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LED Circuit Design and Testing

Aug 30, 2025

Overview

This lecture covers the design, construction, and testing of a simple LED circuit with a switch, focusing on schematic design, breadboard assembly, and proper use of a multimeter to measure voltage, resistance, and current.

Schematic Design and Circuit Overview

  • The circuit turns an LED on or off using a switch.
  • Power is supplied by a 9V battery, with the positive and negative terminals indicated by schematic symbols.
  • An LED is connected in series with a resistor (calculated based on LED and battery specifications).
  • A 240Ξ© resistor is recommended, but a 270Ξ© can be used depending on availability.
  • The switch used can be a single pole single throw (SPST), but a double pole double throw (DPDT) switch can be adapted if necessary.

Materials and Breadboard Assembly

  • Materials: breadboard, 9V battery and connector, LED, resistor, switch (DPDT or SPST), wire, multimeter.
  • The longer leg (anode) of the LED connects to the positive rail; the shorter leg (cathode) to the resistor.
  • The resistor connects to the switch, which then connects to the battery’s negative terminal.
  • Carefully check all connections to avoid shorts before powering the circuit.
  • The switch controls current flow: ON closes the circuit, lighting the LED; OFF opens the circuit.

Understanding and Using the Multimeter

  • An auto-ranging multimeter with manual range option is recommended for flexibility.
  • Black probe goes to the common port; red probe switches ports depending on measurement (volts/ohms/hertz, amps, milliamps, or temperature).
  • Always set probes to the correct ports before measuring to avoid damage.

Measuring Circuit Values

  • Resistance: Measure by touching probes to each end of the resistor (unit: ohms).
  • Voltage: Set multimeter to voltage, connect red probe to positive side and black to negative side of a component; circuit must be powered.
    • Example: LED voltage drop ~3.14V; resistor voltage drop ~5.4V.
  • Current (Amps): Move red probe to amp/milliamp port; set dial accordingly.
    • Break the circuit and insert the multimeter in series where current flows.
    • Start with highest amp setting to avoid damage.
    • Example: Circuit current ~20mA (milliamps), measured by making the multimeter part of the circuit.

Key Terms & Definitions

  • Schematic β€” a diagram showing electrical connections using standard symbols.
  • Breadboard β€” a tool for building circuits without soldering.
  • Single Pole Single Throw (SPST) Switch β€” a basic on/off switch with two terminals.
  • Double Pole Double Throw (DPDT) Switch β€” a switch with six terminals, can be adapted for SPST use.
  • Auto-Ranging Multimeter β€” a device that automatically selects measurement range.
  • Amperage (Current) β€” the flow of electrical charge, measured in amps (A).
  • Voltage β€” the potential difference between two points, measured in volts (V).
  • Resistance β€” opposition to current flow, measured in ohms (Ξ©).
  • Burden Voltage β€” a small error voltage introduced by the multimeter while measuring current.

Action Items / Next Steps

  • Review how to calculate proper resistor values (refer to previous tutorial #7 if needed).
  • Practice setting up and measuring values (voltage, current, resistance) using a multimeter.
  • Stay tuned for the next lecture on interpreting measured circuit values.

Full transcript