Arduino Eelectronic Component Tester project is one of the most useful tools you can build for an electronics workbench. With a single Arduino Nano, three test terminals and an OLED display, this tester can automatically identify many commonly used components and display their values, type and pin configuration.

Unlike a basic continuity tester, this project performs several controlled electrical tests on the connected component. The firmware checks all possible terminal combinations, repeats the measurement three times, rejects unstable readings and displays a median result only when the measurements agree.

This guide explains the complete circuit, component connections, working principle, firmware configuration, assembly process, calibration procedure and safe operating method according to the supplied firmware. The code is designed for an ATmega328P-based Arduino Nano and an SSD1306 128×64 I2C OLED.

What Is an Electronic Component Tester?

An electronic component tester is a microcontroller-based measuring device that automatically detects the type and pin arrangement of an unpowered electronic component.

Depending on the detected part, this tester can display:

• Resistance
• Capacitance
• Inductance
• Capacitor ESR
• Capacitor loss
• Diode forward voltage
• Diode junction capacitance
• BJT transistor type
• Transistor pinout
• Transistor current gain or hFE
• Base-emitter voltage
• MOSFET or JFET type
• MOSFET gate threshold voltage
• MOSFET gate capacitance
• Thyristor pinout
• Triac pinout

The original AVR transistor-tester concept was developed by Markus Frejek and subsequently expanded by Karl-Heinz Kübbeler and other contributors. Later versions became capable of testing more than transistors, which is why the device is now commonly called a component tester.

Circuit Diagram

Components Required

For the most accurate resistance and capacitance measurements, use precision resistors and enter their individually measured values into the firmware.

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How Does This Arduino Component Tester Work?

The Arduino applies different voltage and resistance combinations to three test terminals. It then measures the resulting voltages with the ATmega328P ADC. By comparing conduction direction, voltage drop, charging time and current-related values, the firmware identifies the connected component, calculates its parameters and determines its pinout.

The ATmega328P includes a 10-bit analog-to-digital converter and configurable bidirectional I/O ports. These features allow each test terminal to be driven high, driven low or left in a high-impedance input state during the identification process.

Main Features of This Electronic Component Tester

This firmware provides several improvements over a simple one-pass Arduino tester:

The default stability tolerance is 3%, and it can be adjusted between 2% and 10%. Results remain visible for approximately 15 seconds before the tester returns to its idle screen.

Components the Tester Can Identify

Resistors

The tester determines the connected test-pin pair and displays the resistance. It can also identify certain three-terminal resistor networks.

For a single resistor-like component, the firmware may additionally perform an inductance measurement. This is useful when testing coils or low-resistance inductors.

Capacitors

For capacitors, the tester can display:

• Capacitance
• Connected test pins
• Equivalent series resistance
• Dielectric loss value

Small parasitic capacitances are compensated using the open-probe zero calibration.

Diodes and LEDs

The tester identifies diode polarity and displays:

• Anode terminal
• Cathode terminal
• Forward voltage
• Junction capacitance

Multiple diode junctions may also be detected. LEDs that conduct within the tester’s available voltage and current range are normally identified as diodes, although high-forward-voltage LEDs may not produce a reliable result.

BJT Transistors

The firmware distinguishes between NPN and PNP bipolar transistors and displays:

• Emitter
• Base
• Collector
• hFE or DC current gain
• Base-emitter voltage

MOSFETs and JFETs

The tester supports N-channel and P-channel field-effect devices. Depending on the detected mode, it can display:

• Source
• Gate
• Drain
• Enhancement or depletion mode
• Gate threshold voltage
• Gate-source capacitance
• Drain current
• Gate-source test voltage

Thyristors and Triacs

For a thyristor, the tester identifies the cathode, gate and anode.

For a triac, it identifies MT1, gate and MT2. The current firmware reports the device and pinout but does not show an additional numeric parameter for these two component types.

These result formats are defined directly in the supplied firmware’s component-display function.

How the Measurement Circuit Works?

Each of the three test terminals has three important connections:

1. A direct analog connection to the Arduino
2. A connection through a nominal 680Ω low-range resistor
3. A connection through a nominal 470kΩ high-range resistor

The direct analog connections are A0, A1 and A2. The six resistor-control lines use digital pins D8 through D13.

The Arduino changes these pins between input and output states. It can therefore:

• Pull a terminal toward 5V through 680Ω
• Pull a terminal toward ground through 680Ω
• Pull a terminal toward 5V through 470kΩ
• Pull a terminal toward ground through 470kΩ
• Drive a terminal directly where required by the test routine
• Leave a terminal in a high-impedance measurement state
• Measure the voltage at the terminal

Arduino’s port mapping identifies digital pins D8–D13 as Port B, which matches the firmware’s use of the lower six Port B bits for RL1, RH1, RL2, RH2, RL3 and RH3.

Why Are Both 680Ω and 470kΩ Resistors Used?

The two resistor ranges allow the tester to work with components having very different impedances.

The 680Ω resistors provide a stronger test current for:

• Low and medium resistance measurements
• Semiconductor junction testing
• ESR measurement
• Transistor testing
• Inductance-related tests

The 470kΩ resistors provide a much smaller current for:

• High resistance measurements
• Capacitor charging-time measurements
• MOSFET gate tests
• High-impedance semiconductor checks

The original TransistorTester documentation describes separate resistance-measurement methods using the 680Ω and 470kΩ precision resistors.

Why the Tester Takes Three Measurements?

Many basic component testers display the result from a single test cycle. This firmware instead takes three complete measurement snapshots.

After the three passes, the software checks two conditions.

First, all three passes must identify the same:

• Component category
• Component mode
• Diode count
• Resistor count
• Pin arrangement

Second, the measured numerical values must remain within the configured stability percentage.

If either test fails, the OLED displays an unstable-contact warning and rejects all three readings. When the results are stable, the firmware calculates the median numerical values and displays the accepted result.

This method helps reduce the effect of:

• Loose component leads
• Oxidized terminals
• Probe movement
• Electrical noise
• ADC fluctuation
• Poor solder joints
• Human contact with the probes

OLED Memory Optimization

The project uses this U8g2 constructor:

U8G2_SSD1306_128X64_NONAME_1_HW_I2C oled(
    U8G2_R0,
    U8X8_PIN_NONE
);

U8G2_SSD1306_128X64_NONAME_1_HW_I2C oled(
    U8G2_R0,
    U8X8_PIN_NONE
);

The _1_ section selects a paged display buffer rather than a full-screen buffer. U8g2 constructors specify the display controller, communication method and buffer configuration.

A full 128×64 monochrome frame requires 1,024 bytes. The classic Arduino Nano has only 2KB of SRAM, so allocating half of the available memory to the OLED would leave too little space for the firmware’s three measurement snapshots, variables and calibration data. The page-buffer approach reduces SRAM usage while retaining the full display resolution.

Complete Arduino Nano Pin Connections

Test Terminal Connections

This mapping follows the firmware definitions:

• TP1, TP2 and TP3 are Port C bits 0, 1 and 2
• RL1 and RH1 are Port B bits 0 and 1
• RL2 and RH2 are Port B bits 2 and 3
• RL3 and RH3 are Port B bits 4 and 5

On the Arduino Nano, A0–A2 correspond to these ADC inputs, while Port B bits 0–5 correspond to D8–D13.

OLED Connections

The standard I2C pins on the classic Arduino Nano are A4 for SDA and A5 for SCL.

The code uses:

#define OLED_I2C_ADDRESS 0x3C
#define OLED_I2C_CLOCK 400000UL

#define OLED_I2C_ADDRESS 0x3C
#define OLED_I2C_CLOCK 400000UL

Therefore, the expected OLED address is 0x3C, and the firmware requests a 400kHz I2C bus.

Test Button Connections

The code configures D7 as a normal input and expects an external pull-up resistor. Pressing the button pulls D7 low.

Power-Supply Connections

For a battery-powered version:

Suggested capacitor placement:

• 100µF from the 7805 input to ground
• 47µF from the 7805 output to ground
• 0.1µF ceramic close to the regulator or Arduino supply pins

Observe the polarity of both electrolytic capacitors.

The L7805 is a fixed 5V positive regulator. The Arduino Nano documentation also permits a regulated 5V supply to be connected through its 5V power pin.

Important: Keep the battery power switched off while connecting the Nano to USB for programming unless the power system includes proper isolation or source selection.

Step-by-Step Assembly Guide

Step 1: Measure the Six Precision Resistors

Before soldering, use a reliable digital multimeter to measure each resistor separately.

Record the values as:

• RL1
• RH1
• RL2
• RH2
• RL3
• RH3

Do not assume all three nominally identical resistors have exactly the same value.

Example:

RL1 = 679.6Ω
RL2 = 681.1Ω
RL3 = 678.9Ω

RH1 = 469.7kΩ
RH2 = 471.2kΩ
RH3 = 470.4kΩ

RL1 = 679.6Ω
RL2 = 681.1Ω
RL3 = 678.9Ω

RH1 = 469.7kΩ
RH2 = 471.2kΩ
RH3 = 470.4kΩ

Step 2: Mount the Arduino Nano Headers

Solder female header strips to the veroboard so that the Arduino Nano can be removed later.

Using headers makes it easier to:

• Replace the Nano
• Reprogram the board
• Inspect solder joints
• Reuse the Nano in another project
• Modify the onboard D13 LED circuit if required

Step 3: Build the Power Section

Install the 7805 regulator, input terminal, switch and capacitors first.

Check the regulated output with a multimeter before installing the Nano. The output should be close to 5V.

Never insert the Arduino if the regulator output is significantly above 5V.

Step 4: Install the Three Test Terminals

Mount the three-pin connector in an accessible position and clearly label it:

TP1   TP2   TP3

TP1   TP2   TP3

Keep all wiring between the test connector, resistors and Arduino pins as short as practical. Long wires add parasitic resistance, inductance and capacitance.

Step 5: Install the Six Test Resistors

Connect each resistor to the correct digital pin and test terminal:

D8  -- 680Ω  -- TP1
D9  -- 470kΩ -- TP1

D10 -- 680Ω  -- TP2
D11 -- 470kΩ -- TP2

D12 -- 680Ω  -- TP3
D13 -- 470kΩ -- TP3

D8  -- 680Ω  -- TP1
D9  -- 470kΩ -- TP1

D10 -- 680Ω  -- TP2
D11 -- 470kΩ -- TP2

D12 -- 680Ω  -- TP3
D13 -- 470kΩ -- TP3

Do not interchange an RL and RH resistor. Incorrect placement can cause wrong component identification and inaccurate readings.

Step 6: Connect the Direct ADC Lines

Connect:

A0 directly to TP1
A1 directly to TP2
A2 directly to TP3

A0 directly to TP1
A1 directly to TP2
A2 directly to TP3

These connections should not include a series resistor unless the entire firmware and measurement calculations are redesigned for it.

Step 7: Connect the OLED

Connect the OLED to 5V, ground, A4 and A5.

Keep the I2C wires away from long test leads and the battery input wire.

Step 8: Connect the Push Button

Connect one side of the button to D7 and the other side to ground.

Install the 10kΩ resistor between D7 and 5V.

Step 9: Inspect the Veroboard

Before applying power, check for:

• Copper-track bridges
• Reversed electrolytic capacitors
• Incorrect 7805 orientation
• Open ground connections
• Swapped 680Ω and 470kΩ resistors
• Shorts between D8–D13
• Shorts between A0–A2
• Incorrect OLED wiring
• Incorrect battery polarity

Preparing the Arduino Code

Install the Required Library

The firmware uses:

#include <Wire.h>
#include <U8g2lib.h>

#include <Wire.h>
#include <U8g2lib.h>

Wire is normally included with the Arduino core. Install the U8g2 library through the Arduino IDE Library Manager.

Select the Correct Board

In the Arduino IDE, select:

Board: Arduino Nano
Processor: ATmega328P

Board: Arduino Nano
Processor: ATmega328P

Some clone Nano boards require:

Processor: ATmega328P (Old Bootloader)

Processor: ATmega328P (Old Bootloader)

Select the correct COM port before uploading.

Entering the Exact Resistor Values

The firmware stores the default test-resistor values using scaled integers.

680Ω Resistor Conversion

The RL values use units of 0.1Ω:

Firmware value = measured resistance in ohms × 10

Firmware value = measured resistance in ohms × 10

Example:

679.6Ω × 10 = 6796

679.6Ω × 10 = 6796

Enter it as:

#define DEFAULT_RL1_TENTH_OHM 6796U

#define DEFAULT_RL1_TENTH_OHM 6796U

470kΩ Resistor Conversion

The RH values use units of 10Ω:

Firmware value = measured resistance in ohms ÷ 10

Firmware value = measured resistance in ohms ÷ 10

Example:

469700Ω ÷ 10 = 46970

469700Ω ÷ 10 = 46970

Enter it as:

#define DEFAULT_RH1_TEN_OHM 46970U

#define DEFAULT_RH1_TEN_OHM 46970U

Configure all six values:

#define DEFAULT_RL1_TENTH_OHM 6796U
#define DEFAULT_RH1_TEN_OHM   46970U

#define DEFAULT_RL2_TENTH_OHM 6811U
#define DEFAULT_RH2_TEN_OHM   47120U

#define DEFAULT_RL3_TENTH_OHM 6789U
#define DEFAULT_RH3_TEN_OHM   47040U

#define DEFAULT_RL1_TENTH_OHM 6796U
#define DEFAULT_RH1_TEN_OHM   46970U

#define DEFAULT_RL2_TENTH_OHM 6811U
#define DEFAULT_RH2_TEN_OHM   47120U

#define DEFAULT_RL3_TENTH_OHM 6789U
#define DEFAULT_RH3_TEN_OHM   47040U

These defaults are copied into EEPROM when the existing calibration record is missing, incompatible, outside its permitted range or has an invalid CRC.

Important Firmware Settings

#define MEASUREMENT_PASSES 3
#define DEFAULT_STABILITY_PERCENT 3
#define MIN_STABILITY_PERCENT 2
#define MAX_STABILITY_PERCENT 10
#define RESULT_TIMEOUT_MS 15000UL
#define BUTTON_LONG_PRESS_MS 1500UL
#define CHARGED_COMPONENT_WARNING_MV 100U
#define MANUAL_DISCHARGE_REQUIRED_MV 300U
#define SAFE_DISCHARGE_LEVEL_MV 10U

#define MEASUREMENT_PASSES 3
#define DEFAULT_STABILITY_PERCENT 3
#define MIN_STABILITY_PERCENT 2
#define MAX_STABILITY_PERCENT 10
#define RESULT_TIMEOUT_MS 15000UL
#define BUTTON_LONG_PRESS_MS 1500UL
#define CHARGED_COMPONENT_WARNING_MV 100U
#define MANUAL_DISCHARGE_REQUIRED_MV 300U
#define SAFE_DISCHARGE_LEVEL_MV 10U

Measurement Passes

The code requires exactly three passes. Do not reduce this value without modifying the snapshot and median-processing logic.

Stability Percentage

The default tolerance is 3%.

A smaller value provides stricter validation but may reject more components. A larger value accepts more variation but may produce less repeatable measurements.

For a properly assembled tester, 3% is a suitable starting point.

Result Timeout

The displayed result remains visible for 15 seconds:

#define RESULT_TIMEOUT_MS 15000UL

#define RESULT_TIMEOUT_MS 15000UL

Increase this value when more reading time is required.

Uploading the Firmware

1. Turn off the external battery supply.
2. Connect the Nano to the computer through USB.
3. Open the firmware in the Arduino IDE.
4. Confirm the six measured resistor values.
5. Select the correct Nano board and processor.
6. Select the correct port.
7. Verify the sketch.
8. Upload the firmware.
9. Disconnect USB.
10. Switch on the regulated battery supply.

At startup, the OLED should display:

Component Tester
Circuit Diagrams
Firmware v2.2.1 OLED
SSD1306 OLED ready

Component Tester
Circuit Diagrams
Firmware v2.2.1 OLED
SSD1306 OLED ready

It then changes to the idle screen:

Component Tester
Connect to TP1-TP3
Short: TEST
Hold: Calibration

Component Tester
Connect to TP1-TP3
Short: TEST
Hold: Calibration

These startup and idle messages are defined in the supplied firmware.

How to Calibrate the Electronic Component Tester

Calibration should be performed after:

• Initial assembly
• Changing any test resistor
• Replacing the Arduino Nano
• Changing test sockets or leads
• Repairing the measurement section
• Observing incorrect low-resistance or capacitance readings

Opening the Calibration Menu

From the idle screen, press and hold the test button for approximately 1.5 seconds.

The calibration menu contains ten pages:

A short press moves to the next item. A long press selects the current item.

Editing a Calibration Value

Inside an editable setting:

• One short press increases the value
• A double press decreases the value
• A long press saves the value to EEPROM

The firmware permits:

• Stability: 2% to 10%
• RL values: 500.0Ω to 900.0Ω
• RH values: 350kΩ to 600kΩ

Open-Probe Calibration

Select Open/short zero, then hold the button.

The OLED instructs you to:

1. Remove every component from TP1, TP2 and TP3.
2. Keep all three terminals separated.
3. Hold the button to continue.

The firmware measures the small parasitic capacitance in six test directions and stores compensation values for the different terminal combinations.

Do not touch the test terminals during this step.

Short-Probe Calibration

After the open calibration, the OLED asks you to short TP1, TP2 and TP3 together.

Use a short, clean and low-resistance conductor.

Hold the button again. The tester verifies that all three probes are shorted and measures the zero-resistance or ESR offset for:

• TP1–TP2
• TP1–TP3
• TP2–TP3

The results are saved automatically in EEPROM.

Factory Reset

Select Factory reset and hold the button.

The tester asks for confirmation:

• Hold to confirm
• Tap to cancel

A factory reset restores the firmware’s compiled default resistor values, correction factors, ESR offsets and stability setting.

How to Use the Electronic Component Tester?

Testing a Two-Terminal Component

For a resistor, capacitor, diode, LED or inductor:

1. Disconnect the component from its circuit.
2. Discharge it completely when it is a capacitor.
3. Connect the two leads to any two different test terminals.
4. Leave the third terminal unused.
5. Press the button briefly.
6. Do not touch the component or test terminals.
7. Wait for all three measurement passes.
8. Read the accepted result.

The terminal order is not important because the firmware tests multiple directions automatically.

Testing a Three-Terminal Component

For a BJT, MOSFET, JFET, thyristor or triac:

1. Remove the component from its circuit.
2. Connect one lead to each test terminal.
3. Press the test button.
4. Keep the component stationary.
5. Wait for the final result.

The device determines the component pinout automatically.

Why Components Should Be Tested Out of Circuit?

Other components connected to the same circuit can create parallel paths and semiconductor junctions. These additional paths may cause:

• Wrong component identification
• Incorrect resistance readings
• False diode detection
• Incorrect transistor pinout
• Unstable-contact errors
• Failed capacitor measurements

This tester is designed for isolated, unpowered components. It is not a replacement for a protected digital multimeter and must never be connected to a live circuit. The ComponentTester project documentation gives the same safety warning because typical tester probes have no high-voltage input protection.

Charged-Capacitor Safety System

Before every measurement pass, the firmware reads the voltage on all three test terminals.

Below 100mV

The automatic discharge routine proceeds without showing a charged-capacitor warning.

Between 100mV and 300mV

The OLED shows a charged-capacitor warning and attempts to discharge the component through the measurement network.

At or Above 300mV

The measurement is stopped, and the user is instructed to remove power and discharge the component manually.

Final Safety Check

After automatic discharge, the voltage must fall to 10mV or less. Otherwise, the tester refuses to continue.

These thresholds improve safety but do not make the input voltage-protected. Always discharge capacitors externally before connecting them.

Understanding the OLED Results

Resistor Example

Resistor
Pins: 1-2
R=1.47kΩ

Resistor
Pins: 1-2
R=1.47kΩ

When inductance is detected, the fourth line may display:

L=...

L=...

Capacitor Example

Capacitor
Pins: 1-3
C=100µF
ESR=0.42Ω Loss=...

Capacitor
Pins: 1-3
C=100µF
ESR=0.42Ω Loss=...

NPN Transistor Example

NPN Transistor
Pins: E1 B2 C3
hFE=215
VBE=0.68V

NPN Transistor
Pins: E1 B2 C3
hFE=215
VBE=0.68V

MOSFET Example

N-E-MOSFET
Pins: S1 G2 D3
Vth=2.10V
Cgs=1.25nF

N-E-MOSFET
Pins: S1 G2 D3
Vth=2.10V
Cgs=1.25nF

Diode Example

Diode
Pins: A1 C2
Uf=0.67V
C=...

Diode
Pins: A1 C2
Uf=0.67V
C=...

Arduino Nano D13 Onboard LED Consideration

The firmware uses D13 as the RH3 control output through the third 470kΩ resistor. D13 is also the Arduino Nano’s built-in LED pin.

Because the RH3 path is a high-impedance 470kΩ measurement path, the onboard LED circuit on some Nano designs or clones can potentially influence measurements involving TP3. This is especially relevant when measuring high resistances or very small capacitances.

Removing the onboard “L” LED is not automatically required. Use this practical test first:

1. Calibrate the tester.
2. Measure the same known resistor between TP1–TP2.
3. Repeat between TP1–TP3.
4. Repeat between TP2–TP3.
5. Compare the three results.

When all pairs produce similar readings within the selected tolerance, leave the LED unchanged.

Consider removing or isolating the D13 LED only when:

• TP3 measurements differ consistently
• RH3 cannot be calibrated accurately
• High-resistance readings involving TP3 are unstable
• Small-capacitance results are noticeably different on TP3
• The Nano will be dedicated permanently to the tester

This is a hardware-dependent consideration because different Nano-compatible boards may use different LED and USB-interface circuits.

Improving Measurement Accuracy

Use Precision Resistors

Use at least 1% resistors. For a higher-quality tester, select 0.1% metal-film resistors.

The firmware can compensate for the exact value of each resistor, but it cannot fully correct:

• Excessive temperature coefficient
• Electrical noise
• Poor solder joints
• Unstable resistor construction
• Leakage across a dirty circuit board

Keep Test Wiring Short

Long test leads increase parasitic capacitance and resistance.

For accurate small-capacitance and low-resistance measurements:

• Use short terminal connections
• Avoid long jumper wires
• Keep solder joints clean
• Remove flux residue
• Keep the test terminals away from the power input

Use a Stable 5V Supply

The ADC and test-current calculations depend on the supply and internally measured reference values. A noisy or unstable supply can reduce repeatability.

Use:

• A properly regulated 5V supply
• Good ground routing
• Local bypass capacitors
• Short power wiring

Do Not Touch the Component During Testing

Your body introduces resistance, capacitance and mains-frequency noise. This is particularly noticeable when testing:

• Megohm resistors
• Picofarad capacitors
• MOSFET gates
• JFETs
• High-impedance semiconductor junctions

Clean Component Leads

Oxidized leads can cause the firmware to display:

Unstable Contact
Component changed
3 readings rejected
Then press TEST

Unstable Contact
Component changed
3 readings rejected
Then press TEST

Clean the leads and repeat the measurement.

Troubleshooting

OLED Does Not Turn On

Check:

• OLED VCC and ground
• A4 to SDA
• A5 to SCL
• OLED address
• 5V regulator output
• Solder joints
• Whether the display uses SSD1306 or a different controller

The firmware expects address 0x3C.

Tester Always Shows Unknown Part

Possible causes include:

• RL and RH resistors interchanged
• A0, A1 or A2 not connected
• Wrong D8–D13 order
• Poor test-terminal contact
• Powered or in-circuit component
• Damaged component
• Incorrect resistor values
• Excessive board leakage

Tester Shows Voltage Detected Without a Component

Check for:

• Residual charge on a capacitor
• Moisture or flux on the board
• Incorrect power wiring
• Short between a test terminal and 5V
• Damaged Arduino analog input
• Wrong resistor connection
• External electrical noise

Measurements Are Rejected as Unstable

Try:

1. Cleaning the component leads.
2. Tightening the test terminal.
3. Shortening the leads.
4. Repeating open/short calibration.
5. Checking the 5V supply.
6. Inspecting solder joints.
7. Increasing stability from 3% to 4% only when the hardware is otherwise correct.

Do not immediately increase the tolerance to 10%, because that can hide a real hardware problem.

Capacitance Reading Is Too High With Empty Probes

Run the open-probe calibration again.

Ensure:

• Nothing is connected
• Probes are separated
• Your hands are away from the terminals
• The board is clean and dry
• Test wiring is short

ESR Does Not Read Zero When Probes Are Shorted

Run the short-probe section of zero calibration using a clean, low-resistance conductor.

Wrong Transistor Pinout

Verify that:

• The transistor is removed from its circuit
• All three terminals make good contact
• The component is not internally damaged
• The device is not an unsupported compound module
• The test voltage is sufficient for that specific device

Project Limitations

This DIY electronic component tester is extremely useful, but it is not a laboratory LCR meter or semiconductor curve tracer.

Limitations include:

• It is intended for unpowered components
• It has no high-voltage input protection
• Accuracy depends on resistor quality and calibration
• Very low resistance is affected by terminal and wiring resistance
• Very small capacitance is affected by board capacitance
• Large capacitors take longer to discharge and measure
• High-forward-voltage LEDs may not test reliably
• Some power MOSFETs may not switch fully at the available test voltage
• Complex modules cannot be identified as a single standard component
• In-circuit testing is generally unreliable
• Thyristor and triac results provide identification and pinout rather than detailed power parameters

The alternative ComponentTester firmware documentation similarly notes that this kind of tester is not equivalent to a dedicated LCR meter and that capacitance and inductance measurements have practical limits.

Final Result

This Arduino Nano electronic component tester combines a simple measurement circuit with advanced firmware features normally missing from basic DIY testers.

Its strongest features are:

• Automatic pinout identification
• Three-pass measurement validation
• Adjustable stability filtering
• Median-result processing
• Charged-capacitor detection
• Automatic low-voltage discharge
• Individual calibration of all six test resistors
• Open-probe capacitance compensation
• Short-probe ESR compensation
• EEPROM storage with CRC validation
• Compact SSD1306 OLED interface

When assembled with precision resistors, short wiring and careful calibration, it becomes a practical workbench tool for identifying loose electronic components, checking salvaged parts and confirming component pinouts before using them in a circuit.

Frequently Asked Questions

Recommended Image Alt Text

Main project image:
Arduino Nano electronic component tester with SSD1306 OLED display

Circuit diagram:
Electronic component tester circuit diagram using Arduino Nano

Veroboard assembly:
DIY Arduino component tester assembled on double sided veroboard

Calibration image:
Electronic component tester open and short probe calibration

Testing a transistor:
Arduino electronic component tester identifying transistor pinout and hFE

Testing a capacitor:
Electronic component tester measuring capacitor value and ESR