Pico.Lab – A Closer Look at the PCB Design of a Web-GUI Embedded Multitool

Introduction

In the world of embedded development, having a collection of reliable debugging tools can make a significant difference in the development process. An oscilloscope, logic analyzer, adjustable power supply, UART terminal, and I2C/SPI interface are among the instruments that developers frequently need when working with microcontrollers and electronic circuits. However, carrying several individual instruments is not always practical, especially for hobbyists and developers working with limited desk space.

This is where Pico.Lab – Web-GUI Embedded Multitool, developed by CoretechR, becomes an interesting project.

Pico.Lab is an open-source embedded debugging platform built around the Raspberry Pi RP2350 microcontroller. It combines several essential laboratory instruments into a compact custom PCB, with its entire user interface accessible through a web browser over a USB connection. What makes this project particularly interesting is not just its software implementation, but also its hardware architecture and PCB design.

The project provides an excellent example of how a relatively inexpensive microcontroller can be transformed into a versatile development instrument through thoughtful hardware integration. In this review, I will focus primarily on the PCB design, component selection, circuit architecture, and several engineering considerations that make this project worth studying, particularly for anyone interested in designing custom electronics using KiCad.

1. Hardware Architecture and Overall Design Philosophy

 

One of the most important decisions in Pico.Lab is the use of the RP2350B instead of relying exclusively on a standard Raspberry Pi Pico board.

The RP2350B offers a larger GPIO count and eight ADC inputs, compared with the four ADC inputs available on the more common RP2350A variant. This is particularly useful because Pico.Lab needs to handle multiple analog measurement channels while simultaneously monitoring the voltage and current of its power rails.

The custom PCB expands the capabilities of the microcontroller considerably. Its main hardware features include:

• Four analog input channels with input protection and operational amplifier buffering.

• Eight configurable digital input/output channels.

• Dedicated UART, SPI, and I2C interfaces.

• Adjustable power output from approximately 1V to 5V.

• Current monitoring for the 5V, 3.3V, and adjustable power rails.

• Support for external digital logic levels.

• ESD, overvoltage, overcurrent, and reverse-current protection.

What I particularly appreciate about this architecture is that the board is not simply a breakout board for the RP2350. Instead, it is designed as a complete measurement and debugging platform.

The distinction is important: every additional instrument introduces new electrical requirements, and integrating all of them into one PCB requires careful consideration of signal integrity, power distribution, component placement, and grounding.

2. KiCad PCB Design and Four-Layer Architecture

The PCB design is arguably one of the most interesting aspects of Pico.Lab.

According to the project documentation, the designer opted for a four-layer PCB to accommodate the relatively high component count while maintaining a compact physical layout.

This is a sensible decision. A board combining four analog measurement channels, sixteen digital signal connections across multiple interfaces, power conversion, current sensing, and an RP2350B requires considerably more routing resources than a conventional microcontroller development board.

A four-layer PCB provides several advantages:

First, improved routing flexibility. Dedicated internal layers can be used for ground and power distribution, reducing the need to route every signal through the top and bottom layers.

Second, better ground-plane continuity. A reasonably continuous ground reference beneath signal traces helps provide predictable return-current paths. This is particularly important for analog measurement circuits and high-speed digital signals.

Third, improved electromagnetic compatibility. A carefully arranged ground and power structure can help reduce coupling between switching regulators, digital logic, and sensitive analog circuitry.

However, using four layers does not automatically guarantee good signal integrity. The actual result depends on how the designer assigns the layers, routes critical signals, and manages return currents.

For a project such as Pico.Lab, I would particularly want to see a clear separation between the analog front-end, digital interface circuitry, and switching power supply section.

The analog input circuits should ideally have short connections between their input connectors, protection components, buffer amplifiers, and ADC inputs. Meanwhile, switching regulator nodes and their associated high-current loops should be kept away from sensitive analog sections.

The four-layer approach provides the necessary flexibility to achieve this without excessively increasing the board dimensions.

Another positive aspect is the use of a custom PCB rather than simply attaching multiple breakout modules. Integrating everything on a single board reduces unnecessary wiring, improves mechanical reliability, and allows the designer to optimize the overall component arrangement.

3. Analog Front-End: Four-Channel Oscilloscope

The analog front-end is one of the most important sections of this PCB because it directly determines the usefulness of the oscilloscope functionality.

Each of the four analog channels uses a high-input-impedance buffer amplifier followed by an RC filter before reaching the RP2350 ADC.

The circuit also incorporates input protection components, allowing the board to measure signals with an input range of approximately 12V.

This is a practical approach for a low-cost embedded oscilloscope.

The input buffer prevents the external circuit under measurement from being excessively loaded by the ADC input network. It also provides a degree of isolation between the external signal source and the microcontroller.

The RC filter serves two purposes: limiting unwanted high-frequency components and helping control noise entering the ADC. The series resistor also helps isolate the op-amp output from the capacitive load presented by the ADC input and filter capacitor.

An interesting detail is the use of the TLV9004 quad operational amplifier in the analog front-end. Using a quad op-amp is a reasonable way to implement multiple channels while keeping component count and PCB area under control.

Nevertheless, there are some limitations worth mentioning.

The designer explicitly acknowledges that the current implementation does not support negative input voltages. This means the oscilloscope is primarily intended for positive-voltage measurements rather than general-purpose bipolar signal analysis.

For measuring audio signals, AC waveforms, or circuits with negative supply rails, this limitation becomes particularly noticeable.

A future PCB revision could benefit from an input conditioning stage that supports bipolar measurements. Possible approaches include a precision biasing network, an appropriately designed level-shifting amplifier, or a bipolar input stage with suitable protection.

It would also be interesting to see more detailed information about the input impedance, input capacitance, channel-to-channel crosstalk, and actual analog bandwidth.

These parameters are important because a nominal 12V input range alone does not fully describe the measurement performance of an oscilloscope.

4. Precision Reference and ADC Measurement Accuracy

Another thoughtful design decision is the addition of an LM4040 voltage reference connected to the RP2350 reference input.

Microcontroller ADC accuracy is influenced by several factors, including reference stability, supply noise, PCB layout, and the characteristics of the analog input circuitry.

By providing a dedicated voltage reference, the designer aims to improve measurement consistency compared with relying entirely on the microcontroller's supply voltage.

This is particularly relevant because the ADC channels are used not only for oscilloscope measurements but also for monitoring the board's power rails.

There is, however, an important PCB layout consideration here.

The voltage reference should be treated as a sensitive analog component. Its surrounding decoupling, ground connection, and routing should be carefully implemented to minimize interference from the switching regulator and digital circuitry.

The reference voltage trace should ideally avoid running alongside noisy switching nodes or high-speed digital signals.

I would also recommend keeping the reference circuitry physically close to the RP2350 reference input, minimizing unnecessary trace length and potential noise pickup.

These details may appear relatively minor, but they can have a meaningful impact on the consistency of ADC measurements.

5. Digital I/O and Level-Shifting Circuitry

The digital interface section is another area where Pico.Lab demonstrates thoughtful engineering.

Unlike a conventional Raspberry Pi Pico, which operates with fixed 3.3V GPIO logic, Pico.Lab is designed to interface with external systems operating at different logic voltages.

The project uses SN74LVC1T45DBV level translators for the configurable digital channels. These devices support bidirectional signal translation using an external target-side supply.

This allows the board to work with a wider range of embedded systems, with the documented hardware supporting logic voltages from approximately 1.65V to 5.5V.

Each configurable channel also includes a switchable pull-up resistor, making the digital interface more flexible when working with different types of circuits.

Dedicated UART and SPI connections use similar level-shifting arrangements, while I2C uses the PI4ULS5V202, a specialized translator suitable for open-drain communication.

I consider this an excellent example of choosing components according to the electrical requirements of each interface rather than attempting to use one universal level-shifting circuit for everything.

From a PCB design perspective, the digital connector arrangement is also important. The project places multiple rows of 2x4 pin headers along one edge of the board, providing convenient access to the measurement and communication signals.

This arrangement makes the board easier to connect to breadboards and external development boards without requiring a large number of individual breakout cables.

One possible improvement would be more prominent silkscreen labeling around the connectors. When sixteen digital channels and several dedicated communication interfaces are available, clear labeling becomes essential for practical usability.

6. Integrated Adjustable Power Supply

Perhaps the most ambitious hardware feature is the integrated adjustable power supply.

Instead of using a conventional adjustable regulator controlled directly through an analog feedback network, the designer selected the MP28167-A buck-boost converter.

The regulator is controlled through I2C, allowing the output voltage to be adjusted digitally from approximately 1V to 5V, with a reported adjustment resolution of 0.8mV.

This is an interesting design choice because it simplifies the control architecture while allowing the power supply to operate independently of the microcontroller's firmware execution.

Even if the RP2350 reboots or the firmware crashes, the regulator does not automatically lose its programmed output setting.

Since the regulator does not provide direct voltage and current readings through its registers, the designer added an external voltage divider and current-sense amplifier connected to the microcontroller ADC.

The board also monitors current consumption on its 3.3V and 5V rails.

Another useful addition is the LM66100 ideal diode, which protects the output rails against reverse-current conditions.

From a PCB engineering perspective, this section deserves particular attention.

Switching regulators generate high-frequency current loops, and their layout is critical to both efficiency and electromagnetic interference.

The input capacitors, switching components, output capacitors, and regulator ground connections should be positioned carefully according to the manufacturer's layout recommendations.

The switching node should be kept as compact as possible, with sensitive analog traces routed away from it.

I would also consider whether the adjustable output supply has sufficient filtering to prevent switching noise from affecting sensitive circuits connected to the board.

This is especially important because Pico.Lab is intended to function as both a power supply and a measurement instrument.

7. Mechanical Design, Connectors, and PCB Integration

The PCB is housed inside a custom 3D-printed enclosure consisting of upper and lower shells, with four M3 screws securing the assembly.

I particularly like the decision to integrate the PCB and enclosure as a single mechanical design rather than treating the enclosure as an afterthought.

The USB-C connector and boot button are positioned along the board edges, making them accessible without requiring the user to open the enclosure.

The boot button also has a dual purpose: it can be used to enter the USB bootloader mode and can be accessed by the firmware as a normal GPIO input.

This is a small but useful detail that demonstrates good integration between mechanical and electrical design.

The enclosure uses a transparent upper section, allowing the internal electronics to remain visible. It is an attractive presentation choice for a DIY laboratory instrument.

However, the designer also acknowledges that the small printed pin labels are not particularly easy to read. For a more polished production version, UV-printed labeling or a dedicated front-panel overlay would be worth considering.

8. PCB Improvements and Future Considerations

Although the overall hardware architecture is impressive, there are several areas that could be explored in future PCB revisions.

Analog performance: Adding bipolar input capability would significantly expand the usefulness of the oscilloscope, especially for audio and general electronics debugging.

Grounding strategy: More detailed documentation of the four-layer stack-up, ground-plane arrangement, and analog/digital return-current paths would help other KiCad users understand and reproduce the design.

Power supply noise: Additional investigation into switching ripple and output filtering could improve the adjustable power supply's suitability for sensitive embedded applications.

Input protection: The analog and digital input protection networks could benefit from published clamping characteristics and maximum safe input conditions. Users should understand the difference between the nominal measurement range and the absolute maximum voltage the board can withstand.

PCB documentation: Providing annotated PCB screenshots, layer-stack information, critical layout explanations, and manufacturing notes would make the project even more educational.

These are not necessarily flaws in the existing design. Rather, they are opportunities to improve an already interesting hardware platform.

9. Final Verdict

 

Pico.Lab is an excellent example of an embedded hardware project that goes beyond the typical microcontroller development board.

What makes it particularly interesting is the integration of multiple instruments into a single compact PCB without sacrificing the flexibility required for embedded development.

From a PCB design perspective, the most impressive aspects are the use of a four-layer architecture, the integration of multiple analog front-end channels, dedicated voltage-level translation, and the implementation of a digitally controlled adjustable power supply.

The selection of the RP2350B is also well justified, as its additional ADC inputs and GPIO availability make it suitable for a project with so many measurement and control functions.

I particularly appreciate that the designer did not simply combine several existing modules. Instead, the hardware was designed as an integrated system, with individual circuits selected according to their specific electrical requirements.

For KiCad enthusiasts, Pico.Lab is worth exploring not only as a finished project but also as a reference for learning how to organize a relatively complex embedded system on a four-layer PCB.

There are still opportunities for improvement, particularly in analog input flexibility, measurement accuracy, power supply noise management, and hardware documentation. Nevertheless, these considerations do not diminish the overall achievement.

It is also important to remember that Pico.Lab is designed as a convenient debugging multitool rather than a replacement for professional laboratory instruments. Its oscilloscope bandwidth is approximately 400kHz, and its logic analyzer supports capture rates of up to 100MS/s under the project's stated operating conditions.

Overall, Pico.Lab is a highly interesting open-source hardware project that demonstrates how thoughtful PCB engineering, component selection, and embedded software integration can turn an inexpensive microcontroller into a surprisingly capable development instrument.

For anyone interested in KiCad, embedded instrumentation, analog front-end design, or building custom laboratory tools, this project is definitely worth studying.

Project repository: https://github.com/CoretechR/PicoLab

License: GNU General Public License v3.0 (GPL-3.0)