Understanding Voltage in a Circuit

This lesson walks through how to measure voltage in a simple circuit using the Microtrainer Series & Parallel Card. Students will see how voltage appears at different points in the circuit, how components affect voltage levels, and why voltage drop testing is an essential diagnostic skill in automotive electrical systems.

Learning Goals

By the end of this lesson, students should be able to:

• Identify DC vs. AC voltage settings on a multimeter

• Properly place meter leads when measuring voltage

• Understand the concept of potential difference

• Measure source voltage (battery voltage)

• Measure voltage before and after a switch, resistor, and LED

• Perform voltage drop tests across individual components

• Interpret voltage changes to understand how the circuit is functioning

Required Tools & Equipment

• Microtrainer Series & Parallel Circuit Card

• Digital multimeter (Fluke 15B+ or similar)

2. Turning on the Microtrainer

• Turn the master switch ON.

• Turn the simple circuit switch ON to power the LED.
  The LED should now illuminate, showing the circuit is active.

3. What You’re Actually Measuring: Potential Difference

Voltage is always measured between two points.
When you measure voltage, you’re seeing how much electrical pressure exists from one point to another.

The most common starting point is from Battery Positive to Ground.

4. Source Voltage Measurement (Battery Simulation)

Place your leads like this:

• Red → Battery Positive (B+)

• Black → Ground (GND)

On the Microtrainer, this should read about 5 volts, which simulates a vehicle’s 12.6 volts on a healthy battery.

This measurement evaluates the battery’s ability to provide energy for the rest of the circuit.

5. Measuring After the Switch

Now check the voltage on the output side of the switch.

• Keep black on Ground

• Move red to the right side of the switch

You should see very close to 5 volts, showing that the switch is providing full system voltage when closed.

To check for differences between the switch input and output, measure between them:

• Red → Before the switch

• Black → After the switch

This will show very little voltage, meaning the switch has no significant resistance.

6. Voltage Before and After the Resistor

Before the resistor

• Voltage will still be near 5 volts.

After the resistor

• Expected reading is around 1.8–2.0 volts.

This drop occurs because the resistor and LED share the remaining voltage.

7. Performing a Voltage Drop Test

Voltage drop testing shows how much voltage is used by a specific component.

Across the Resistor

• Red → Before the resistor

• Black → After the resistor

• Expected drop: About 3 volts

Across the LED

• Red → Before the LED

• Black → After the LED

• Expected drop: About 1.8 volts

The resistor and LED together use the entire 5 volts before the circuit reaches ground.

This follows the principle:

All of the source voltage must be dropped across the components before the current returns to ground.

8. Understanding the Complete Voltage Path

Starting at 5V source:

• Switch: ~0V drop

• Resistor: ~3V drop

• LED: ~2V drop

• Back to ground: 0V

The total drop equals the source voltage.

This is how technicians verify circuit health and diagnose issues such as excessive resistance, poor grounds, and failing components.