Technician Track · Breadboard Lab

Electronics Lab

Build real circuits on a solderless breadboard: resistors, LEDs, capacitors, transistors, a MOSFET, a 555 timer, a buzzer and a light sensor, measured with a multimeter and a two-channel scope. A circuit solver, checked against SPICE, runs them in time: LEDs blink with the computed current, capacitors charge on the scope, and parts driven past their ratings fail, then the lab explains why. Switch to Missions for twelve Technician bench tasks that check themselves. For a fixed circuit with sliders, try the Circuits Lab.

Breadboard · 830 points · 0.1 in pitch
Multimeter—
Supply—
LEDs—
Hottest resistor—
Status—

OscilloscopeDC steady state
CH1unclipped
CH2unclipped
Time

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What this lab teaches

Everything a Technician-class ham or a new CET does at the bench: wire a circuit from a schematic idea, limit an LED's current with Ohm's law, read volts, amps and ohms the right way, and recognise the mistakes that smoke parts and blow meter fuses.

ETA 2Electrical theoryOhm's law, power, voltage dividers ETA 3Electronic componentsResistor colour codes and ratings, diodes, LEDs ETA 4Series and parallel circuitsCurrent paths on a breadboard ETA 8Test equipmentMeter in parallel for volts, in series for amps, unpowered for ohms ETA 3Transistors and the 555Switching, saturation, RC timing, astable and monostable TechAmateur Technician examElectrical principles, components and circuits

Building from the keyboard

TabFocus the breadboard ← ↑ → ↓Move the hole cursor (Shift: 5 holes); connected holes light EnterPlace the chosen part, or select what is in the hole RRotate DeleteRemove the selected part SpacePress the selected button, flip the selected switch + −Turn the selected pot Ctrl Z / Ctrl YUndo, redo VFlat or 3D view PRun or pause time ← →On the scope screen: move the time cursor EscCancel
TextThe circuit as a netlist
    MethodHow the solver works, and its limits

    The board becomes a netlist: each five-hole strip and each rail is one node, and jumper wires join nodes. The solver writes Kirchhoff's current law at every node (nodal analysis) and solves it with Newton–Raphson, because diodes and LEDs are nonlinear: I = IS(eV/nVT − 1) with a series resistance. Junction steps are limited as in SPICE, and if a circuit will not settle the solver retries with gmin stepping and then source stepping. Ten test circuits, up to 21 LEDs at once, agree with ngspice 42 to better than 0.02%.

    Each LED is fitted to its datasheet's typical forward voltage at 20 mA (Kingbright WP7113 series: red 1.85 V, yellow 2.0 V, green 2.2 V, blue and white 3.3 V). Above its 30 mA absolute maximum the lab warns; at twice that the LED burns open. Resistors are ¼ W: above the rating they run hot, and past 6.25× (the 5 s short-time overload of IEC 60115-1) they burn open. Batteries have internal resistance (AA alkaline 0.15–0.3 Ω per Energizer's E91 datasheet; a 9 V PP3 is modelled at 1.7 Ω). The meter has a 10 MΩ volts input, a 1.8 Ω milliamp shunt behind a 440 mA fuse, and measures ohms by pushing its own test current.

    Time: capacitors use a second-order (Gear 2) integration step of 1/100 of the shortest RC time constant, and the lab runs in real time where the computer keeps up, slowed (and labelled) where it cannot. RC charge and discharge agree with ngspice 42 within 0.001% at a fine step and 0.03% at the lab's step. The 2N3904 and 2N3906 use the Gummel–Poon parameters of the Fairchild/onsemi SPICE model cards and match ngspice's operating points in cutoff, active and saturation; the 2N7000 is a level-1 MOSFET fitted to its datasheet, with its body diode. The NE555 is a behavioural model of TI's block diagram: a 3 × 5 kΩ divider, comparators at 1/3 and 2/3 of the supply, a flip-flop, the discharge transistor and the output stage; its astable and monostable timing match the datasheet formulas within 1%. Electrolytics vent after 2 s reversed beyond 1.5 V or above their surge rating. The scope's ground clip is the supply negative, and each probe loads its node with 10 MΩ, as a ×10 probe does.

    Not modelled: temperature, so a part burns the instant it passes its limit instead of after seconds; breadboard contact resistance; LED reverse breakdown (the lab warns above the 5 V rating instead); battery discharge over time; transistor and capacitor parasitics (junction capacitance, ESR, leakage).