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Equivalent Resistance01:16

Equivalent Resistance

In circuit analysis, situations often arise where resistors are neither in series nor parallel configurations. To tackle such scenarios, three-terminal equivalent networks like the wye (Y) (Figure 1 (a)) or tee (T) and delta (Δ) (Figure 1 (b)) or pi (π) networks come into play. These networks offer versatile solutions and are frequently encountered in various applications, including three-phase electrical systems, electrical filters, and matching networks.
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Design Example: Frog Muscle Response01:14

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Implementation of high-resolution time-to-digital converter in 8-bit microcontrollers.

The Review of scientific instruments·2012
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Related Experiment Video

Updated: May 19, 2026

The Fabrication and Operation of a Continuous Flow, Micro-Electroporation System with Permeabilization Detection
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A microcontroller-based lock-in amplifier for sub-milliohm resistance measurements.

Lars E Bengtsson1

  • 1Department of Physics, University of Gothenburg, SE-412 96 Gothenburg, Sweden.

The Review of Scientific Instruments
|August 3, 2012
PubMed
Summary

A novel digital ohmmeter achieves high resolution (<60 μΩ) using a microcontroller and instrumentation amplifier. Its lock-in detection firmware enables precise measurement of low resistances without external signal generators.

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Area of Science:

  • Electrical Engineering
  • Instrumentation and Measurement

Background:

  • Accurate measurement of low resistances (micro-ohm range) is challenging.
  • Traditional methods often require complex circuitry or specialized hardware.

Purpose of the Study:

  • To present a novel, cost-effective digital ohmmeter design.
  • To achieve high-resolution resistance measurements using a general-purpose microcontroller.

Main Methods:

  • Design of a digital ohmmeter utilizing a microcontroller and instrumentation amplifier.
  • Implementation of a firmware-based lock-in detection technique.
  • Employing digital I/O pins to alternate current and discriminate signals.

Main Results:

  • Achieved a resolution of less than 60 μΩ.
  • Successfully detected microvolt drops across sample resistors as low as 55.6 μΩ.
  • Demonstrated selective detection of signals out of phase/frequency with the reference.

Conclusions:

  • The proposed design offers a simple yet effective solution for high-resolution digital ohmmeters.
  • It eliminates the need for external reference signal generators and powerful processors.
  • This approach is suitable for measuring very low resistances in various applications.