3.2 Bipolar transistors

I declare: solidlikelyshaky

1. Explain base, collector, emitter, gain, and identify NPN and PNP with the multimeter.
2. Build a transistor switch to drive a relay or a power LED from a 3.3 V output, and calculate the base resistor.
3. Explain saturation and why you saturate a switching transistor.
4. Build a common-emitter amplifier, measure its gain and say what sets it.
5. Explain the Darlington and the complementary push-pull stage, and where you meet them (relay driver, audio output).
6. Explain the optocoupler and use it to isolate a 3.3 V control from a circuit on another ground.
7. Diagnosis: a transistor that heats up while switching, not saturated enough, load too heavy or base underdriven; the measurements that decide.