Circuits and Systems 1 Spring 2004 Lab Handout #0 This handout contains vital information about the rules and regulations that are to be followed during the lab sessions. Moreover it also gives you a brief introduction to some devices and components that will be commonly used during the lab sessions. LAB RULES 1. Labs are a compulsory component of the course and thus lab attendance is mandatory. 2. We will have 100 minutes lab session each week. 3. You are not allowed to bring any edibles to the lab. 4. All lab equipment is marked and has a number written behind it. You have to write down the equipment number of each device on a piece of paper, which is to be returned to the TA at the end of each lab session. 5. Please refrain from moving around during the lab sessions and work on your own bench. 6. You are required to return all pieces of equipment (power supplies etc.) and components (resistors etc.) are to be returned to the Lab Supervisor after the lab session. All cables must be coiled in the same manner in which they were received. 7. Get a TA to sign your data before leaving the lab. TA will sign this data after inspecting your table. Digital Multimeter A meter is a measuring instrument. An ammeter measures current, a voltmeter measures the potential difference (voltage) between two points, and an ohmmeter measures resistance. A multimeter combines these functions, and possibly some additional ones as well, into a single instrument. Before going in to detail about multimeters, it is important for you to have a clear idea of how meters are connected into circuits. Diagrams A and B below show a circuit before and after connecting an ammeter: A B Thus if we want to measure current through a component the ammeter is connected in series to it (as shown in the figure) as current remains constant in series connection. Diagram C shows the same circuit after connecting a voltmeter: A C As voltage is actually the difference of potentials across a component, voltmeter is always connected in parallel to the component across which we want to measure voltage. An ohmmeter does not function with a circuit connected to a power supply. If you want to measure the resistance of a particular component, you must take it out of the circuit altogether and test it separately, as shown in diagram D: Thus voltmeters and Ohmmeters are connected across components and an ammeter is connected in series to a component The Multimeter that you will be provided during the lab look as follows: The four circles to the left side of the meter panel are terminals in which you will insert the wires that will later be used for various measurements. The black terminal is the negative terminal and the red one is the positive terminal. Both are to be properly connected in order to obtain correct measurements. While measuring voltages remember to connect the negative terminal to the ground of source. The four buttons on the left enable you to select the appropriate option for which the meter is to be used (i.e. for measuring current etc.). The remaining buttons help the meter to define the range in which the output is expected i.e. if we want to measure a small resistance we will set the range value in Ohms rather than kilo ohm in order to get an accurate result. If the value of the component under consideration is significantly lower than the value expected set on the meter (i.e. if you have set the output value to be in kilo ohms where as the resistance is actually in milli-ohms) the meter would give a negative output. Oscilloscope An oscilloscope is a ‘voltmeter’ with a graphical display for indicating the actual waveform of the signal under observation. The oscilloscopes provided in the lab look as follows: These oscilloscopes have dual input terminals, which can be used to superimpose one input onto the other for direct comparison. However initially we shall restrict ourselves to the usage of a single input terminal. There is an internal clock generator on the oscilloscope for calibration purposes. You need not connect the ground terminal while using the internally generated signals. Connect the testing probes with the metallic hook on the bottom right corner of the oscilloscope. Use the measure button for automatically adjusting the oscilloscope for the current settings. The oscilloscope has control knobs for adjusting the vertical (voltage) and horizontal (time) scales. Signal (function) Generator The signal generator provided in the lab can generate sinusoidal, triangular and pulse waveforms of varying frequencies, amplitudes and skew rates. The push buttons are used for coarse settings of the frequency where as the control knob is used for fine settings. Power Supply It is a standard device that can be used as a dual power source. When using it as two independent sources, it can provide voltages in the range of 0-30 V and current between 0-3V. This range can be increased it we join the terminals of the supply so that it acts as a single supply. Bread Board You will use LOGIC TRAINER TD 1002 during your experiments for connecting circuit components. It contains a breadboard like the one shown below: All our circuits will be made on the breadboard. Each independent column (i.e. like the one boxed in the diagram) is connected. The Logic Trainers provided to you in the lab also provide you with four output voltages that are –5V, +5V, -12V, +12V. Resistors Resistor is a component that will be frequently used during the lab experiments. The resistors that will be used during experiments follow a specific convention, which is used to know the resistance of the component. It contains different colored bands and each band signifies specific information. Each resistor is color coded as follows: Color Value Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Gray 8 White 9 First find the tolerance band, it will typically be gold ( 5%) and sometimes silver (10%). Starting from the other end, identify the first band - write down the number associated with that color; in this case Blue is 6. Now 'read' the next color, here it is red so write down a '2' next to the six. (you should have '62' so far.) Now read the third or 'multiplier' band and write down that number of zeros. In this example it is two so we get '6200' or '6,200' or 6.2 kΏ. If the 'multiplier' band is Black (for zero) don't write any zeros down. If the 'multiplier' band is Gold move the decimal point one to the left. If the 'multiplier' band is Silver move the decimal point two places to the left. If the resistor has one more band past the tolerance band it is a quality band. Read the number as the '% Failure rate per 1000 hour'. This is rated assuming full wattage being applied to the resistors. (To get lower failure rates, resistors are typically specified to have twice the needed wattage dissipation that the circuit produces) 1% resistors have three bands to read digits to the left of the multiplier. They have a different temperature coefficient in order to provide the 1% tolerance.