Electronics · Reference card · Keep me all year · build 2026.09.23-1644

The Debugging Loop

Stop. Look. Touch nothing. Random wiggling destroys the evidence. Thirty seconds of looking beats ten minutes of jiggling.
Check the power. Is the power supply on? Switched to 5 V? Charged? The most embarrassing bug in all of engineering is also the most common one.
Trace the loop. Put a finger on the red wire and walk the whole path around to the black wire. If the circuit branches, trace every path. No complete loop, no flow — and the place your finger gets stuck is where the bug lives.
Interrogate every node. Say each node's letter out loud and check it against the schematic: the right legs joined? Every leg deep in the row you meant? Anything touching that shouldn't be? (A node is a row — or a pinch.)
Check the one-way parts. LED: long leg toward the + side. Later in the course: transistors and chips have directions too.
Change ONE thing. Retest. If you change three things and it works, you learned nothing — and maybe planted two new bugs. One change, one test, every time.

Before you call a teacher

Three sources first: 1. this loop, top to bottom · 2. your schematic — does the build really match the drawing? · 3. a neighbor. Asking a neighbor isn't cheating; it's engineering.

Call for help like an engineer

Report findings, not feelings. "Power's good, the loop traces all the way around, but I'm suspicious of node B" gets you fast help. "It doesn't work" gets you lovingly sent back to step 1.

The usual suspects

Most dead circuits in this room are one of three things: a leg not seated deep in its row · an LED in backwards · a power supply that's off, flat, or sneakily switched to 3.3 V.

Multimeter upgrades · unlocked in lesson 4

Once you've learned the meter, three moves supercharge the loop:

Power check (step 2) — probe red wire to black wire. Reads 5 V? Power's innocent; move on.
Node check (step 4) — continuity beep between two points that should be the same node. No beep = you found the bug.
Drop check — voltage across each component in the loop. The drops always add up to the supply's voltage, so the component hogging all the volts (or getting none) is your suspect.