Bluetooth based home automation system

Monday 3 March 2014
This project is a fine combination of Android mobile technology and embedded system. An application should be installed on android mobile handset to control various home appliances. User can send commands using that application. Wireless controlling technique used in this project is Bluetooth technology. This project consists of a Bluetooth receiver. This Bluetooth device is connected to the circuit which has a decoder. This decoder sends code for respective command sent by user. Then the respective device connected to the circuit will be turned on or off depending on the command given.

Block Diagram:

Transmitter / Controlling unit

Description in detail:
This project mainly consists of following blocks:
1) Android mobile
2) Bluetooth receiver unit
3) Microcontroller
4) LCD Display
5) Relays
6) Output devices
Applications and Advantages:
1. Home automation – This project can be used to control various Home Appliances
2. We can control device from a long distance, thus it gives ease of access.
3. Faster operation and efficient.                                                                                                        
4. No need to carry separate remote or any other controlling unit.
Future Development:
1. We can interface sensors to this project so that it can monitor some parameters

APP interface:

working video:

line follower robot-with and without microcontroller.

Wednesday 2 October 2013
it really nice experience to make line follower to this weekend .
we can make it either by  using micro controller or with out micro controller.
first we will see without making microcontroller :-
steps involving to make this:
we should make ir transmitter and reciever.
(black colour strip is good observer of IR where  white colour is good reflector.)

so,when line follower robot passes over the black strip the light fallen from IR transmitter is not reflected back and when it passes over the white surface IR transmitter receives the signal.

when passes over black surface ir signal absorbed
so, ir RX doesn't receives any signal and viceversa .
assume that we attached the two pair of IR sensors placed in front of the robot .see the below set of conditions.
sensors are connected to the pin 1 and voltage divider is attached to the pin 2 whose voltage is maintained at 2.5 v
we use comparator ,where pin 1 is attached to the out put of the ir receiver and pin 2 is attached to the votage divider.

when the voltage of the sensor is above the 2.5v the output is 5v and when the voltage is less than 2.5v the output will be 0v.

case 1:-

when it passes over the black surface the IR  RX gets 0v .which is connected to the pin 1 of the comparator
so output will be 0v
case 2:-
when it passes over the white surface the IR RX gets >2.5 and <5. so the output of the comparator will be high .

To be more accuracy we will use 3 set of  IR pairs whose receiver ends are connected to comparator which intern connected to logic gates to obtain the below table.

say A is left sensor B is center sensor C is right sensor.

lets us consider the case L+:
k=map for the case L+

from the table,  L+=A'(B'C+BC)+A'(BC+BC')+BC
circut diagram for the case L+:

similarly for the case L-,R+,R-.we can obtain the circuit diagram.

to drive the motors we will use l293d ic (which is like h-bridge):-

the outputs of L-,L+,R-,R+ is connected to pin 4,5,6,7 respectively.and 12v supply is given to l293d.

controlling motors,servos,steppers

Wednesday 18 September 2013
have u ever wonder,how we can control robots to move right left straight  back.with out using steering in bots. i'll show u how we can control the direction of the bots .first we need to know abt h-brige.lets do that.


As you can see in the image, the circuit has four switches S1, S2, S3 and S4. Turning these switches ON and OFF can drive a motor in different ways.
  1. Turning on Switches S1 and S2 makes the motor rotate clockwise
  2. Turning on Switches S2 and S3 makes the motor rotate anti-clockwise

  1. Turning on Switches S1 and S2 will stop the motor (Brakes)
  2. Turning off all the switches gives the motor a free wheel drive
  3. Lastly turning on S1& S3 at the same time or S2 & S4 at the same time shorts your entire circuit. So, do not attempt this
  • HOW TO CONSTRUCT H-bridges for DC motors:

  1. type 1:-(4 inputs to control 1 motor)
H-bridges can be built from scratch using relays, mosfets, field effect transistors (FET), bi-polar junction transistors (BJT), etc. But if your current requirement is not too high and all you need is a single package which does the job of driving a small DC motor in two directions, then all you need is a L293D IC

A,B,C,D can be connected to micro controller and we can control the motors according to the program.
simple push switch connected between pt A and B and gnd ...similarly rest of the pt .by pushing the switches we can control the direction of the motor`

2.   type 2:-( 2 inputs to control 1 motor)

just by two switches we can control clock wise and anticlockwise rotation of the motors
3.    type 3:-( 4 inputs to control 2 motor)

Construction using l293d ic (4 inputs controlling 2 motors) :

L293D construction is similar to the h-bridge controlling 2 motors but using l293d is more preferable as it was so easy and occupies very few space in circuit
here pin 13 ,pin 12,pin 11,pin 10 are synonymous to pin A,B,C,D in above H-bridge controlling 2 motors
google for the datasheet of the L293D ic for more information.

how to control servo motors: 

servos works based on pwm(pulse width modulation)
so it requires the pulses along with voltage.the best way to control the servo are using the 555 timmer.(click the link to know abt 555 timmer).

second year projects

Tuesday 17 September 2013

  • blood oximeter (heart beat measuring from finger  )
 This project describes a technique to measure  heart rate through fingertip. The blood volume inside a fingertip slightly changes with heart beat as the blood is being pumped. This change in blood volume inside the finger artery can be detected with a simple optical sensor system and can be further amplified using appropriate signal conditioning circuit to generate a pulse of magnitude +5V. These pulses can be later counted by a micro controller to display the measured heart rate .
Circuit diagram: 

  • audio DJ mixer:
Circuit diagram:

  • distance counter while ur walking:

This circuit measures the distance covered during a walk. Hardware is located in a small box slipped in pants' pocket and the display is conceived in the following manner: the leftmost display D2 (the most significant digit) shows 0 to 9 Km. and its dot is always on to separate Km. from hm. The rightmost display D1 (the least significant digit) shows hundreds meters and its dot illuminates after every 50 meters of walking.
A beeper (excludable), signals each count unit, occurring every two steps. A normal step was calculated to span around 78 centimeters, thus the LED signaling 50 meters illuminates after 64 steps (or 32 operations of the mercury switch), the display indicates 100 meters after 128 steps and so on.
For low battery consumption the display illuminates only on request, pushing on P2. Accidental reset of the counters is avoided because to reset the circuit both push buttons must be operated together. Obviously, this is not a precision meter, but its approximation degree was found good for this kind of device. In any case, the most critical thing to do is the correct placement of the mercury switch inside of the box and the setting of its sloping degree.
Circuit diagram:

voltage regulators

Friday 6 September 2013
some times ,u might have 9v battery and u need only 5v to run ur load.then this voltage regulators place a crucial role.
normally 78xx series ics are used to regulate the voltages
here is the list of voltage regulator ics
for an example:
take 7805ic
minimum i/p is 7.3v and o/p is 5v
for the voltage above 7.3 the o/p will be equal to 5v
for an i/p voltage lesser than 5v o/p will be equal to input.
google the datasheet of the ics ,before u use them in ur project**

motors and batteries

Saturday 31 August 2013

two things to be taken in to consideration while purchasing the motors,they are
speed and torque
speed will be measured in RPM (rotation per minute),more is the rpm more will be the speed.
the amount of the force applied by the motors will be based on the torque of the motor

it means more the toque of the motors ,it will apply more force.
torque will increase by adding the gears to the motors
usually we will prefer dc motors ,stepper motors,brush less motors, servo motors.

 1.servo motors are preferred to the arms movements of the robot
 PWM signals are sent to the black yellow wire and vcc to red and gnd to black.
 PWM signals can be generated from 555 ic.
normally servo rotates from 0 to 180 degree ,but by changing the internal gears we can make it rotate 360 degree
 it provides high toque with less rpm.(which are preferred to arm movements)
2.DC motors:
  dc geared motors are preferred by most of the hobbyist as  they provide good torque with high speed (rpm) at low price
normally 300 to 500 rpm with torque (2-3 kg cm)is preferred for robots.


555 (A to z)

Thursday 22 August 2013

  • The 555 Integrated Circuit (IC) is an easy to use timer that has many applications. It is widely used in electronic circuits and this popularity means it is also very cheap to purchase.
  • A 'dual' version called the 556 is also available which includes two independent 555 ICs in one package. 

1.Pin configuration

Pin 1 (Ground):
Connects to the 0v power supply. 
Pin 2 (Trigger):
Detects 1/3 of rail voltage to make output HIGH. Pin 2 has control over pin 6. If pin 2 is LOW, and pin 6 LOW,  output goes and stays HIGH. If pin 6 HIGH, and pin 2 goes LOW, output goes LOW while pin 2 LOW. This pin has a very high impedance (about 10M) and will trigger with about 1uA. 

Pin 3 (Output):
(Pins 3 and 7 are "in phase.") Goes HIGH (about 2v less than rail) and LOW (about 0.5v less than 0v) and will deliver up to 200mA. 

Pin 4 (Reset):
Internally connected HIGH via 100k. Must be taken below 0.8v to reset the chip. 

Pin 5 (Control):
A voltage applied to this pin will vary the timing of the RC network (quite considerably). 

Pin 6 (Threshold):
Detects 2/3 of rail voltage to make output LOW only if pin 2 is HIGH. This pin has a very high impedance (about 10M) and will trigger with about 0.2uA. 

Pin 7 (Discharge):
Goes LOW when pin 6 detects 2/3 rail voltage but pin 2 must be HIGH. If pin 2 is HIGH, pin 6 can be HIGH or LOW and pin 7 remains LOW. Goes OPEN (HIGH) and stays HIGH when pin 2 detects 1/3 rail voltage (even as a LOW pulse) when pin 6 is LOW.  (Pins 7 and 3 are "in phase.") Pin 7 is equal to pin 3 but pin 7 does not go high - it goes OPEN.  But it goes LOW and will sink about 200mA. 

Pin 8 (Supply):
Connects to the positive power supply (Vs). This can be any voltage between 4.5V and 15V DC, but is commonly 5V DC when working with digital ICs.

2. modes of operation
The 555 has three main operating modes, Monostable, Astable, and Bistable. Each mode represents a different type of circuit that has a particular output. 

Astable mode 

An Astable Circuit has no stable state - hence the name "astable". The output continually switches state between high and low without without any intervention from the user, called a 'square' wave. This type of circuit could be used to give a mechanism intermittent motion by switching a motor on and off at regular intervals. It can also be used to flash lamps and LEDs, and is useful as a 'clock' pulse for other digital ICs and circuits. 


Monostable mode 

Monostable Circuit produces one pulse of a set length in response to a trigger input such as a push button. The output of the circuit stays in the low state until there is a trigger input, hence the name "monostable" meaning "one stable state". his type of circuit is ideal for use in a "push to operate" system for a model displayed at exhibitions. A visitor can push a button to start a model's mechanism moving, and the mechanism will automatically switch off after a set time. 


Bistable Mode (or Schmitt Trigger) 

Bistable Mode or what is sometimes called a Schmitt Trigger, 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. This type of circuit is ideal for use in an automated model railway system where the train is required to run back and forth over the same piece of track. A push button (or reed switch with a magnet on the underside of the train) would be placed at each end of the track so that when one is hit by the train, it will either trigger or reset the bistable. The output of the 555 would control a DPDT relay which would be wired as a reversing switch to reverse the direction of current to the track, thereby reversing the direction of the train. 


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