EAS 327

LABORATORY 1, BASIC ELECTRONICS

AIM: The first two labs are designed to reinforce your knowledge of basic electronic test equipment (power supplies, voltmeters, chart recorders, analog and digital oscilloscopes), of simple resistor networks, and of the lowpass RC filter. Please complete the following experiments (in any order). Note: you will be provided help and supervision in these tasks, which may be a very unfamiliar!

Function of oscilloscope and signal generator: Connect a signal generator to Channel 1 of an oscilloscope. Set the triggering (timebase or sweep) to "Normal" trigger (ie. triggering by the input signal, as opposed to "automatic") on channel 1. Experiment with the two alternatives "ac coupling" and "dc coupling" (this is more interesting if you temporarily set the signal generator to give a square wave instead of a sine wave). With the setting "dc coupling," adjust the zero-level of the oscilloscope trace. Return to "ac coupling". Measure the amplitude (A, [volts]) and period (T, [sec]) of the wave from the signal generator. Deduce the frequency of the wave frequency (f = 1/T, [Hz]).
Determination of source resistance: Connect (either) signal generator to (either) oscilloscope, and adjust the signal to obtain a sine wave with a convenient amplitude A_s, and a frequency of about f=3KHz. Now add a large load resistor R_L (say, 10K ) across the output from the source. Observe the reduced amplitude A on the scope (if R_L is large, you will find A ~ A_s). Work down to a sufficiently low value of the load resistance R_L that the voltage change (A_s-A) is at least 1 V. Calculate the internal resistance R_s of the source, using the formula for a voltage divider
A/A_s = R_L/(R_L + R_s)
Function of half-bridge (i) sinusoidal input: You are provided with a protoboard, and resistors. Place the resistors R₁, R₂ in the protoboard in the configuration of a half-bridge, and connect your signal generator across the bridge as source (we may regard the input amplitude A_s as the source voltage V_s). Measure the output signal (V_o, ie. the amplitude A at the midpoint between the two resistors) on channel 2 of your scope. Compare A/A_s with the theoretical value of the output-voltage/input-voltage ratio (V_o/V_s) for a half-bridge. Repeat for several frequencies and several choices of R₁, R₂.
Function of half-bridge (ii) steady state input: Now connect a dc source to your half bridge as source. Measure the source and output signals (V_s,V_o) using a multimeter (dc voltage setting). Again compare your observations with the theoretical V_o/V_s.
Calibration of datalogger: Connect the "Analogic" voltage calibrator to the Campbell Scientific CR21X data logger (single-ended input 1). Program the logger to perform a single-ended voltage measurement on input channel 1, assuming a full scale range of +/- 5 volts. Set the sampling interval Dt=1 sec. Step the voltage calibrator across the range -5 to 5 volts, in intervals of 1 volt. Note the logger output (a number, N) corresponding to the input voltage (V). Plot a graph of N versus V.
Step response of lowpass RC filter: Build an RC lowpass filter on the prototyping board, using whichever values for R, C you wish (but bear in mind you want t = RC to be of the order of seconds, so as to resolve the response on the chart recorder). Switch on a known voltage at the filter input, using a dc power supply. From the observed step response on your chart, calculate the "time constant" t of the filter. Compare with the RC product.
Sinusoidal response of RC filter: Drive the input of your RC filter with (either) function generator, and view the output with an oscilloscope. Sweep up in frequency from very low values to very high values, and describe the input-output relationship you observe (in terms of the imput amplitude A_s and output amplitude A_o). Plot the "power gain ratio"
G=A_o²/A_s²
versus frequency f. Identify your experimental value of the "half-power frequency," f_o^exp (defined as the frequency at which G=1/2).

REPORT

Write whatever you feel is necessary to show you understood the procedures and the concepts examined here. Do so as effectively as you can: be brief, logical, creative; certainly provide complete, well-labelled circuit diagrams, noting whether the equipment was "floating" or "grounded."

Operations/skills you should have mastered...

constant attention to polarity. Tidy wiring, joints.
"zeroing" and setting the "span" or "full scale range" of a recorder ("y axis")
setting the time resolution (time base) of a recorder
judging/testing if a device/circuit floats, or is grounded
drawing circuit diagrams

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EAS 327

LABORATORY 1, BASIC ELECTRONICS

Last Modified: 24 Jan. 2005