The PCB layout is clearly labeled with reference designators that match the Bill of Materials (BOM), which makes the soldering process straightforward and well structured. By following the BOM component by component, using checkboxes to track progress it is easy to avoid missing parts or placing components incorrectly.

I approached the soldering process methodically, starting with smaller passive components and gradually moving to larger or more sensitive IC's. This sequence helps maintain good access to pads and reduces the risk of disturbing previously soldered parts.

For this step, using the right tools and setup is essential. I recommend:

• Good-quality flux and lead-free solder wire

• A fume extractor, or alternatively working in a well-ventilated area

• Adequate lighting, which is critical for inspecting solder joints

• A digital microscope (optional but highly recommended), as it helps identify solder bridges or cold joints that are difficult to detect with the naked eye.

Regarding the soldering iron, a 2–3 mm tip is generally ideal for this type of PCB, depending on individual skill level and comfort. In my case, I did not have a smaller tip available and successfully completed the assembly using a 4 mm tip, taking extra care with pad heating and solder control.

Kapton tape proved very useful when applying hot air, particularly to protect nearby components. I used a hot-air gun to preheat sections of the board, especially around larger components, to improve solder flow and reduce thermal stress.

To avoid damaging pads or components, I recommend keeping the soldering iron temperature in the 250–300 °C range. Staying within this window helps preserve PCB integrity while still achieving reliable solder joints. Once you are done soldering all components it is obligatory to give a final cleaning to the PCB with Isopropyl Alcohol (IPA), to remove any flux and solder residues that might cause  corrosion or shorts.

To verify that the assembled board is functioning correctly before full operation, Martin Loren included dedicated test points throughout the schematics. These test points are intentionally placed to simplify early validation of the power rails and key reference voltages.

For this step, the board must be powered using either 3.3 V or 5 V, depending on the selected power configuration. With the board powered on, a digital multimeter is used to probe the designated test points and measure the expected voltages.

The reference values and exact measurement locations are documented in the schematics discussed in Step 4. By comparing the measured voltages against the expected ones, it is possible to quickly confirm:

• Proper power distribution
  
  

• Correct operation of voltage regulators
  
  

• Stability of reference voltages (such as the virtual ground)
  
  

This step is crucial before connecting sensitive components or flashing firmware, as it helps detect issues such as incorrect component placement, solder bridges, or faulty power paths early in the build process. Performing ICT at this stage significantly reduces debugging time later and increases overall confidence in the hardware before moving on to functional testing and firmware integration.

After calibration, the final step is to verify that the oscilloscope operates correctly under real signal conditions. These functional tests validate the complete signal chain, from analog input, through sampling and processing, to visualization in the HScope application, using simple but effective test scenarios.

The tests below are based on the recommended USB-connection test procedures and focus on confirming signal acquisition accuracy, stability, and responsiveness.

Human Antenna Test (Quick Sanity Check)

One of the simplest sanity check and functional tests that can be performed is the so-called “Human Antenna” test. By leaving the probe input floating and lightly touching the probe tip with your finger, a sinusoidal-like waveform immediately appears on the screen.

This effect occurs because the human body acts as an antenna, coupling ambient electromagnetic fields into the oscilloscope input. These fields are primarily generated by the AC mains wiring inside building walls, resulting in a signal at:

• 50 Hz in Europe

• 60 Hz in America

Although this is not a precision measurement, it is an excellent first check to confirm that:

• The analog front-end is working

• The ADC is sampling correctly

• The signal path from input to display is functional

Known Voltage Signal Test

To further validate measurement accuracy, a known and stable voltage source can be connected to the oscilloscope input. Using a laboratory power supply or reference source, the measured voltage displayed in the app should closely match the applied value.

This test confirms:

• Correct calibration of the voltage multiplier

• Proper gain handling, especially at different vertical scales

• Stable readings without unexpected offset or drift

Frequency and Waveform Verification

Applying a low-frequency signal (for example from a signal generator or microcontroller PWM output) allows verification of:

• Correct waveform shape (sine, square, or triangle)

• Frequency measurement accuracy

• Trigger functionality and waveform stability

At this stage, both channels can also be tested independently or simultaneously if the HS402 license is enabled, to ensure consistent behavior across CH1 and CH2.

Overall Validation

Successfully completing these functional tests confirms that the oscilloscope is fully operational and ready for practical use. From simple signal probing to more advanced dual-channel measurements, the device demonstrates reliable acquisition, stable visualization, and predictable behavior, meeting the expectations for an educational and hobbyist-grade digital oscilloscope.

One of the strengths of this open-source project is its active and creative community. Engineers and makers from around the world have developed their own variants of the HS402 oscilloscope, along with complementary accessories and, most importantly, protective enclosures to improve usability and extend the lifespan of the PCB.

For this build, I selected a 3D-printed housing shared by the community on Thingiverse. The enclosure is compact, well-designed, and easy to assemble, while still providing adequate protection for the oscilloscope during everyday use. Its thoughtful layout allows straightforward access to connectors and controls without compromising structural integrity.

Because of its simplicity, robustness, and clean design, this enclosure is my personal recommendation for anyone building the HS402 DIY oscilloscope.

Behind, you can find:

• A link to the community-built HS402 oscilloscope variants, showcasing different design approaches and extensions

• A link to the STL files for this housing, allowing it to be 3D printed and assembled easily

• A link to Additional Modules you may find useful.

This final mechanical step completes the project, transforming the bare PCB into a portable and durable measurement instrument suitable for regular use.