OTHER ELECTRONIC CIRCUIT

Student DC Power Supply

noreply@blogger.com (Go2Media) — Tue, 16 Dec 2008 02:52:00 +0000

Here's a simple DC power supply having three output terminals: regulated +5VDC, unregulated +10VDC and 7.5VAC. The supply is suitable for microcontroller experimenting for any student.

My workbench has many broken devices and most of them will be used as the part for making the electronic projects. One day I looked at the broken radio, I found there's an AC line cord with socket and a transformer. Actually I like the way they used AC socket with the AC cord. I thought why don't make a simple DC supply from these parts. Most of the DC adapters provide only DC output. But not AC output, some of the uC circuit need a +5V for digital circuit, some need an AC line voltage for timing synchronization, digitizing sine wave, and some need unregulated for relay driving. So I designed above circuit for lab usage.

The DC power supply circuit is a linear regulator providing galvanic isolation from main line through the use of isolation transformer. Quite safe for experimenting with AC voltage. Below pictures show the example of input/output terminal connections, labeling and components placement in the box. The circuit can be built using universal PCB. The output terminal is for big load connection so this makes it quite strong and good electrical contact to the load being used.

Simple DC Power Supply for Students

RF Oscilator Basic

noreply@blogger.com (Go2Media) — Fri, 31 Oct 2008 16:09:00 +0000

This basic oscillator circuit is easy to build and the components are not critical. Most of them can be found in your junk parts box. The L1 antenna coil can be made by close winding 8-10 turns of 22 gauge insulated hookup wire around 1/4" form such as pencil.

You can experiment with the size of the coil and the number of turns to see how it affects frequency and signal output of the oscillator. And the next stage is to try changing the transistor type.

You should be able to pick up its signal with a standard fm radio receiver. The "signal in" should be coupled with a disc capacitor of about 0.1 uf to the stage in front of it.

More of Basic RF Oscilator

Resistor Calculator for LEDs (serial and parallel) V.2

noreply@blogger.com (Go2Media) — Thu, 09 Oct 2008 03:40:00 +0000

Software that calculates the resistor value and its power consumption in different LED's circuit configurations (simple, series o parallel) according to the source voltage, the LED's voltage and the wanted current value. All are shown in the same screen in order to make direct comparisons on values.

Download : Resistor Calculator v.2 (67 Kb/ZIP)

Electronic Book Tutorial for Hobbyists

noreply@blogger.com (Go2Media) — Thu, 10 Jul 2008 17:39:00 +0000

Best series of books to improve basics in Electronics. Use the software for previewing the files according the topic. Here's the download links:

Unzip the Material and the Software

Material(Materials.zip)
- Direct Current
- Alternate Current
- Active Devices
- Electronic Circuits
- Digital Electronics
- Digital Computers
- Survey of Electronic Hobbies
Software(WinDjView-05.zip)

Electronics Manual Handbook

noreply@blogger.com (Go2Media) — Sat, 28 Jun 2008 15:18:00 +0000

An introduction to electronics covering Resistors, Capacitors, Transistors, Digital Logic and simple Projects. Ideal for school use.

Download English Version
Download Spanish Version Part1

Source : Jim Fuller

Finding the Value of a Resistor by Color Codes

noreply@blogger.com (Go2Media) — Thu, 26 Jun 2008 05:14:00 +0000

To calculate the value of a resistor using the color coded stripes on the resistor, use the following procedure.

Step One: Turn the resistor so that the gold or silver stripe is at the right end of the resistor.

Step Two: Look at the color of the first two stripes on the left end. These correspond to the first two digits of the resistor value. Use the table given below to determine the first two digits.

Step Three: Look at the third stripe from the left. This corresponds to a multiplication value. Find the value using the table below.

Step Four: Multiply the two digit number from step two by the number from step three. This is the value of the resistor n ohms. The fourth stripe indicates the accuracy of the resistor. A gold stripe means the value of the resistor may vary by 5% from the value given by the stripes.

Resistor Color Codes (with gold or silver strip on right end)

Follow the above procedure with the examples below and soon you will be able to quickly determine the value of a resistor by just a glance at the color coded stripes.

Examples

Example1:
You are given a resistor whose stripes are colored from left to right as brown, black, orange, gold. Find the resistance value.

Step One: The gold stripe is on the right so go to Step Two.

Step Two: The first stripe is brown which has a value of 1. The second stripe is black which has a value of 0. Therefore the first two digits of the resistance value are 10.

Step Three: The third stripe is orange which means x 1,000.

Step Four: The value of the resistance is found as 10 x 1000 = 10,000 ohms (10 kilohms = 10 kohms).

The gold stripe means the actual value of the resistor mar vary by 5% meaning the actual value will be somewhere between 9,500 ohms and 10,500 ohms. (Since 5% of 10,000 = 0.05 x 10,000 = 500)

Example2:
You are given a resistor whose stripes are colored from left to right as orange, orange, brown, silver. Find the resistance value.

Step One: The silver stripe is on the right so go to Step Two.

Step Two: The first stripe is orange which has a value of 3. The second stripe is orange which has a value of 3. Therefore the first two digits of the resistance value are 33.

Step Three: The third stripe is brown which means x 10.

Step Four: The value of the resistance is found as 33 x 10 = 330 ohms.

The silver stripe means the actual value of the resistor mar vary by 10% meaning the actual value will be between 297 ohms and 363 ohms. (Since 10% of 330 = 0.10 x 330 = 33)

Example3:
You are given a resistor whose stripes are colored from left to right as blue, gray, red, gold. Find the resistance value.

Step One: The gold stripe is on the right so go to Step Two.

Step Two: The first stripe is blue which has a value of 6. The second stripe is gray which has a value of 8. Therefore the first two digits of the resistance value are 68.

Step Three: The third stripe is red which means x 100.

Step Four: The value of the resistance is found as 68 x 100 = 6800 ohms (6.8 kilohms = 6.8 kohms).

The gold stripe means the actual value of the resistor mar vary by 5% meaning the actual value will be somewhere between 6,460 ohms and 7,140 ohms. (Since 5% of 6,800 = 0.05 x 6,800 = 340)

Example 4:
You are given a resistor whose stripes are colored from left to right as green, brown, black, gold. Find the resistance value.

Step One: The gold stripe is on the right so go to Step Two.

Step Two: The first stripe is green which has a value of 5. The second stripe is brown which has a value of 1. Therefore the first two digits of the resistance value are 51.

Step Three: The third stripe is black which means x 1.

Step Four: The value of the resistance is found as 51 x 1 = 51 ohms.

The gold stripe means the actual value of the resistor mar vary by 5% meaning the actual value will be somewhere between 48.45 ohms and 53.55 ohms. (Since 5% of 51 = 0.05 x 51 = 2.55)

Other Resistor Information

There are some more rules that may be useful when working with resistors. You do not need to know them but if you need a resistor with a value that you do not have, you my be able to use the following information to create the value of resistor you need.

First Rule for Resistors : Series Connection

When two resistors are connected in series, as shown in Figure 1, the new resistance between points A and B is R1 + R2.

Figure 1

The resistors add together. For example if R1 = 500 ohms and R2 = 250 ohms then the resistance between points A and B would be R1 + R2 = 500 + 250 = 750 ohms.

Second Rule for Resistors : Parallel Connection

When two resistors are connected in parallel, as shown in Figure 2, the new resistance is smaller than either R1 or R2. The new resistance between points A and B is (R1 x R2) / (R1 + R2).

Figure 2

For example, if R1 = 500 and R2 = 250 then the resistance between points A and B = (500 x 250) / (500 + 250) = (125,000) / (750) = 167 ohms. If R1 = R2 then the new resistance is just R1 / 2.

Using these two rules, resistors can be combined to form new resistance values.

Finding Voltage and Current Using Ohm's Law

noreply@blogger.com (Go2Media) — Thu, 26 Jun 2008 04:40:00 +0000

There is a simple relationship between current, voltage and resistance. This relationship is called Ohm’s Law. The formula is the following.

Difference in Voltage = Current * Resistance

or DV = I * R

This is Form 1 of Ohm's Law.

To find current and resistance the following forms can be used. They are the same as the above formula but in a different form.

Form 2: Current = Difference in Voltage / Resistance

or I = DV / R

Form 3: Resistance = Difference in Voltage / Current

or R = DV / I

These formulas are always used for situations where there are two points with a resistor between them. DV is the difference in voltage between the two points and current is what flows between the two points. These simple relationships allow us to calculate many things. Given any two of the three values (Current, Resistance, and Difference in Voltage) the third can be found. The most common calculation is for current. Voltage is easy to measure and the resistance can be found from the resistor (see color codes). Once these values are known, current can be calculated using Form 2 of Ohm’s law, I = DV / R. For example, consider the problem shown in Figure 1. One side is at 0 volts (ground) and the other side is at 5 volts (with a multimeter, black probe on right side, red probe on left side).

Figure 1

The voltage difference between Point A and Point B is 5 - 0 = 5 volts (DV=5). There is a resistor between the two points which has a value of 500 ohms (R=500). We know that current flows from a point of high voltage to a point of low voltage so we can draw an arrow from the higher voltage to the lower voltage.

Figure 2

Now we can find the current flowing through the resistor using Form 2 of Ohm's Law.

I = DV / R

DV / R = 5 / 500

5 / 500 = 0.01 Amps

0.01 Amps = 10 milliAmps

10 milliamps can be abbreviated as 10 mA

This means the current is 10 mA. ( I = 10mA )

Now to check our answer we can use Form 1 and Form 3 of Ohm’s law. We have to use the value of current in Amps for these formulas. So if we have I = 0.01 Amps and Resistance = 500 ohms then by using Form 1 of Ohm’s law we can find:

Difference in Voltage = DV

DV = I * R

I * R = 0.01 * 500

0.01 * 500 = 5 volts

This is the voltage we started with so the value we found for the current must be right.

We can also check the answer with Form 3 by using I = 0.01 Amps and DV = 5 volts.

Resistance = R

R = DV / I

DV / I = 5 / 0.01

5 / 0.01 = 500 ohms.

So R = 500 ohms

Now consider the problem shown in Figure 3. The voltage on one side is 10 volts and the voltage on the other side is 3 volts. Therefore the voltage difference between the two points is 10 - 3 = 7 volts (DV = 7 V). The resistor is 400 ohms (R = 400).

Figure 3

Then the current flowing from left to right is

I = DV / R

DV / R = 7 / 400

7 / 400 = 0.0175 Amps

0.0175 Amps = 17.5 milliAmps

17.5 milliAmps = 17.5 mA

This means the current flowing from the left to the right is 17.5 mA.

Now suppose we have two points with a voltage difference of 5 volts. Point A is at 5 volts and Point B is at 0 volts (ground). (Notice that the voltage difference is the important part. If Point A is at 7 volts and Point B is at 2 volts then the voltage difference is the same, 7 - 2 = 5 volts.) Now suppose we want a current to flow between Points A and B and we want the current to be 0.02 Amps ( I = 0.02 Amps = 20 mA).

Now we need to find the value of the resistor so we use Form 3 of Ohm’s Law.

Resistance = Difference in Voltage / Current or R = DV / I

DV / I = 5 / 0.02 = 250 ohms

This means that putting a resistor with a value of 250 ohms between Points A and B will make a current flow from Point A to Point B and the current will be 0.02 Amps (20 mA). Now using the values of voltage and resistance, check the value of the current using Form 2 of Ohm’s law.

Basic Electrical Components

noreply@blogger.com (Go2Media) — Thu, 26 Jun 2008 04:35:00 +0000

Resistors
Resistors are components that have a predetermined resistance. Resistance determines how much current will flow through a component. Resistors are used to control voltages and currents. A very high resistance allows very little current to flow. Air has very high resistance. Current almost never flows through air. (Sparks and lightning are brief displays of current flow through air. The light is created as the current burns parts of the air.)

A low resistance allows a large amount of current to flow. Metals have very low resistance. That is why wires are made of metal. They allow current to flow from one point to another point without any resistance. Wires are usually covered with rubber or plastic. This keeps the wires from coming in contact with other wires and creating short circuits. High voltage power lines are covered with thick layers of plastic to make them safe, but they become very dangerous when the line breaks and the wire is exposed and is no longer separated from other things by insulation.

Resistance is given in units of ohms. (Ohms are named after Mho Ohms who played with electricity as a young boy in Germany.) Common resistor values are from 100 ohms to 100,000 ohms. Each resistor is marked with colored stripes to indicate it’s resistance. To learn how to calculate the value of a resistor by looking at the stripes on the resistor, go to Resistor Values which includes more information about resistors.

Variable Resistors
Variable resistors are also common components. They have a dial or a knob that allows you to change the resistance. This is very useful for many situations. Volume controls are variable resistors. When you change the volume you are changing the resistance which changes the current. Making the resistance higher will let less current flow so the volume goes down. Making the resistance lower will let more current flow so the volume goes up. The value of a variable resistor is given as it’s highest resistance value. For example, a 500 ohm variable resistor can have a resistance of anywhere between 0 ohms and 500 ohms. A variable resistor may also be called a potentiometer (pot for short).

Diodes
Diodes are components that allow current to flow in only one direction. They have a positive side (leg) and a negative side. When the voltage on the positive leg is higher than on the negative leg then current flows through the diode (the resistance is very low). When the voltage is lower on the positive leg than on the negative leg then the current does not flow (the resistance is very high). The negative leg of a diode is the one with the line closest to it. It is called the cathode. The postive end is called the anode.

Usually when current is flowing through a diode, the voltage on the positive leg is 0.65 volts higher than on the negative leg.

LED
Light Emitting Diodes are great for projects because they provide visual entertainment. LEDs use a special material which emits light when current flows through it. Unlike light bulbs, LEDs never burn out unless their current limit is passed. A current of 0.02 Amps (20 mA) to 0.04 Amps (40 mA) is a good range for LEDs. They have a positive leg and a negative leg just like regular diodes. To find the positive side of an LED, look for a line in the metal inside the LED. It may be difficult to see the line. This line is closest to the positive side of the LED. Another way of finding the positive side is to find a flat spot on the edge of the LED. This flat spot is on the negative side.

When current is flowing through an LED the voltage on the positive leg is about 1.4 volts higher than the voltage on the negative side. Remember that there is no resistance to limit the current so a resistor must be used in series with the LED to avoid destroying it.

Switches
Switches are devices that create a short circuit or an open circuit depending on the position of the switch. For a light switch, ON means short circuit (current flows through the switch, lights light up and people dance.) When the switch is OFF, that means there is an open circuit (no current flows, lights go out and people settle down. This effect on people is used by some teachers to gain control of loud classes.)

When the switch is ON it looks and acts like a wire. When the switch is OFF there is no connection.

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