Digital electronics:some integrated circuits and their implementation

Some integrated circuits and their implementation:

some ics and their implementation

In previous post i talked about the basics of digital electronics,if you don't see this you can read this post here.Now we discuss about some integrated circuits and their implementation according to the schedule sequentially.So let's learn-

555 timer IC:

The 555 is a single chip version of a commonly used circuit called a multivibrator.

The IC used in a variety of timer,pulse generation, and oscillator applications.
The 555 timer has three modes- monostable,astable and bistable.

555 timer ic pinout

Monostable mode:

Monostable or 'one shot' mode,produces a single pulse of a set length in response to a trigger input.Here's the formulas written below to find out the time (T),capacitance (c) and resistance (R)-

       T=1.1RC

       C= T/1.1R

       R= T/1.1c

Monostable mode of 555 timer IC

Astable mode:

Astable or free running mode, has no stable state and output switches between high and low.Producing a square wave output.We can set the clock frequency and duty cycle D by the formulae:

t1=0.693(R1+R2)C

t2=0.693R2C

f=1.44/(R1+2R2)C

Duty cycle= (R1+R2)/(R1+2R2)×100

T=t1+t2

  =0.693(R1+2R2)C

Astable mode of 555 timer IC

Bistable mode:

Bistable or schmitt trigger mode, has two stable states-high and low,taking the trigger input low makes the output of the circuit go into the high state taking the reset input low makes the output of the circuit go into the low state.

Bistable mode 555 timer

4029 counter IC:

4017 counter IC pinout

One of the most common requirements in digital equipment is counting. And the most common counting requirement has to do with time. From a basic digital clock (which is incorporated into most digitally-controlled appliances) to interval timers and event counters, the need for counting circuits is very great.

Counters are required for various counting ranges and in all sorts of circumstances. A simple digital clock, for example, requires a decimal counter for the units positions of seconds and minutes, but must count only from 0 to 5 (modulo-6) for the tens positions of minutes and seconds. Hours digits require special handling, since the two-digit output must count either from 1 to 12 or 0 to 23, depending on how we want the display to appear. Some clocks skip the 0 to 23 military display and run from 1 to 24 in that mode. And some simple clocks make no effort at that, or to distinguish between AM and PM.

No matter how the hours are handled, the basic element required to make any digital clock work is the counter circuit. Indeed, counters are so important in so many applications that many different kinds of counter ICs have been designed for both TTL and CMOS logic families. Some count up for clocks and time intervals; others count down to show time remaining until some event. Some are specifically designed to count in decimal mode, while others count in binary, and still others have selectable counting ranges. The list of capabilities and options is quite large, leaving the circuit designer with only the task of selecting the particular IC that best suits the need.

Hence 4029 can also be used as a memory element that remembers its immediate previous state.

Pin description:4017 counter IC-

Pin description:4017 counter

7447 IC: BCD to 7 segment display decoder:

For displaying the number in the counter output on a seven segment display (i.e. 7 LEDs making up a figure of ‘8’ as in a general calculator. See fig.) we need to decode the 4 bits and match them to the 7 pins for lighting the LEDs corresponding to the number. This work is done by 7447.

7447 ic and seven segment display pinout

Pin Description of 7447 IC:

Here's the pin description of 7447 IC scheduled below-

7447 pin description

LDR (Light Dependent Resistor):

Light Dependent Resistor (LDR) or photo resistor is a device that acts like a resistance and its resistance varies with the intensity of light incident on it. In this device, if photons of sufficient energy fall on it, the resistance drops drastically as the electrons in the semiconductor are able to jump from the valence band to the conduction band and are available for conduction.The LDRs used  are mostly responsive to visible light. The resistance might drop from as high as 1MΩ in the dark to 1 k Ω in bright light.

LDR pinout:The coiled portion of LDR is responsive to light

Operational Amplifier (Opamp):

op-amp is a very important device used in everyday electronics .It is essentially a differential amplifier with a very high gain of the order of 10^5! By differential amplifier I mean that it amplifies the difference of 2 signals and gives the output.

Opamp equation:

Vout= A (V+ - V- ), where A is the gain of the order 10^5

Op-amp pinout

Ironically, this high gain in open loop makes it impossible to use it as a general purpose differential amplifier directly

Op-amp as a comparator:

The Op-amp comparator compares one analogue voltage level with another analogue voltage level, or some preset reference voltage, VREF and produces an output signal based on this voltage comparison. In other words, the op-amp voltage comparator compares the magnitudes of two voltage inputs and determines which is the largest of the two.

7805 Voltage Regulator:

7805 IC pinout

7805 voltage regulator is used to get +5 V output out of a higher voltage supply (7.5V-20V).We use adapter’s supply to generate +5V here. Connect the gnd and +12V of adapter to the pins as shown and get +5V directly as an output out of the 3rd pin. Current up to 0.5 A can be obtained from this regulator without any significant fall in voltage level.

7805 circuit diagram

*Use 2 capacitors of value say 0.1µF to filter the noise in the input and output of regulator’s supply as shown. Also put a capacitor of 10 – 100 uF at output to take care of the low frequency dip in the voltages.