Variable Resistors in a Circuit
Variable Resistors in a Circuit
Embedded Files
Exercise Five: The Potentiometer
Exercise Five: The Potentiometer
Background Knowledge:
Background Knowledge:
How to draw a Schematic
Resistors, Variable Resistors, and LEDs
How to read and use a Multimeter
What you'll need:
What you'll need:
1 - 9 Volt Battery
1 - 9 Volt Battery Harness
1 - Breadboard
1 - 1N4007 Rectifier Diode
1 - 470-Ohm 1/4 Watt THR
1 - 100 K-Ohm Potentiometer
1 - Red 5mm LED
Not all resistors are fixed like the color-banded ones we’ve been working with. A common variable resistor is called a potentiometer. They are often nicknamed “pots.” They are commonly found in analog volume controls.
There is a drawing of a potentiometer without a cover. A potentiometer works because the rotating wiper slides across a carbon track and connects that to the center. The leg on the left is referred to as A, the center as C (center), and the right as B.
The distance between A and B always stays the same, so the resistance between A and B is always the same. The value for the potentiometer to the left is 100,000 ohms. This means the value of resistance between A and B is always 100 Kilo-ohms. Ideally, this means the minimum resistance C would have is zero ohms, and the maximum is 100 Kilo-ohms.
The carbon in the ring is similar to the carbon graphite in a pencil. Pencil lead is a combination of carbon and clay. Carbon is the conductor. Clay is the insulator
Steps
Steps
Draw the schematic diagram and label the components.
When labeling your components in a circuit each resistor will be R#, so in this circuit R1, R2, R3, and R4. R1 will typically be the resistor closest to the positive node.
Your circuit should also have the nominal values of each component annotated on the schematic diagram. With Resistors, you can find this using the Resistor Color Codes.
Using what we know about current, you should also label the schematic with the anticipated current flow direction.
Grab a 100 Kilo-ohm potentiometer. Use your multimeter to measure the actions listed below.
Set the dial to zero and measure the resistance between legs A and B.
Adjust the dial and measure the resistance between legs A and B.
Did you notice and change? Why?
Adjust the dial about halfway.
Measure the resistance between the left leg (A) and the center leg (C.)
Turn the dial to any position.
Measure the resistance between the left leg (A) and the center leg (C.)
5. Build the circuit to the left.
This circuit includes a 9V power source, the safety diode, a resistor, a potentiometer, and an LED. Make sure the power source is set to 9VDC and measure with your multimeter. When you build this circuit and interact with it, you should do and ask the following:
6. Set the Potentiometer dial somewhere approximately in the middle and leave it there to complete the following chart.
Remember, power cannot be flowing to the circuit when measuring resistance. Do not fill in the shaded cells.
Questions:
Questions:
What is the purpose of a variable resistor?
Why is the potentiometer not grounded on terminal B? When would it have to be?
As you turn the dial of the potentiometer, the LED should brighten and dim. What is happening here?
Why is there a 470-ohm fixed resistor in this circuit?
Exercise Six: Light-Dependent Resistors
Exercise Six: Light-Dependent Resistors
Background Knowledge:
Background Knowledge:
How to draw a Schematic
Resistors, Variable Resistors, and LEDs
How to read and use a Multimeter
Current Flow and Voltage Drops in a Series Circuit
What you'll need:
What you'll need:
1 - 9 Volt Battery
1 - 9 Volt Battery Harness
1 - Breadboard
1 - 1N4007 Rectifier Diode
1 - 1 M-Ohm LDR (Dark)
1 - Red 5mm LED
Another variable resistor is the LDR, the light-dependent resistor, sometimes called Photoresistors. LDRs are electronic components that change their resistance in response to changes in the intensity of light falling on their surface. The symbol for the LDR can be found on our Schematics Page.
There is no room to place a value on a physical LDR. They are ordered and made to a specific value and when you order them will be placed in a bag and labeled. If you find an LDR loose or out of its bag, an easy way to find its maximum resistance value is to measure is to measure it in absolute darkness. To make this easy, insert the LDR in the breadboard with its legs separated to support itself, place a pen cap over the sensor, and measure it with a multimeter. Because LDRs can be well into the millions of Ohm's set your multimeter to the highest resistance value and work down.
Steps
Steps
Draw the schematic diagram and label the components.
When labeling your components in a circuit each resistor will be R#, so in this circuit R1, R2, R3, and R4. R1 will typically be the resistor closest to the positive node.
Your circuit should also have the nominal values of each component annotated on the schematic diagram. With Resistors, you can find this using the Resistor Color Codes.
Using what we know about current, you should also label the schematic with the anticipated current flow direction.
2. Connect a 9V battery to the circuit.
With the lights on, the current should be flowing now and the LED should be on. Note the brightness of the LED- it should be fairly bright.
Place the lid of a sharpie pen over the LDR. The LED should be dim to nothing.
3. Disconnect the battery.
Measure and record the resistance of the LDR in the light. It may be necessary to take a rough average because it will be jumping around wildly because of the multimeters sensitivity.
Place a dark black pen lid over the LED (or set the LDR to dark on TinkerCAD) and measure the resistance again.
4. Consider the “waterfall” diagrams presented below. From brightest to darkest conditions, what would be the best order of these diagrams regarding the LDR’s effect on the brightness of the LED.
#1 _______________ #2 _______________ #3 _______________ #4 _______________
5. Finally, summarize your results in this chart.
The Voltage Drop and Current can be measured using the multimeter while power is on.
Resistance must be measured while the voltage source is unplugged.
Questions:
Questions:
What is the difference between a LDR in the dark and in the light?
Why would being able to receive input from the surrounding area be important to electronics?
What is the relationship between the amount of light on the LDR and the LDR’s resistance?
Note the minimum resistance that occurs on the LDR in the light. Why is the 470-ohm resistor not used in this circuit?
Google Sites
Report abuse