Simple doorbell Using UM66

Below is a simple circuit of doorbell using UM66. The circuit can be assembled in a general purpose PCB and enclosed in any toys. 

Parts

C1 - 220 µF 10v
VR1 - 100 k pot
VR2 - 10 k pot
T1 and T2 - BC548
IC1 - UM66

Speaker - 8 ohms
Power - 3v

LED Torch with adjustable brightness

LM3914 is used as the basis of a 10 step variable brightness current-regulated white LED torch. This circuit has only four components in the control and regulation circuit: R1,R2, VR1 and LM3914.

Part List

1. IC - LM3914

2. LED1-10 - 10 white led

3. R1 - 620 ohm

4. R2 - 100 ohm

5. VR1 - 100 k pot

6. C 1 - 10 uf 16 v

7. Power - 3-4.5 volt

8. Suitable cabinet and a general purpose PCB.

Dark Sensor

Dark sensor using 2 transistor BC547

When light falls on LDR, its low resistance drives the transistor T1 into conduction. This keeps transistor T2 cut-off due to low base bias. The LED does not get power as long  as ambient light falls on it.

Parts list

1. T1 and T2 - BC 547
2. LDR  -1 nos
3. Resistance  R1 - 1k
4. R2 & R3 - 330 Ohms
5. 6 volt battery

Modifying the above circuit to use with Relay and switch on / off

You can also modify the above circuit in controlling AC appliances. Remove R2 and LED from the circuit and also remove the positive connection to Pole of the relay. Connect the AC bulb or any other appliance as shown



.

Electrical Appliance Protection

This is a simple circuit to protect your electrical appliance during irregular power supply. Normally when power goes off we forget switching off our appliances.Especially in India where power cuts are very frequent we tend to leave our appliances on. In such case there are very high chance of getting it damages by high voltage surge.

The circuit below helps in this and does not switch on unless we press reset button.



Components

1. Diode 1N4007 - 3


2. Capacitor C1 - 1000 25v


3. Relay - 6 V 100


4. Step Down Transformer = 6-0-6 300mA


5. Push to On Switch - 1

Very-short-duration interruptions or fluctuations will  not affect the circuit because of presence of largevalue capacitor. Thus the circuit provides suitable safety against erratic power supply conditions.

LED Flasher using NE555

LED Flasher circuit using NE555 timer IC

• R1, R2, C1 and the supply voltage determine the flash rate. For a variable flash rate, replace R1 with a 1 MΩ pot in series with a 22k resistor.


• The purpose of R3 and R4 is to limit current through the LEDs to the maximum they can handle (usually 20 milliamps). 470 ohms works well with a supply voltage of 9-12 volts.


• The duty cycle of the circuit (the percentage of the time LED 1 is on to the time it is off during each cycle) is deterimed by the ratio of R1 to R2. If the value of R1 is low in relationship to R2, the duty cycle will be near 50 percent.


• The NE555 timer chip can be damaged by reverse polarity voltage being applied to it. You can make the circuit fool proof by placing a diode in series with the supply leads.

USB Reading Lamp

USB Reading Lamp

USB reading lamp is powered using USB port. The USB port provide 5 v and 100mA which is sufficient for this circuit. Cut the one end of the USB cable and use RED(pin1) and Black(pin4) for 5v positive and negative respectively.

Parts

1. c1,c2 - 100 mF 25 v
2. Zener diode - 4.7v 400m
3. R1- 220 r
4. R2- 100 r
5. T1 - SL100
6. White LED - 5 nos.
7. USB Cable

10 Stage LED Sequencer

Circuit diagram

Components

1. IC1- CD4017


2. IC2- NE555


3. C1 - 1μ


4. C2- 0.01 μ


5. R1 - 470 Ω


6. R2 - 100 KΩ


7. R3- 100 Ω


8. LED1-10 - RED LED


9. 9volt DC power supply.

For power supply you can use 9volt battery or can design separate power supply using step down transformer and 1N4007 diodes.

Variable DC Power Supply using LM317

Variable Power Supply Using LM317

Below is the circuit for variable dc power supply

R1- 240 Ω

R2- 5K VR

R2 can be replaced by fixed value resistor for fixed power supply. Following formula can be used to calculate output voltage.

Vo=1.25(1+R2/R1)

Output voltage should be2 voltage greater than input.

Parts for current setup

 
• D1, D2 - 1N4001
• C1-0.1 μ
• C2 - 10 μ 50v
• voltage regulator - LM317
 

20 Watt Inverter

This circuit will drive a 40 watt fluorescent or two 20-watt tubes in series. The transformer is wound on a ferrite rod 10mm dia and 8cm long. The wire diameters is 0.61mm wire for the primary and 0.28mm wire for the secondary and feedback winding.

The circuit will take approx. 1.5amp on 12v, making it more efficient than running the tubes from the mains. A normal fluorescent takes 20 watts for the tube and about 15 watts for the ballast.

Note: Do not remove the tube when the circuit is operating as the spikes produced by the transformer will damage the transistor

Parts list

1. Transistor – BC338 and TIP 3055


2. Resistance – 47 K, 47 R, 180 R, 2R2


3. Variable Resistance – 100k


4. Capacitors – 100u 16v, 100n


5. On/Off Switch


6.  1 ferrite rod 10mm in 8mm long


7. 30 m winding wire .28mm dia


8. 4 m winding wire .61mm dia


9. 2* 20 watt tube or 1* 40 watt tube


10. 12 v DC power supply

Lamp Dimmer

12v LAMP Dimmer


[caption id="attachment_82" align="aligncenter" width="308"] 12v Lamp Dimmer[/caption]

Parts

1. IC 1 – NE555


2. Transistor – 2N2955 -1


3. Resistance – 1k(2 no.), 100 Ω


4. Variable Resistance – 50k


5. Capacitor – 0.1 µF


6. Diode – 1N4001 – 3


7.  12v 2 amp Bulb

Input Voltage is 12v. To create your own bench top power supply use the circuit shown in http://electronichobbyist.wordpress.com/2012/06/17/regulated-dc-power-supply-circuit/

LED Basics

Today LED has become an integral part of consumer electronics.

LED TV, LED Display, LED Lights and so on. These are becoming very popular because of there low power consumption.

What is LED?
LED stands for Light emitting diode.

A light emitting diode is essentially a PN junction semiconductor diode that emits a monochromatic(single) colour light when operated in a forward biased direction.
For detail in technical evolution refer the following url

http://en.wikipedia.org/wiki/Light-emitting_diode

Early LEDs were only bright enough to be used as indicators, or in the displays of early calculators and digital watches. More recently they have been starting to appear in higher brightness applications.

Characteristics voltage drop

When a LED is connected around the correct way in a circuit it develops a voltage across

it called the CHARACTERISTIC VOLTAGE DROP. A LED must be supplied with a voltage that is higher than its "CHARACTERISTIC VOLTAGE"  via a resistor - called a VOLTAGE DROPPING RESISTOR or CURRENT LIMITING RESISTOR

How LED works?

LED and resistor are placed in series and connected to a voltage.As the voltage rises from 0v, nothing happens until the voltage reaches about 1.7v. At this voltage a red LED just starts to glow. As the voltage increases, the voltage across the LED remains at 1.7v but the current through the LED increases and it gets brighter. As the current increases to 5mA, 10mA, 15mA, 20mA the brightness will increase and at 25mA, it will be a maximum.

This is just a simple example as each LED has a different CHARACTERISTIC VOLTAGE DROP and a different maximum current.

In the diagram below we see a LED on a 3v supply, 9v supply and 12v supply. The current-limiting resistors are different and the first circuit takes 6mA, the second takes 15mA and the third takes 31mA. But the voltage across the red LED is the same in all cases.

Head Voltage

As the supply-voltage increases, the voltage across the LED will be constant at 1.7v (for a red LED) and the excess voltage will be dropped across the resistor. The supply can be any voltage from 2v to 12 or more. The resistor will drop 0.3v to 10.3v. This is called HEAD VOLTAGE.

The voltage dropped across this resistor, combined with the current, constitutes wasted energy and should be kept to a minimum.



Most supplies are derived from batteries and the voltage will drop as the cells are used.

Here is an example of a problem:
Supply voltage: 12v
7 red LEDs in series = 11.9v
Dropper resistor = 0.1v
As soon as the supply drops to 11.8v, no LEDs will be illuminated.
Example 2:
Supply voltage 12v
5 green LEDs in series @ 2.1v = 10.5v
Dropper resistor = 1.5v
The battery voltage can drop to 10.5v
Suppose the current @ 12v = 25mA.
As the voltage drops, the current will drop.
At 11.5v, the current will be 17mA
At 11v, the current will be 9mA
At 10.5v, the current will be zero

Many batteries drop 1v and still have over 80% of their energy remaining. That's why you should design your circuit to have a large HEAD VOLTAGE.

Some Basic circuits using LED

1. Polarity Tester



2. Continuity Tester



3. USB Reading Lamp

http://electronichobbyist.wordpress.com/2012/08/04/usb-reading-lamp/

Regulated DC Power Supply Circuit

Below is the regulated DC power supply( 12, 8, 5 v) circuit. This circuit can be customized by adding 9v and 6v voltage regulator.

Also, the 4 diodes can be replaced by bridge rectifier.



If you are looking for a variable power supply then click here

Basic Power Supply Circuits - Part 2

Simplest DC power supply circuit using 78XX is shown below.



Parts

D1, D2, D3, D4 - 1N4007

IC1 - 7812

IC2 - 7805

C1 – 1000 mf

C2 – 330 mf

C3 – 10 mf

T1 - 12 v Step down transformer, 1 A.

Laptop Audio Amplifier

Laptop Audio Amplifier.