In most general terms, this system’s behavior is sufficiently explained by
using only two of its states can be Voltage(more than x volts or less?),distance covered(more
than 2.5 km or less?], true-false or weight of an elephant(will my weighing
machine withstand it?) )
NOTE: The numbering scheme of IC pins will be explained in the lab session. Different ICs may have the different numbers of pins.
LED (Light Emitting Diode) is frequently used to display the outputs at various stages of the circuit. It is essentially a Diode with the energy released in the form of photons due to electron transitions falling in the visible region. Hence normal diode properties apply to it. It glows only in fwd bias mode i.e. with p junction connected to +ve voltage and n junction to negative.
Diodes are essentially low power devices. The current through the LED should be less than 20mA. Hence always put a 220-ohm resistor in series with the LED.
Never forget that LEDs consume a significant amount of power of the outputs of the ICs (CMOS-based). Hence it is advisable to only use them for checking the voltage level (high or low) and then
remove them.
Note that although in every case, all the intermediate states ARE POSSIBLE
AND DO EXIST,
our points of interest are such that we don’t require their explicit
description. In electronic
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- Assigning States
There is no specific fixed definition of logic levels in electronics. The
most commonly used level
the designation is the one used in CMOS and TTL (transistor logic) families:
Logic high –> designated as ‘1’
A logic low –> designated as ‘0’
Where high and low are actually ‘higher’ and ‘lower’ with respect to a
reference voltage level (ideally taken as 2.5V)
- Number Systems in digital electronics
1. Binary: Only ‘0’ and ‘1’.
2.Hexadecimal: 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
- Types of Digital Circuits
Combinatorial Circuits: In these circuits, the past states are immaterial
and the output depends only upon the present state. Example logic gates
Sequential circuits: In these circuits, the next state is completely
determined by the past states. Hence these follow a predictable structure
and essentially require a timing device. Ex. counters, flip flops.
- Clock: The building block of a sequential circuit
A clock is simply alternate high and low states of voltage with time i.e.
essentially a square wave.
Important terms related to the clock are its duty cycle and its frequency:
Important terms related to the clock are its duty cycle and its frequency:
- Logic Gates: The building block of a combinatorial circuitry
These are essentially combinatorial circuits used to implement logical
Boolean operations like AND, NAND, OR, XOR, and NOT. NOT and NAND are called
universal gates as any other gate can be formed using either of them!
Table of Logic Gates
Practical Circuiting Elements
- Resistors:
- Capacitor:
The 2 types of capacitors we frequently use in circuits are ceramic and
electrolytic capacitors. While ceramic capacitors do not have a fixed
polarity; electrolytic capacitors should be connected in their specified
polarities only else they might blow off! This polarity is usually
provided on the side of the capacitors ‘corresponding leg.
- Breadboard:
This is the base used for setting up the circuit. This has embedded metal
strips in it that form a grid of connections inside its body. This allows us
to take multiple connections from a single point without any need for
soldering/disordering as in PCBs. It is always a good habit to test the
circuit on
breadboard before making it on a PCB.
- Integrated Circuits (IC)
NOTE: The numbering scheme of IC pins will be explained in the lab session. Different ICs may have the different numbers of pins.
- LED
LED (Light Emitting Diode) is frequently used to display the outputs at various stages of the circuit. It is essentially a Diode with the energy released in the form of photons due to electron transitions falling in the visible region. Hence normal diode properties apply to it. It glows only in fwd bias mode i.e. with p junction connected to +ve voltage and n junction to negative.
Diodes are essentially low power devices. The current through the LED should be less than 20mA. Hence always put a 220-ohm resistor in series with the LED.
Never forget that LEDs consume a significant amount of power of the outputs of the ICs (CMOS-based). Hence it is advisable to only use them for checking the voltage level (high or low) and then
remove them.
