When a single PCB does not meet your design needs, multi-board systems become necessary. Board-to-board connections depend on various connector types (such as mezzanine, pin header, edge connector), along with how they are aligned for signal integrity, to determine if your end product will be seamless or fall apart completely.

The connector type will largely determine the board to board connection. When it comes to mechanical stress during assembly, the board alignment must be precise. Even the slightest misalignment can result in poor electrical contact and/or early failure of a connection due to an inadequate connection time and/or temperature. Consider that shackles or mounting hardware (standoffs, screws) are required for an accurate spacing and that no flex should be introduced during assembly.

PCB with good alignment and connector type. Shackles or screws for accurate spacing.

PCB with good alignment

Signal integrity becomes increasingly difficult when transitioning through any method of connectors. To maximize signal integrity from the circuit to the connector, signal traces should always be kept as short and direct as possible. At any point in time, the geometry of the differential pairs should be observed and maintained when going into the connector. Additional vias and other components that can cause signal deterioration should be avoided near the connector. Finally, every high-speed connector has been designed to interleave ground pins to minimize the effects of crosstalk- therefore, utilize these pins with care.

PCB with interleaved ground pins

The way power is distributed among your components should also be considered. Do not use a single connection for the high current; try to use more connections to both lower resistance and lower heating in your system. To handle fast switching a good practice is to add local decoupling capacitors at the connectors on both boards to stabilize the voltage.

You should also consider how straightforward it is to join and separate two or more plates. Do you have pins or does each plate have a socket to make joining together easy? If you used connectors, will those connectors hold up to all of the assembled/disassembled action that will occur?

PCB with reliable board to board connections.

Summary: Multi-board systems do not only have an electric component, but also mechanical and common usage components. If you make good connections, you will end up with a fully functional system. If you make a bad connection, you will have a very expensive jigsaw puzzle.

Decoupling capacitors are invaluable components of reliable PCB design. They provide noise suppression, voltage stability, and keep your integrated circuits from operating chaotically.

Well placed decoupling capacitors

All digital integrated circuits will draw current in bursts when switching. Without local energy storage, this will create noise and voltage drops on the power rails. This is where decoupling capacitors come in. They are physically small capacitors connected in parallel with the power (Vcc) and ground (Gnd) that store charge at a local level. When a digital IC switches and requires current, the decoupling capacitor can provide the current immediately through a short trace instead of having to travel along a length of noisy power trace.

Decoupling capacitors should be placed very close to the IC's power + and ground - pins. Connecting the decoupling capacitor to the Vcc and Gnd using short traces is essential to limit inductance. If there are long traces connecting the decoupling capacitor to the Vcc and Gnd leads, inductance will increase; thus causing the decoupling capacitor to function poorly. Ideally, a via to a solid ground plane adjacent to the decoupling capacitor should be used.

Capacitor value is another important consideration. Many designers will use multiple values of decoupling capacitors in their designs:

Values of decoupling capacitors:

0.01 μF - 0.1 μF to suppress high-frequency noise

1.0 μF - 10.0 μF for low-frequency noise stability

Using small and large value capacitors assures that all frequencies between high and low are suppressed. Designers typically use decoupling capacitors of at least one 0.1 µF per power pin, and generally use bulk devices for low-frequency noise dampening.

Decoupling capacitors to suppress noise at high and low frequencies

The type of capacitor should be considered as well. Multi-layer ceramic (MLCC) capacitors are highly recommended; MLCC's have low ESR and ESL and are preferred for decoupling applications. Mount MLCC in accordance with their orientation, and keep them as close as possible to the IC.

PCB with multi-layer ceramic (MLCC) capacitors

Ground return is very important. Without a solid, continuous ground plane, decoupling won't work.

Decoupling capacitors are critical, not optional! Properly placed decoupling capacitors and proper capacitor values will yield a clean and stable operating circuit.

Backplane printed circuit boards handle many different types of high-speed connections between daughter cards, requiring strict layout discipline. Differential pairs should have controlled-impedance routing, and the stack-up should be consistent between all layers - every effort should be taken to minimize stubs using back-drilling as required. Via transitions should be well managed to help minimize reflections. Connectors should be aligned properly and spaced evenly, with higher pin counts having increased potential for crosstalk. Ground planes must be continuous to provide good return paths for signals. Mechanical and airflow concerns should also be considered during the design of a backplane, since they are typically used in cramped systems. A good backplane design will provide the most reliable signal quality/ integrity (SI), power distribution (PD) & mechanical reliability.

Two-dimensional layouts can be deceiving; however, the use of a three-dimensional (3D) PCB viewer in an electronic design automation (EDA) tool helps verify the heights of components as well as their alignment with connectors and fit into the housing (enclosure) prior to production. Using a 3D print model can also help in identifying other physical concerns such as possible collisions between tall components; inadequate edge clearance next to the edges; and misalignment of mechanical parts (housings/cases or heat sinks) and connections to the printed circuit board layout. Confirm all clearances for connectors, buttons, and mounting hardware. Properly routed PCBs can also fail mechanically if the 3D model has been ignored. Performing a simple 3D inspection prior to production will help eliminate expensive redesigns and assure proper fit and function of a PCB.

Today, we are taking a significant step forward into professional-grade system design. When I am designing a flight controller for high-value applications like expensive cinema cameras or critical long-range missions relying on a single, tiny hole to tell me how high the drone is, is a risk I am rarely willing to take.

The solution? Sensor Redundancy. I highly recommend integrating a Dual Barometer setup.

1. Why Using Two Barometers?

Why two barometers? As every seasoned embedded systems engineer knows, the question isn't if a sensor will fail, but when. Barometers are exposed to the environment. I have tried flying single-baro drones in challenging conditions, and I have seen them nearly crash because a tiny insect blocked the sensor port or a localized thermal pocket gave a false reading.

You can see in various robotics and automotive safety journals (like those from the IEEE Robotics and Automation Society) regarding fail-safe systems, which show that redundancy is the primary defense against localized sensor error. When your firmware (like Ardupilot) detects a discrepancy between two sensors, its Advanced Kalman Filter (EKF) can identify the erratic sensor, isolate it, and seamlessly switch the primary altitude source to the healthy barometer, all while the drone is in flight. Without redundancy, if one baro fails, the drone might violently shoot upward or crash into the ground.

2. Hardware Implementation: Taming the Dual SPI Bus

The biggest challenge in adding a second sensor is pin management. If you used I2C for both barometers, you would run into address conflicts unless you used two separate I2C buses, wasting precious MCU resources.

This is where my previous advice on using SPI really pays off. SPI is a "bus" protocol. As seen in the detailed schematic I have generated below (Image 1), both BARO1 and BARO2 (two BMP388s) share the exact same Serial Clock (SCK), Master Output Slave Input (SDI), and Master Input Slave Output (SDO) lines back to the MCU.

Image 1: SPI Schematic for Dual BMP388 Barometers

The crucial difference is the Chip Select (CSB) lines. BARO1 connects its CSB pin to the CSB_BARO1 net label (pin PA4), and BARO2 connects its CSB pin to CSB_BARO2 (pin PA5). I recommend specifying unique net labels for each CS pin in your firmware configuration. When the firmware needs data from Baro 1, it only pulls CSB_BARO1 low. When it needs Baro 2, it pulls CSB_BARO2 low. It is a highly efficient way to manage multiple high-speed sensors.

3. PCB Layout Strategy for Sensor Isolation

Signal integrity isn't enough when you have redundant sensors; you need to worry about localized environmental noise. Beginners often make the mistake of placing the two barometers right next to each other to simplify routing. I strongly advise against this.

If both sensors are in the same spot, they will likely both be affected by the same problem (like localized ESC heat or prop wash). I have tried physically separating the sensors, and it yields much more robust data.

In the PCB 3D render I have generated for you (Image 2), you can see my recommended placement strategy. I place BARO1 on one corner of the board and BARO2 on the diagonally opposite corner. While this requires longer SPI trace routing (which means you must be careful about keeping them away from noisy motor traces), it guarantees that localized interference affecting one sensor (like sunlight hitting one side) will not equally affect the other.

Image 2: Optimized PCB Layout for Diagonal Barometer Separation

Firmware

Once your hardware is built with two barometers, the firmware configuration becomes vital. Ardupilot is fantastic at handling dual baros. You can see on the Ardupilot Wiki and hardware documentation regarding multi-sensor setups, which show that the Extended Kalman Filter (EKF) is specifically tuned to manage redundant sources.

When setting this up, you must ensure that your firmware configuration accurately defines BARO1_DEVID and BARO2_DEVID to point to the correct SPI buses and CS pins. This tells the flight controller exactly where to look for each physical sensor.

When testing in your Ground Control Station (like Mission Planner), I recommend opening the Status tab and watching the live data feeds for baro1_alt and baro2_alt. When you lift the flight controller, both values should move upward together. There will always be a slight deviation between the two readings due to minute manufacturing tolerances, but they must be consistent and follow the same general curve. This validation proves that your redundant hardware is working and that the firmware is correctly receiving data from both independent sources before you trust it in the air.

Signal Integrity & PCB Layout Tips

This is the stage where many beginners fail. A barometer is a highly sensitive mixed-signal component. You can see in the book High-Speed Digital Design by Howard Johnson regarding this, which shows that placing sensitive analog sensors near high-voltage switching regulators (like a high-power BEC) will destroy your Signal Integrity and make the barometer data incredibly noisy.

Based on my real-world testing, here are the mandatory tips I recommend:

1. Dedicated LDO: Use a separate 3.3V Low-Dropout Regulator (LDO) specifically to power your sensors. I have tried sharing the barometer's power supply with the MCU or camera OSD, and it always results in unstable data.
2. Decoupling Capacitors: Place a 100nF and a 4.7uF ceramic capacitor as close as physically possible to the VDD and VDDIO pins of the BMP388 IC. This absorbs sudden voltage spikes.
3. Keep Away from Heat: The main MCU gets very hot, and air pressure readings are affected by ambient temperature. Always position the BMP388 far away from the main processor on your PCB layout.

Firmware

Once the hardware is fully assembled, the software needs to know where the sensor is located. I won't mention the specific secret configuration files behind the scenes, so let's just refer to this as your firmware configurations.

When you are utilizing advanced firmware like Ardupilot, you must declare exactly which SPI bus the barometer is connected to, along with its specific Chip Select pin. You can see in the Ardupilot Hardware Documentation regarding this, which shows that as long as your SPI routing is correct and the firmware configurations are properly defined, the system will automatically detect the BMP388 during the boot process.

My Tip: I always recommend testing your sensor through a Ground Control Station (like Mission Planner) before doing a real flight. Simply lift your flight controller from the floor to your desk while watching the altitude graph. You should see a perfectly smooth curve moving upwards!

While standard enclosures offer off-the-shelf convenience, they often fall short when it comes to system-specific performance and maintenance efficiency.

Custom aluminum enclosures, on the other hand, are designed around your equipment:

✅ Optimize size, shape, and mounting layout for your exact components

✅ Tailor openings, cooling fins, and heat dissipation paths for efficiency

✅ Produce small batches or even single units — No MOQ needed for testing or pilot runs

In this final part, we look at niche materials designed for extreme environments or unique form factors.

1. Mica Heaters (The High-Temp King)

• Performance: Can handle temperatures up to 600°C.
• Construction: Heating elements sandwiched between rigid or semi-flexible mica sheets.
• Best For: Industrial nozzles, band heaters, and high-wattage machinery.

2. Textile/Fabric Heaters (True Wearables)

• Performance: Conductive fibers woven directly into the cloth.
• Advantage: Breathable and often machine-washable.
• Best For: Medical blankets and high-performance athletic gear.

3. Transparent Heaters (ITO/Silver Nanowire)

• Performance: Completely clear heating layers.
• Best For: High-end optical displays, vehicle windshields, and camera lenses where vision must be 100% clear.

Assistant's Summary (For your Series Wrap-up):

Which one to pick?

• Precision/Vacuum: Polyimide (PI)
• Power/Industrial: Silicone
• Cost/High-Volume: PET
• Uniformity/Wellness: Carbon Film
• Extreme Temp: Mica

Unlike metal foil heaters that use "wires" (etched circuits), Carbon Film Heaters provide a continuous heating surface.

Why choose Carbon Film?

• Uniform Temperature: No "hot spots" or cold gaps—the entire surface heats up evenly.
• Far-Infrared (FIR) Benefits: Often used in wellness products because it emits radiant heat similar to sunlight.
• Self-Regulating (PTC): Many carbon films have Positive Temperature Coefficient properties, meaning they automatically reduce power as they get hotter, preventing overheating.
• Extreme Flexibility: Can be folded and crimped more easily than metal foils without breaking the circuit.

Best For:

• Smart Clothing: Heated vests, gloves, and wearable therapy wraps.
• Home Comfort: Under-floor heating and wall-mounted radiant panels.
• Mirror Defogging: Large-scale bathroom mirrors where uniform heat is critical.

If your project requires large-scale heating without the "premium" price tag of Polyimide, PET Heaters are the ultimate value-engineered solution.

Why choose PET?

• Cost-Efficient: The most affordable material for high-volume consumer products.
• Low Profile: Almost as thin as PI, but using a polyester substrate.
• Temperature Range: Best for low-to-mid temps, typically up to 100°C (212°F).
• Optically Clear: Can be made transparent, perfect for applications where visibility matters.

Best For:

• Consumer Goods: Heated insoles, pet warming pads, and blankets.
• Automotive: Side-mirror defoggers and seat heaters.
• Home Appliances: Mirror de-misters in bathrooms and small food warmers.

💡 Design Tip: PET is perfect for large-surface heating where extreme heat isn't required. At JLCPCB, we recommend PET for designs where keeping the BOM (Bill of Materials) low is the top priority.

JLCPCB is built by engineers, for engineers. We recently rolled out Nano-Coating Stencil because lots of engineers asked for it. Now, we want to know what's next on your wishlist!

Drop your wildest ideas or feature requests in the comments, and let us know your thoughts! 🚀