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Instructions for lab 4, which focuses on using a digital multimeter (dmm) to measure voltage, current, and resistance. The lab covers the components of a dmm, including leads, function selector, readout, and fuse. It also explains how the dmm works and discusses other functions such as transistor testing, capacitance meter, diode tester, battery tester, and frequency counter. Instructions for two experiments: measuring resistor tolerances and dmm accuracy, and measuring led current and output intensity.
Typology: Lab Reports
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Potentiometers are resistors whose value can be varied, depending on the position of a shaft or screw. The picture below shows some examples of different styles.
Potentiometers. Circular ones work like the diagram on the left. The center terminal is connected to the “wiper”, which conducts a piece of carbon, plastic or coil of wire. The rectangular “pot” is constructed as shown on the right, with a tiny lead screw for adjustment.
DMM, five x 1kΩ resistors.
Procedure:
er 2 measure the resistance of each resistor and record measures each resistor three times. ultimeters with one of the other groups at your bench and repeat, noting the new DMM in Compare the results by analyzing the differences between the measurements to see tor, and the tolerance of the
ttention to the analysis section.
DMM, LED, 4 x 1kΩ resistor, breadboard, power supply, wires
Procedure:
the power supply and switch the DMM to measure DC Volts. Measure the voltage across e h
the brightness of the LED. Compute the equivalent resistance of the two parallel
so that each person
your records. if you can detect the influence of the DMM, the influence of the opera resistors.
Wri et up: Write up this experiment as instructed in the Labs handout. Pay special a
Equipment:
case. The Anode is usually the longer of the two leads, and the
resistance of the resistor you use, or use one with known resistance the value.
Equipment Breadboard, photoresistor, DMM, assorted fixed resistors, potentiometer, 5V power supply, wires.
Procedure
Design a circuit that uses a 5V power supply, one or more fixed resistors and a photoresistor (PR) to make a day/night detector. Depending on the range of your photoresistor you may or may not have the fixed resistors you need in your lab kit to construct your design. That’s OK, create the design and we’ll find you the resistors you need. Your circuit should be set up so that if it is “daylight” the voltage at the output of the circuit is less than 2 Volts, and if it is “night” the voltage is greater than 3.5 volts. To do this, you should have a photoresistor in which the ratio of Rdark to Rlight is at least 4:1, preferably more. If your PR is not that sensitive, try shining a flashlight onto it during the “daylight” phase and re‐measure its resistance to see if you get a 4:1 or better ratio. If not, speak to a T/A about getting a different PR.
Document your design , including your calculations to choose a fixed resistor value, and build your circuit. Show the T/A your calculations and demonstrate your circuit to a T/A by showing the output on your DMM for the dark and daylight situations.
Equipment Potentiometer, DMM, 5V power supply, wires.
Procedure Connect the power supply to your potentiometer as shown in the diagram at right.
Now change the position of the shaft and read again. Predict the voltage you will read at the wiper when you reconnect the power supply. Try it and verify your prediction.
Writeup No writeup for this experiment.
