A Logic AND Gate
is a type of digital logic gate that has an output which is normally at
logic level “0” and only goes “HIGH” to a logic level “1” when ALL of its inputs are at logic level “1”.
The output state of a “Logic AND Gate” only returns “LOW” again when ANY of its inputs are at a logic level “0”. In other words for a logic AND gate, any LOW input will give a LOW output.
The logic or Boolean expression given for a digital logic AND gate is that for Logical Multiplication which is denoted by a single dot or full stop symbol, ( . ) giving us the Boolean expression of: A.B = Q.
Then we can define the operation of a 2-input logic AND gate as being:
Symbol
Truth Table
2-input AND Gate
B
A
Q
0
0
0
0
1
0
1
0
0
1
1
1
Boolean Expression Q = A.B
Read as A AND B gives Q
Follow the link to make And gate demonstration science project
7408 Quad 2-input AND Gate
In the next tutorial about Digital Logic Gates, we will look at the digital logic OR Gate function as used in both TTL and CMOS logic circuits as well as its Boolean Algebra definition and truth tables.
555 timer IC is the cheap, popular and precise timing device
used in various applications. It gets the name from the three 5KΩ resistors
that are used to generate two comparator reference voltages. This IC is
operated as monostable, bistable or astable multivibrater to produce a variety
of applications.
This IC comes with bipolar 8 pins dual in-line package. It
consists of 25 transistors, 2 diodes and 16 resistors arranged to form two
comparators, flip-flops, and high current output stage.
Pin Description
The following is the Pin Description
Pin 1-Ground: It is connected to ground as usual. For the
timer to function this pin should be connected to ground.
Pin 2-TRIGGER: The negative input comparator No 1. A
negative pulse on this pin “sets” the internal Flip-flop when the voltage drops
below 1/3Vcc causing the output to switch from a “LOW” to a “HIGH” state
Pin 3-OUTPUT: This pin also has no special function. This
pin is drawn from PUSH-PULL configuration formed by transistors.This pin gives
the output.
Pin 4-Reset: There is a flip-flop in the 555 IC timer chip.
The output of flip-flop controls the chip output at pin 3 directly. This pin is
connected to Vcc for the flip-flop to stop from hard resetting.
Pin 5-Control Pin: The control pin is connected from the
negative input pin of comparator one. The function of this pin to give the user
the direct control over the first comparator.
Pin 6-THRESHOLD: Threshold pin voltage determines when to
reset the flip-flop in the timer. The threshold pin is drawn from positive
input of comparator1.
Pin 7-DISCHARGE: The discharge pin is connected directly to
the Collector of an internal NPN transistor which is used to “discharge” the
timing capacitor to ground when the output at pin 3 switches “LOW”.
Pin 8-Power or VCC: This pin also has no special function.
It is connected to a positive voltage.
Working Modes OF 555 Timer IC
The 555 timer IC operates in modes
Astable mode
Monostable mode
Bistable mode
Astable mode
Astable mode means there will be no stable levels at the
output. Thus the output will fluctuate from high and low. This character of the
astable output is used as a clock or square wave output for many applications.
Features of 555 timer IC
It operates from a wide range of power supplies ranging from
+ 5 Volts to + 18 Volts supply voltage.
Sinking or sourcing 200 mA of load current.
The external components should be selected properly so that
the timing intervals can be done in several minutes along with the frequencies
exceeding several hundred kiloHertz.
The output of a 555 timer can drive a transistor-transistor
logic (TTL) due to its high current output.
It has a temperature stability of 50 parts per million (ppm)
per degree Celsius change in temperature, or equivalently 0.005 %/ °C.
The duty cycle of the timer is adjustable.
The maximum power dissipation per package is 600 mW and its
trigger and reset inputs has logic compatibility.
Thus, this is all about making of Blinking LED using a 555
timer IC. We hope that you have got a better understanding of this concept.
Furthermore, any queries regarding this topic or 555 timer based projects,
please give your valuable suggestions by commenting on the comment section
below.
The following circuit design explains the design of the
blinking LED with the 555 timer IC. Here in this configuration, the 555
timer IC has connected in an Astable mode of 555 timer operation.
Collect all the required components and place the 555 timer
IC on the breadboard.
Connect pin 1 of a 555 timer IC to the ground. You can find
the pin structure of a 555 timer IC in the circuit diagram shown above.
The longer lead of a polarized capacitor is the positive and
the shorter lead is negative. Connect pin 2 to the positive end of a capacitor.
Connect the negative lead of the capacitor to the ground of the battery.
Now short the pin 2 to pin 6 of the 555 timer IC.
Connect the output pin 3 with the positive lead of the LED
using a 1kΩ resistor. The negative lead of LED needs to be connected with the
ground.
Connect pin 4 to the positive end of the battery.
Pin 5 does not connect to anything.
Connect pin 6 to pin 7 using a 470kΩ resistor.
Connect pin 7 to the positive end of the battery using a 1kΩ
resistor.
Connect pin 8 to the positive end of the battery
Finally, connect the battery leads with the breadboard to
start the power supply in the circuit.
