THE COMPLETE LEARNING PATH
Start with a loop. Build your intuition.
Work from charge flow and resistance toward energy storage, switching and sensing. Each of the 48 lessons has a guide and an interactive workbench. Explore in order or open the concept you need.
Circuit basics
9 lessonsOpen and closed circuits
A steady current needs a complete conducting path from one battery terminal, through the load, to the other terminal. Opening a switch interrupts that path.
Conductors and insulators
Materials differ in how easily charges move through them. A metal link offers low resistance; a dry insulating link offers a very large resistance.
Volts, amps and ohms
Voltage is a potential difference, current is charge flow per second, and resistance relates the two for an ohmic element at a fixed temperature.
Series and parallel circuits
Series loads share one current path. Parallel loads connect across the same two nodes and therefore share the same voltage.
Series and parallel cells
Identical cells in series add their voltages. An ideal parallel combination retains one cell’s voltage while sharing load current between cells.
Alternating and direct current
A DC source maintains one polarity. An AC source changes polarity with time; a sinusoid alternates smoothly between positive and negative voltage.
Breadboard connections
A solderless breadboard joins selected sockets underneath the surface. Five-hole strips typically stop at the central channel; power rails may be split.
Using a multimeter
A voltmeter reads potential difference across two points. An ammeter reads current through a path and must be inserted in series.
Kirchhoff’s circuit laws
Charge conservation gives the current law at a junction. Energy balance gives the voltage law around a closed loop under the lumped-circuit assumptions.
Resistors
8 lessonsHow resistance works
A resistor limits current and dissipates electrical energy as heat. The voltage drop depends on both resistance and the current through it.
Resistor colour codes
A four-band resistor encodes two significant digits, a multiplier and a tolerance. Read from the end with the first significant band.
Resistors in series
Every resistor in a single series path carries the same current. Its share of supply voltage is proportional to its resistance.
Resistors in parallel
Parallel resistors share the same pair of nodes. Each branch current follows its own resistance, and branch currents add at the source.
Voltage dividers
Two series resistors create a midpoint voltage relative to the lower node. An unloaded divider is a ratio, not a regulated power supply.
Variable resistors
A potentiometer has two ends and a movable wiper. With all three terminals it divides voltage; with two terminals it acts as a variable resistance.
Power and resistor heating
Power is the rate of energy transfer. A resistor dissipates P=VI; its power rating limits the permitted heating under specified conditions.
Wheatstone bridges
A bridge compares the midpoint voltages of two dividers. When their resistance ratios match, the detector sees zero differential voltage.
LEDs & diodes
5 lessonsLED polarity
An LED conducts mainly in its forward direction. A series resistor limits its current after the forward voltage has been accounted for.
LED colours and voltage
LED colour is related to the semiconductor bandgap. Different devices require different forward voltages, even when their packages look similar.
LED overcurrent
An LED is not a self-limiting load. A resistor or current driver controls current; exceeding a device’s rating can damage it.
Diodes and rectification
A diode is a direction-sensitive nonlinear device. A simple silicon model blocks reverse current and has an approximate forward drop when conducting.
LEDs in series
LEDs in one series branch share the same current. Their forward voltages add before calculating the voltage left for the limiting resistor.
Capacitors
9 lessonsThe capacitor tank analogy
A capacitor stores separated charge and energy in an electric field. A water tank provides an analogy for how stored charge can raise a voltage.
RC charging
Through a resistor, capacitor voltage approaches the supply exponentially. As the capacitor fills, the voltage across the resistor and charging current decrease.
RC discharge and fading
A charged capacitor can supply a load after its source is disconnected. In a linear RC model, capacitor voltage decays exponentially.
Transient capacitor current
Current into a capacitor depends on how quickly its voltage changes. At DC steady state, an ideal series capacitor blocks continuous current.
Combining capacitors
Parallel capacitors share voltage and their capacitances add. Series capacitors carry equal incremental charge and combine through reciprocal capacitances.
Rectifier smoothing
A reservoir capacitor charges near rectified peaks and supplies a load between peaks. Its voltage ripples rather than becoming perfectly constant.
RC timing thresholds
An RC ramp can cross a comparator threshold after a predictable delay. The capacitor and resistor set the ramp, while the threshold determines the switching instant.
Capacitor number codes
A common three-digit ceramic capacitor code uses two significant digits followed by a decimal multiplier in picofarads.
Two-transistor flasher
Cross-coupled transistor stages can alternate as capacitor voltages change. One branch turns on while the other recovers toward its switching threshold.
Switches & logic
4 lessonsMomentary push buttons
A normally open momentary button closes while pressed and opens when released. It is not the same behavior as a latching switch.
Latching slide switches
A latching switch retains its position after the user releases it. Its contacts select which of two LED branches is connected.
AND and OR switch logic
Two switches in series implement AND: both must close. Two parallel switches implement OR: either path can conduct.
Two-way lighting switches
Two changeover switches connect a lamp through one of two traveler wires. Toggling either switch changes whether a complete path exists.
Transistors
6 lessonsTransistor current control
In a simplified BJT model, a small base current controls a larger collector current. Collector current is also limited by the supply and collector load.
A transistor as a switch
A transistor can switch a load using a separate base-drive path. With enough drive, a BJT enters saturation and its collector-emitter voltage becomes small.
BJT current gain
DC current gain β is the collector-to-base current ratio in the active region. It varies among devices and with operating conditions.
NPN and PNP transistors
NPN and PNP BJTs use opposite voltage and current polarities. An NPN commonly switches near ground; a PNP commonly switches near the positive supply.
Darlington touch input
A Darlington pair connects two BJT stages to obtain high effective current gain. A tiny modeled touch current can therefore control a visible load.
Transistor NOT gate
A common-emitter transistor with a collector pull-up can invert an input. Driving the transistor on pulls the output low.
Sensors
7 lessonsLight-dependent resistors
An LDR usually has lower resistance under brighter illumination. In a divider, its changing resistance becomes a changing voltage.
Automatic night light
A light-sensitive divider and a threshold detector can switch a lamp as surroundings become dark. Divider orientation determines the direction of the voltage change.
Temperature and thermistors
An NTC thermistor decreases in resistance as temperature rises. Its nonlinear curve can be approximated using a beta parameter and a reference resistance.
Magnetic reed switches
A reed switch contains contacts that move in a magnetic field. It converts a nearby magnet’s field into an electrical open or closed state.
Temperature threshold alarm
A thermistor divider and a threshold detector can activate an alarm above a set temperature. The threshold compares a voltage derived from temperature.
Adjustable night light
An adjustable reference lets a light sensor switch at different illumination levels. The sensor value and threshold are separate inputs.
Hall-effect sensing
A Hall sensor responds electrically to magnetic flux density. A linear sensor can represent both field magnitude and polarity around a midpoint output.