Low-cost Touch Sensitive Switch

While experiment with a high gain transistor it may be noticed the transistor gets saturated by just touching its base. Here is a single, low-cost touch switch based on this idea. The 50Hz hum present in our body is the key of this circuit.

BEL BC557B pnp transistor has been chosen for this circuit. All the transistors used in this circuit are of pnp type. The circuit is basically a RS flip-flop formed by T₃ and T₄. Set and reset inputs are buffered by T₁ and T₂. Set and Reset inputs are buffered by T₁ and T₂. On switching the power supply on the bases of T₃ and T₄ become positive simultaneously. But due to slight difference in characteristics of T₃ and T₄ (since it is not possible to make perfectly matched transistor) one of the transistor become unsaturated. Transistor T₅ is used as relay driver transistor.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁, R₃, R₆, R₇, R₉ = 10 KΩ

R₂, R₄, R₅, R₈ = 220 KΩ

Semiconductors

T₁ – T₅ = BC557B

D₁ = 1N4001

Miscellaneous

RL₁ = 12V/200Ω relay

Touch plate

Automatic guest detector with electronic eye

Electronic eye:


Electronic eye has much use in this electronic age. Also Known as magic eye. It can be used as an automatic guest indicator at the door, If fitted on the bottom of the door entrance. Once it is installed at the door there is no need to install a call bell. It can also be used at homes or in banks as a burglar alarm.

Circuit Diagram of Electronic Eye

     Fix the LDR to the wooden door or a locker to be protected in such a manner that when anybody tries to open it, a shadow falls on the LDR and the circuit gets activated and produce a pleasant sound through the buzzer.
This electronic eye circuit uses NOT gate from CMOS I.C CD 4049. CD 4049 contains 6 independent NOT gate in one package; we have used here (a) one only. NOT gate output goes high(1) when the input pin 3 is at lower then 1/3rd level of the supply voltage. Conversely the output goes low (0) when it is above 1/3rd level. So small change in the voltage of pin-2 is enough to change the level of output (pin-3) from 1 to 0 and 0 to 1. The output has only two states high and low and can not remain in any intermediate stage. It is powered by a 9V battery for portable use. The circuit is economic in power consumption. Pin 1 is connected to the positive supply and pin 8 is grounded.
To detect the present of an object we have used LDR and a source of light. LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has resistance of about 1 mega ohm when in total darkness, but a resistance of only about 5k ohms when brightness illuminated. It responds to a large part of light spectrum.
We have made a potential divider circuit with LDR and 220 KΩ resistance connected in series. We know that voltage is directly proportional to conductance so more voltage we will get from this divider when LDR is getting light and low voltage in darkness. This divided voltage is given to input of NOT gate.
As soon as LDR gets dark the voltage of input not gate drops 1/3rd of the supply voltage and pin 2 gets high and LED or buzzer which is connected to the output gets activated.

 Advantage of using Logic gate is that data can be easily send to other digital interface device ie one can easily fed data to computer using parallel port or for further processing .

Automatic Fan Controller

Hear is a simple Circuit to automatically switch ON and control a speed of a Fan. For the simplicity of the circuit  we have not included control to threshold level.


























                                         Circuit Diagram of Automatic Fan Controller

Working: this project uses IC LM35 as a sensor for detecting accurate centigrade temperature. Output voltage of this sensor is linearly proportional to the Celsius (Centigrade) temperature. This sensor use the fact that- as temperature increases, the voltage across a diode increases at a known rate. Output of IC is 10mv/degree centigrade for eg if temperature is 45 degree then the output of sensor will be 450mv or 0.45V

 Output data of sensor is applied to a current amplifier circuit and feed to a low power DC motor. We have made current amplifier by using a general purpose NPN transistor. I have used BC548 as shown in the circuit diagram. If you are using other NPN transistor then make sure about pin configuration. Transistor will start conducting when base voltage reaches to 0.40 V (40 Degree). You will see fan start to rotate  and at 0.60V (60 degree) it will be at full speed. At this voltage transistor is fully  conducted means resistance is low .

Part List:

IC LM35, Any general purpose NPN Transistor eg BC548, Low power DC Motor you can easily get from old thrown DVD Player or Tape Recorder, small fan Blade, 10 Ohms or 4.7 ohms resistance, battery etc

Clap Switch to ON/OFF electrical appliances

  Here is a Hobby Circuit for electronics hobbyists that can switch on & off a light, Fan, Radio etc. by the sound of clap. The sound of clap is received by a small microphone that is shown biased by resistor R1 in the circuit. The microphone changes sound wave in to electrical wave which is further amplified by Q1. Transistor Q1 is used as common emitter circuit to amplify weak signals received by the microphone. Amplified output from the collector of transistor Q1 is then feed to the Bistable Multivibrator circuit also known as flip-flop circuit.

    Flip flop circuit is made by using 2 Transistor, in our circuit Q2&Q3. In a flip-flop circuit, at a time only one transistor conduct and other cut off and when it gets a trigger pulse from outside source then first transistor is cutoff and 2nd transistor conducts. Thus output of transistor is either logic-0 or logic-1 and it remains in one state 0 or 1 until it gets trigger pulse from outer source.

    The pulse of clap which is a trigger for flip-flop which makes changes to the output which is complementary (reverse). Output of flip-flop which is in the low current form is unable to drive relay directly so we have used a current amplifier circuit by using Q4 which is a common emitter circuit. Output of Q4 is connected to a Relay (Electromagnetic switch) which works like a mechanical switch and it becomes easy for connecting other electrical appliance.

    The relay contact is connected to the power line and hence turns on/off any electrical appliance connected all the way through relay.

Picture of Clap Switch Project

Circuit Diagram of clap Switch

         Clap Switch Part List:- 

Resistors

R1=15KΩ, R5,R6=1.5KΩ
R2,R11,R12=2.2MΩ, R13=2.2KΩ
R3=270KΩ, R4=3.3KΩ
R7,R8=10KΩ, R9,R10=27KΩ
Capacitors
C1=1000µf/16v
C2=.01µf,C3,C4=.047µf
Semi Conductors
Q1,Q2,Q3= BC548
D2,D3,D4= IN 4148
D1,D5=IN 4007, Q4=BC368
Misc
T1=12v/500mA Transformer
Mic= Condenser Microphone
K1= 12V Relay, B1= Bulb or Load

Laser Security System

A really easy and cool electronics project and lots of fun to play with once it finished.Its basically a laser tripwire but has a large application quotient in our everyday life's! so all you teenagers and mad scientists go out there and make your rooms and labs intruder proof :D 

PARTS REQUIRED:
• Breadboard / Perf-board
• Transistor- BC 109 (or any equivalent general purpose NPN transistor) 
link to the datasheet of BC109 :http://alltransistors.com/pdfview.php...
• Wires for connecting
• 9 volt battery
• 9 volt battery clip
• 10k ohm resistor
• LDR- mine was 8k ohm

HOW THE CIRCUIT WORKS:
This electronic circuit uses a transistor to detect light falling on the LDR (light dependent resistor) to activate or deactivate an alarm (or any kind of electronic component). The two resistors (the resistor and the LDR) are connected in series and the common point between them is connected to the base of the transistor, making a potential divider. It uses the property of "threshold voltage" of the transistor to trigger the alarm. This means that we can set a minimal amount of light intensity to trigger the alarm. I have set it to the intensity of sunlight as the minimal. This means that, it won't trigger indoors in ambient light but only when there is a light of high intensity (like a laser). To set your own intensity or if you don't a LDR that is working with the current specifications then just replace the resistor with a potentiometer (or other kind of variable resistor) of something like 30k ohm. Then keep changing the value until you get the desired result.
A more scientific method will be to see the reading (resistance) of the LDR in the desired light. Check the threshold voltage from the datasheet and then used the potential divider formula to calculate the required resistance of the 2nd resistor. 

Note: The relay is only used for simplicity. The output can also be controlled by power transistors, to control any other device.

This blog is created for the electronic based discussions and all the doubts will be cleared and every question will have a solution with in an hour u may leave ur questions below and check this blog for the updates of simple way of using electronics in making few devices and practicals.

Robot in Simple way

How to Build a Simple Robot – Beetle Robot

Do not miss the new up-to-date and detailed How to Build a Robot – Grand Tutorial Series.

The following article will show you how to build a simple robot, called “The Beetle Robot”, created by Jerome Demers. It’s great for beginners and is easy to do. Before starting, I suggest you to read the complete tutorial below. This will greatly lower the chances of you making a mistake. This is the Beetle Robot v. 3 you are going to build:

Tools Needed:

• soldering iron ( here’s a helpful tutorial on soldering )
• electronic solder
• diagonal cutter
• Mini glue gun

Components for the robot

• 2x – small DC motors
• 2x – small paperclips
• 2x – big paperclips
• 2x – batteries AAA or AA
• 1x – AA battery holder or AAA battery holder
• 1x – 2 cm of heat shrink
• 1x – wooden pearl (for the caster)
• 1x – meter of electric wire
• 2x – Sub-mini lever SPDT switches
  

Here are the serial numbers of the components and tools from RadioShack .

Component

Number

soldering iron	64-2184
electronic solder	64-006
diagonal cutter	64-2951
1.5 Volts motor	273-223
battery holder	270-398
SPDT switch	275-016

Most of the components can be bought for much cheaper at Digi-Key, Jameco, or similar. At RobotShop, you can find the dual AA battery holder and the small DC motor. You can also find these components at any good electronic component store. Here are all the parts needed for the construction the beetle robot:
1. Cut the electric wire in pieces of 6 cm each, 13 times.
Strip 1 cm at each end.
2. Regroup all the components.

3. Solder each wire to each components except the two batteries.
4. Take the battery holder and make a connection to the connection.
This will give a third connection.See picture below.
The blue wire is the third connections
5. Turn the battery holder up side down so the batteries point to the ground. Glue the two switches on the battery holder in a V form.
6. Glue the motor beside each switch so that the shaft touches the ground
7. Take the big paperclip and make the caster like the picture below.
You can make a nice looking caster or a normal one
I prefer the nice one
8. How to make the connection

9. Take the small paper clip and bend them to make antenna.
Glue them to the switches and don’t put to much glue.
Add 1 cm of heat shrink to the shaft of each motor.
10. Add the batteries in the battery holder and put it on a flat surface to see your creation take life. Congratulations!