# Squidwrench Electronics Workshop: Session 2

Some ex post facto notes from the second SquidWrench Electronics Workshop. This turned out much more intense than the first session, with plenty of hands-on measurement and extemporized explanations.

Measure voltage across and current through 4.7 kΩ 5 W resistor from 0.5 V to 30 V. Note importance of writing down what you intend to measure, voltage values, units. Plot data, find slope, calculate 1/slope.

Introduce parallel resistors: 1/R = 1/R1 + 1/R2. Derive by adding branch currents, compute overall resistance, factor & reciprocal.

Review metric prefixes and units!

Introduce power equation (P = E I) and variations (P = I² R, P = E²/R)

Measure voltage across  and current through incandescent bulb (6 V flashlight) at 0.1 through 6 V, note difference between voltage at power supply and voltage across bulb. Plot data, find slopes at 1 V and 5 V, calculate 1/slopes.

Measure voltage across ammeter with bulb at 6 V, compute meter internal resistance, measure meter resistance. Note on ammeter resistance trimming.

Measure voltage across and current through hulking power diode from 50 mV – 850 mV. Note large difference between power supply voltage and diode voltage above 750-ish mV. Note power supply current limit at 3 A. Plot, find slopes at 100 mV and 800 mV, calculate 1/slopes. Compare diode resistance with ammeter resistance.

Review prefixes and units!

The final whiteboard:

Hand-measured data & crude plots FTW!

## 4 thoughts on “Squidwrench Electronics Workshop: Session 2”

1. Hexley Ball says:

Outstanding job, Ed. Your audience is lucky to get such a well-considered set of exercises. I especially like the emphasis on practical points, like ammeter burden voltage.

Now that you’ve got them warmed up, how about assigning them some homework, like figuring out the resistance of the hairball resistor circuit in this classic xkcd comic: https://xkcd.com/730/

1. Ed says:

To be honest, I was making some of it up as we went along, based on questions & digressions. We had no idea who’d show up for either session, nor what they knew, so I started with the basics and rolled outward.

Insisting on actual measurements definitely helped nail down the concepts, because at the beginning nobody knows how to hook things up or where to put the meters. Next session will introduce resistors as current limiters, lighting various LED colors, and plenty of current-voltage measurement. Ought to be a hoot … [grin]