Circuit Simulator: Fault Lab

Circuit Fault Lab is a DC circuit simulator for troubleshooting practice: find the fault in a resistor circuit with two virtual voltage probes, commit to a diagnosis, repair it, then measure again to verify.
Scope: 6 fixed DC resistor layouts; source and resistor values change only in sandboxes. There is no free-form wiring and no component library.
It does not model AC, capacitors, transients or semiconductors.

HOW A CASE WORKS
Each circuit troubleshooting case opens with a symptom, like a midpoint at the reference. Place the red and black probes on two nodes and read the calculated voltage between them. Swap polarity and record the readings that matter. Then choose the component that explains the evidence, or call the circuit healthy, and write down why. In a fault case, restore a component to nominal and repeat a reading that exposed the fault. In a healthy case, repeat an internal-node reading without replacing anything. A case is verified only when the circuit and your repeated readings match nominal behavior.

WHY IT IS DIFFERENT
Instead of a blank canvas, each case starts with a fixed circuit and a symptom to explain. Your first judgment is locked once saved, so it cannot be rewritten after you see more evidence. To try again, archive the attempt; the original judgment and evidence stay in your notebook. Circuit and electrical troubleshooting becomes observe, explain, verify instead of guess and replace.

WHAT YOU GET
- 24 original circuit cases: 21 fault cases covering open circuits, resistance drift, low-resistance faults, branch isolation, loading, bridge comparison and shared feed paths, plus 3 healthy-circuit cases where a surprising reading is expected
- Service notes in some cases, where voltage evidence alone cannot separate two components
- Branch current inspection, labelled as a simulation inspection rather than a meter reading
- A Learn tab of six principles: voltage difference and polarity, Ohm's law, series paths, parallel branches, Kirchhoff's current law, and testing before replacing

CIRCUIT SANDBOXES
Six sandboxes use the same layouts: a two-resistor divider, a three-section series chain, independent parallel branches, a loaded divider, a resistive bridge and a shared feed with two loads. Step the ideal DC source between 1 and 24 volts and each resistor in 100-ohm steps between 10 and 10,000 ohms, then probe any node pair.

WHO IT IS FOR
Electronics students working through DC circuits, hobbyists who want to reason about voltage drops, and technician trainees practicing a measure-first habit. It does not cover electrical troubleshooting of building wiring, motors or control panels.

FREE CASES AND DC LAB
The first 6 cases and the divider sandbox are free, with no sign-up. The optional one-time DC Fundamentals Lab purchase unlocks all 24 cases and 6 sandboxes. No subscription and no ads. Restore it with the same Google Play account.

NOTEBOOK AND PRIVACY
Measurements, first judgments, repairs and archived attempts are saved in a notebook on your device. No account, sign-in or cloud sync, so uninstalling the app may remove your records. Practice content works without a connection; purchasing and restoring need a store connection.

RELATED DC BASICS TOPICS
The exercises relate to selected ETA International EM1 DC Basics topics: Ohm's law, electronic measurements, series, parallel and series-parallel circuits. Watt's law is not taught, and this is not a complete exam preparation course. Source: https://www.etai.org/electronics.html

DISCLAIMER
Circuit Fault Lab is an independent learning app. It is not affiliated with or endorsed by ETA International (Electronics Technicians Association, International); the name is used only to identify related topics. Practice with an ideal model does not qualify anyone to work on live electrical equipment.

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