During a previous experiment, you applied dimensional analysis to determine an equation for T that governs the timing of your mystery circuit. You then performed a series of measurements to determine values for the scaling constants k1 and k2.

You also determined that the transistor Q1 controls the capacitor charging and discharging cycles. It was noted that when the transistor is 'off', the capacitor charging current is controlled by a resistance R_c made up of R4 and R5 in series, while the capacitor discharge resistance R_d is R5.

You can now verify that your equation was correct by comparing it to a theoretical expression for T obtained using measurements of the maximum and minimum voltages of the capacitor charge/discharge waveform.

To minimize the measurement error, adjust the resolution, in this case the time base and the sensitivity of the oscilloscope, to have the region of interest, in this case a single charge or discharge cycle framed by the mesurement cursors, fill most of the screen.

Accompany your scope measurements with error estimates. Use the smallest incremental change in cursor value to approximate the measurement error for a given gain/timebase setting. Save your data sets and screenshots.

Prelab preparation

To prepare for this lab session, be sure to have evaluated from your experimental data correct values for the scaling constants k1 and k2 used in the timing equation. Verify that these are correct by solving for several pairs of the T(R4,R5,C) data sets that you obtained and compare the results. As you will discover during this lab session, the theoretical analysis predicts that k1=ln(2)~0.693 and k2=2.0 if the capacitor cycles between 1/3 and 2/3 of the charging voltage. Your data should yield similar results.