EFY Microcontroller_Based_Projects.pdf

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12 Exciting Microcontroller Projects

SPecial iSSue

Microcontroller

Based Projects

For You

Cellphone-

Operated Land

Rover

Speedometer-

Cum-Odometer

For Motorbike

Solar Charger

For Dusk-To-

Dawn Use

Digital

Thermometer-

Cum-Controller

Automated

Line-Following

Robot

Table of

Contents

Water-Level Controller-Cum-Motor Protector.............................

Cellphone-Operated Land Rover...................................................

Speedometer-Cum-Odometer For Motorbike..............................

Solar Charger for Dusk-to-Dawn Use...........................................

Sophisticated But Economical School Timer.................................

Remotely Programmable RTC-Interfaced

Microcontroller for Multiple Device Control................................

Remote-Controlled Digital Audio Processor.................................

AT89C51-Based DC Motor Controller........................................

Secured Room Access System........................................................

Digital Thermometer-Cum-Controller...........................................

Interfacing a Graphics LCD with the Microcontroller..................

Automated Line-Following Robot ................................................

10.

11.

12.

Water-level Controller-

Cum-motor ProteCtor

any a time we forget to switch off the motor pushing water into the overhead tank (OHT) in our

households. As a result, water keeps overflowing until we notice the overflow and switch the pump off.

As the OHT is usually kept on the topmost floor, it is cumbersome to go up frequently to check the

water level in the OHT.

Here’s a microcontroller-based water-level controller-cum-motor protector to solve this problem. It controls

‘on’ and ‘off ’ conditions of the motor depending upon the level of water in the tank. The status is displayed on an

LCD module. The circuit also protects the motor from high voltages,

low voltages, fluctuations of mains power and dry running.

Parts List

Semiconductors:

IC1

IC2

Fig. 1 shows the circuit of the microcontroller-based water-level con-

IC3

troller-cum-motor protector. It comprises operational amplifier LM324,

IC4

T1-T4

microcontroller AT89C51, optocoupler PC817, regulator 7805, LCD

module and a few discreet components.

D1-D14

Circuit description

The AT89C51 (IC2) is an 8-bit microcontroller with four ports (32

I/O lines), two 16-bit timers/counters, on-chip oscillator and clock cir-

cuitry. Eight pins of port-1 and three pins of port-3 are interfaced with

data and control lines of the LCD module. Pins P3.0, P3.1 and P3.6

are connected to RS (pin 4), R/W (pin 5) and E (pin 6) of the LCD,

respectively. Pin EA (pin 31) is strapped to Vcc for internal program

executions. Switch S2 is used for backlight of the LCD module.

Power-on-reset is achieved by connecting capacitor C8 and resistor

R14 to pin 9 of the microcontroller. Switch S1 is used for manual reset.

The microcontroller is operated with a 12MHz crystal. Port pins

P2.0 through P2.2 are used to sense the water level, while pins P2.3 and

P2.4 are used to sense the under-voltage and over-voltage, respectively.

Pin P3.4 is used to control relay RL1 with the help of optocoupler IC3

and transistor T5 in the case of under-voltage, over-voltage and differ-

ent water-level conditions. Relay RL1 operates off a 12V supply. Using

switch S3, you can manually switch on the motor.

The LM324 (IC1) is a quad operational amplifier (op-amp). Two of

its op-amps are used as comparators to detect under- and over-voltage.

In normal condition, output pin 7 of IC1 is low, making pin P2.3 of

IC2 high. When the voltage at pin 6 of N1 goes below the set reference

voltage at pin 5 (say, 170 volts), output pin 7 of N1 goes high. This high

output makes pin P2.3 of IC2 low, which is sensed by the microcon-

troller and the LCD module shows ‘low voltage.’

In normal condition, pin 1 of N2 is high. When the voltage at pin 2

of N2 goes above the set voltage at pin 3, output pin 1 of N2 goes low.

This low signal is sensed by the microcontroller and the LCD module

shows ‘high voltage.’

Presets VR1 and VR2 are used for calibrating the circuit for under-

Microcontroller-Based Projects

LM324 quad op-amp

AT89C51 microcontroller

PC817 optocoupler

7805, 5V regulator

BC548 npn transistor

SL100 npn transistor

1N4007 rectifier diode

Resistors (all ¼-watt, ±5% carbon):

R1, R2, R7,

R11, R12

R3, R9

R4, R5, R8

R10

R13

R14

R15-R17

R18-R20

R21, R22

RNW1

VR1, VR2

VR3

Capacitors:

C1-C3

C5, C6

1-kilo-ohm

560-kilo-ohm

2.7-kilo-ohm

330-ohm

470-ohm

100-ohm

10-kilo-ohm

100-kilo-ohm

2.2-kilo-ohm

33-ohm

10-kilo-ohm resistor

network

- 470-ohm preset

- 10-kilo-ohm preset

1000µF, 35V electrolytic

220µF, 16V electrolytic

33pF ceramic disk

100µF, 35V electrolytic

10µF, 16V electrolytic

Miscellaneous:

RL1

TAL

S2, S3

- 230 AC primary to 12V,

500mA secondary

transformer

- 12V, 1C/O relay

- 12MHz crystal

- Push-to-on switch

- On/off switch

- LCD module (1×16)

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