TALKING ELECTRONICS WEBSITE

This e-book covers a number of interesting
They have been presented for a reason.
The original circuits come from an Indian Electronics
Magazine and most of them had faults. Either they were
over-designed, poorly designed or contained a fault.
In the process of bringing these faults and corrections to
you, we havecreated this eBook of 70 Interesting Circuits.
You can lean a lot from other peoples mistakes. Not only will
you remember not to make the same mistake but the
corrections and improvements generally require less
The art of designing a circuit is to make it as simple as
possible and use the least number of components.
But before you put a design into production, get someone
else tolook at it.
Another "set of eyes" will see things differently and maybe
simplify or improve the design.
We have already presented a set of pages called "Spot The
Mistake," showing dozens of faulty circuits and how to check
and test things before releasing them. It is surprising that a
magazine with a readership of over 1,000,000 could publish
items with glaring faults.
The faulty projects inthis collection have a revised circuit
included in the article and you can compare the two designs.
It only takes a minute to see a circuit will not work and a
few more minutes to create a improved design.
This is what we are teaching in this section . . . how to look
at a circuit with a "critical eye" then design an improvement.
This is called REVERSE ENGINEERING and involves the highestlevel of technical skill.
But it is also the fastest way to test a persons skill and the
fastest way to learn.
That's why I consider it to be the most important approach to
Colin Mitchell

AC Detector
Auto Cutout
Battery Monitor
Capacitance Beeper
Constant Current Source
Door Watcher
Electronic Siren

555 Schmitt
10Output LED Sequencer
12v Lamp Dimmer
16 LED Night Rider
Ultrasonic Remote Control

Emergency Light
Increasing the input Impedance
Light Controlled Lamp
Lightening Detector
Moving LEDs
to Index


Here is 10 output LED sequencer. After the last LED is illuminated, the circuit is reset. This circuit is build around readily a
low cost components - a 555 and decadecounter CD4O1 7. The timer IC NE555 is wired as an astable multivibrator that
produces 6Hz clock at its output pin 3. The 4017 is a CMOS decade counter with 10 outputs. Inputs include a CLOCK (Pi
RESET (Pin 15), and a CLOCK INHIBIT (Pin 13). The clock input connects to a Schmitt trigger for pulse shaping and allo
clock rise and fall times (not needed in our case).
The counter advances one outputat the rising edge of the clock signal if the CLOCK INHIBIT line is low. A high RESET s
resets the counter to the zero output. The circuit may be configured for counts less than 10 by connecting RESET to an o
(one after the desired count). Thus, a five stage sequencer can be made by connecting pin 15 to pin 1. A CARRY-OUT si
12) can be used to clock subsequent stages in a multi-device countingchain.
The output from 1C2 pin 3 is connected to clock pin (pin 14) of the IC3 for sequencing operations. NPN transistors Q1- Q
used to increase the output current for the LEDs which is set by the common 150 ohm resistor. In the circuit, only one of t
outputs is HIGH at any one time and the output advances by one count with every clock pulse.

But the circuit above is poorly designed.
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