You will need

- The execution of these works will require a basic knowledge of radio engineering,the techniques of measuring instrument (tester, ohmmeter), as well as skill with a screwdriver, soldering iron, pliers.

Instruction

1

Determine with technical documentation or schematics, what is the function of variable

**resistor**in the device (adjustable resistance or potentiometer). Install using the specification or calculation method of the nominal value/value of the variable resistance and type. Then select the proper type and the value of variable**resistor**or its equivalent.2

Test it using the meter measuring resistance (ohmmeter) find the output, which changes the resistance. It is called "slider".

3

Produce switching of the contacts, a variable

**resistor**but in accordance with her function: connect the contact of the slider**a resistor**and one of the two remaining findings to obtain the variable**resistor**and or use all the conclusions of the**resistor**and to use it as a potentiometer.4

Install the device in the device or on mounting plate and connect it conclusions in accordance with the concept. Check that the values of the fuse links (fuses), and enable compliance with safety standards the device to check its efficiency.

Useful advice

Variable resistors are used in devices where it is necessary to vary the value of resistance. With the change in resistance in the circuit will vary the current in accordance with Ohm's law. And the output of the potentiometer, we can obtain any value of voltage, but it will be always not more than the input voltage. Potentiometers are used to adjust device parameters such as output voltage, power, volume, etc.

# Advice 2 : How to calculate resistance for LEDs

Today, LEDs are used everywhere: in the quality indicators, elements of lighting, pocket torches and even traffic lights. There are thousands of models of these devices. On their basis in the home is easy to build and entertaining device. LEDs are sold in shops of radio components. Unlike incandescent lights, they cannot be connected directly to the power supply - the LEDs fail. Need a current limiting resistor. Therefore, the question of how to calculate

**resistance**for**led**stands up immediately before using it.You will need

- Reference light-emitting semiconductor devices, knowledge of standard values for resistors (series E6, E12, E24, E48), or Internet access to obtain the necessary data. A piece of paper with a pen or calculator.

Instruction

1

Find out the electrical parameters of the used led. To calculate the resistance of a resistor, it is necessary to know the forward voltage and the rated current of the device. Knowing the model, in the Handbook or on the web, find the required parameters. Make a note of them.

2

Determine the supply voltage from which is powered the led. If the power source assumes the use of the galvanic cells or accumulators, find out their rated voltage. If the led must be powered by circuits with large voltage tolerance (for example, electricity car), determine the maximum circuit voltage.

3

Calculate

**resistance**for**led**. Perform calculation according to the formula R = (Vs - Vd) / I, where Vs is the supply voltage, Vd is the forward voltage of the led and I is the rated current. Pick the nearest value larger than the resistance in one nominal series resistance. It makes sense to use a number E12. The tolerance in the nominal values for resistors, this number is 10%. So, if the calculated value of the resistance R = 1011 Ω, as a real resistance must be set to 1200 Ohms.4

Calculate the minimum required capacity of the quenching resistor. Calculate the value according to the formula P = (Vs - Vd)2 / R. the values of the variables Vs and Vd the corresponding values of the previous step. The R value is a

**resistance**calculated earlier.Note

Do not turn on the LEDs in parallel using a single damping resistor. Due to the natural variation of parameters of the devices, some of them will have an increased load, which can cause of their failure.

Useful advice

If the model of led is not known, it is possible to use a resistor with variable resistance for experimental determination of the required value.

# Advice 3 : How to choose a resistor for the led

Led is a semiconductor device that has firmly entered into our life and slowly began to replace the traditional light bulbs. He has low power consumption and small size, which positively affects the fields of its application.

Instruction

1

Remember that any led that is included in the network must be connected in series resistor required to limit current flowing through the semiconductor device. Otherwise, the probability is that the LEDs may quickly fail.

2

Therefore, before assembling the circuit containing the LEDs, carefully calculate the resistance value, which is determined as the difference between the supply voltage and direct voltage, which is calculated for a particular type of diode. It ranges from 2 to 4 Volts. The difference divide by the current of the device and eventually get the desired amount.

3

Remember, if the resistance value of the resistor accurately select fails, you better take a resistor with a slightly higher value than the desired value. The difference you'll hardly notice, because the brightness of the emitted light will decrease by a small part. Also the amount of resistance can be calculated using Ohm's law, in which the voltage flowing through the diode, is divided by the current.

4

When connecting several LEDs in series, it is also necessary to set the resistance that is calculated in the same way. Remember that there is the total voltage of all the diodes, which is taken into account in the formula for determining the parameters of the resistor.

5

Also, do not forget to connect the LEDs in parallel through a single resistor is prohibited. This is due to the fact that all devices have different dispersion parameters and some of the diodes will glow brighter, therefore it will carry a large amount of current. In the end it will lead to the fact that it will fail. Therefore, when parallel connection of the resistance set for each led separately.

# Advice 4 : How to connect the resistor

There are different wiring diagrams depending on which variable resistor can be as a source of variable resistance and potentiometer. All depends on the type of connection of the third output.

Instruction

1

Examine carefully the scheme or documentation to determine how to connect

**the resistor**in this particular case. As mentioned earlier, it can perform two functions: a source of variable resistance and the potentiometer. The documentation should be provided a variable resistance in the connection. It is best to determine the number of thumb, using a special measuring device. So you will be able to more accurately pick up a variable**resistor**or some equivalent.2

Take an ohmmeter to measure total resistance in the circuit. Connect the terminal on the closing contacts. The resistance value should be reflected on the screen. Then measure the resistance at a particular node schema. If no value is reflected, then a connection somewhere is broken.

3

Carefully inspect all contacts. If needed, connect them to any metallic wire. More reliable connection you provide when you soldering

**the resistor**. Depending on the received values, choose a suitable**resistor**. Proceed to its installation in the scheme.4

Wipaire old broken-down

**resistor**. Try to make the solder residue does not fall to the circuit to avoid circuit of neighboring contacts. Then take a new**resistor of**variable resistance. Solder it just like you just extracted.5

Follow the same precautions to prevent the formation of bridges between contacts. Turn on the circuit, check its efficiency. If it does not work or works incorrectly, peredayte

**resistor**. Some**resistor**Ah foreign-made contacts can be a little different. Swap the center pin with either of the extreme. If it did not bring the expected results, check the device for faulty new**resistor**.