MicroTrainer Series and Parallel
Simple Circuits

Simple Circuit Current Measurement

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What You’ll Learn

  • How to select the correct current range on a digital multimeter

  • The difference between amps, milliamps, and microamps

  • Why current must be measured in series

  • How to move the red meter lead to the proper input

  • How to avoid blowing the meter fuse

  • How to measure current in simple, series, and parallel circuits

  • What the readings tell you about circuit operation

Understanding Current Measurement

Current is the flow of electrons through a circuit, and we measure it in amperes (A). Many circuits—especially those using LEDs—operate in milliamps (mA).

When you measure current with a multimeter, the electricity actually flows through the multimeter. Because of this:

  • The meter must be placed in series

  • The red lead must be in the correct input (A or mA/µA)

  • The meter’s fuse must be protected by choosing the correct range

This is why having a rough idea of expected current is important before making the measurement.

Setting Up the Multimeter

  1. Turn the rotary switch to the milliamp (mA) setting.

  2. Use the yellow button (or equivalent) to select DC current.

  3. Move the red lead into the mA/µA input.

  4. Leave the black lead in the COM port.

  5. Confirm the fuse rating on your meter (commonly ~400 mA for the mA input).

Measuring Current on the Microtrainer

To measure current, the meter must become part of the circuit. This means inserting it in line with the component or switch.

Example: Simple Circuit

  • Place the red lead on the B+ pad.

  • Place the black lead on the pad after the switch.

  • This bypasses the switch so the current flows through the meter.

  • Result: The LED illuminates and the meter displays the current (e.g., ~3.18 mA).

Series Circuit Example

  • Measure at the B+ of the series section.

  • Place the second lead after the switch.

  • Both LEDs illuminate with a lower current (~1.41 mA).

Parallel Circuit Example

  • Measure at B+ for the parallel circuit.

  • Touch either branch of the LED pair.

  • Both LEDs illuminate, and the measurement is higher (~6.38–6.39 mA).

Small variations are normal and reflect meter precision.

Why Polarity Matters

Reversing the leads will still give a measurement, but it will show a negative value.
Using proper polarity (red toward battery positive, black toward battery negative) provides consistent, readable results.

Remember:

  • Current measurements place the meter in the path of electricity.

  • The meter fuse protects the meter—choose the correct range to avoid blowing it.

  • Current flow readings differ between simple, series, and parallel circuits.

  • This measurement technique is used everywhere in electrical troubleshooting.