10. Things to Try Before Moving On

These exercises will solidify the chapter immeasurably more than re-reading.

1. Plot a real diode's V-I curve. Use a 1N4148, a 1 kΩ resistor, a 0–10 V variable supply, and a multimeter. Sweep the voltage in 0.1 V steps from 0 to 1 V; for each, measure the current. Plot it. The exponential is real.
2. Build a half-wave rectifier with a 6.3 V transformer (or function generator at 10 kHz, 5 V peak). Watch the output on a scope, with and without a 100 µF filter cap. Notice the ripple, measure its frequency, compare to your calculation.
3. Build a CE amplifier using a 2N3904 and the self-bias topology. Pick $R_1 = 47$ kΩ, $R_2 = 10$ kΩ, $R_C = 4.7$ kΩ, $R_E = 1$ kΩ, $V_{CC} = 12$ V. Measure the DC bias point. Then inject a small AC signal (10 mV peak, 1 kHz) at the input through a coupling cap. Measure the output. Compare gain to your prediction.
4. Test thermal stability. Take the same CE amplifier. Touch the 2N3904 with your finger, watch the bias drift on a meter. Now warm it more (a soldering iron held near — not on — the part, briefly). Watch the bias. The drift is real and obvious without expensive equipment.
5. Build a MOSFET switch. Use a 2N7000 to drive an LED from a microcontroller pin. Notice that the gate draws essentially no current — the MCU pin barely cares.

When the above feel intuitive — when you can predict roughly what a circuit will do before you build it — you have the chapter under your belt.