Build Guide: Birdhouse Mesh Repeater

Solar-powered LoRa mesh repeater in a 3D-printed birdhouse enclosure — with the Inhero MR2. Electronics and antenna entirely in the roof space; the nesting chamber stays free.

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1. Stealth vs. Nesting-Friendliness

If the birdhouse is printed in black filament, the solar modules almost disappear visually. What is good for camouflage can end fatally for nesting birds. A black enclosure heats up strongly in the summer sun. Unlike a tree cavity, a thin plastic wall has practically no thermal mass — the inside temperature follows the sun immediately. For a brood, that would be critical. The MR2 has a temperature sensor – you can and should keep an eye on the inside temperature of the birdhouse via telemetry. When using black filament, please permanently close the entrance hole from the inside or fill the nesting chamber with rot-proof filler material to prevent nesting.

Note on hole diameter (birdhouse variant): Ø 30 mm suits blue tits, coal tits, marsh tits and similar small tits. Great tits prefer 32 mm, tree sparrows and pied flycatchers 34–35 mm.

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2. The Concept

The box consists of three printed parts:

• Base (120 × 120 × 150 mm, wall thickness 5 mm): the actual nesting box. Entrance hole Ø 30 mm in the front wall. Inside, along the front wall, runs the cable duct for the front solar module — it also serves as a climbing aid for the young birds (see box below).
  
  
• Intermediate floor: completely separates the nesting chamber from the technology compartment above and carries the MR2 with the battery pack. No cable, no electronics in the nesting chamber. Slides into the roof.
  
  
• Roof: carries the integrated groundplane antenna (868 MHz) with four radials in guide grooves and the radiator through the ridge, plus both 1 W roof solar modules. It is placed onto the base and secured with the mounting wire for tree installation.

Climbing aid: The vertical cable duct on the inside of the front wall plus the horizontal print layers of the inner wall give young birds grip when fledging. The inner walls remain untreated — do not sand, do not coat.

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3. Parts List

3.1 From the Shop (included in the kit)

Pos.	Component	Qty
1	MR2 solar mesh repeater board	1
2	U.FL retaining clip, ready-printed (PETG) — included with every MR2	1
3	Solar module 1 W	3
4	Solar connector board	1
5	Adapter cable for the solar connector board	1
6	MR2 battery cable with protection module — choose variant: LiFePO4 or Li-ion	1
7	Antenna kit: 5 × brass tubes Ø 2 mm, cut to length (1 × radiator 86 mm, 4 × radials 71 mm), SMA bulkhead socket	1
8	BLE adhesive antenna 2.4 GHz, U.FL	1
9	Pigtail SMA → U.FL	1
10	Mounting screws stainless steel A2, Ø 2.5 × 4.5 mm, T8 (MR2 mounting)	4

3.2 To Source Separately (not in the kit)

Component	Qty	Note
18650 cells, LiFePO4 or Li-ion — matching the chosen protection module variant!	5	Recommendation: cells with pre-welded solder tags (U/Z tags) — then a soldering iron is enough, no spot welder needed. The cell capacity will be needed later during configuration (section 7).
Alternatively: bare cells + spot welder	5	Never solder directly onto the cell can.
Filament		Color depending on variant (section 1). Make sure it is weather- and UV-resistant
Adhesive/sealant for the solar modules: WEICON Flex+bond, 85 ml, transparent — available in the shop	1	MS polymer — permanently elastic (compensates the different thermal expansion of panel and enclosure), UV- and weather-resistant, seals the cable pass-throughs at the same time. Also used to seal the antenna pass-through from below (assembly, step 3).
Small parts	—	Binding wire, spiral wrap, Kapton tape, fabric tape

3.3 Tools

Soldering iron, side cutters, TX8 screwdriver, multimeter for matching cell voltages, spot welder only for bare cells.

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4. Printed Parts

STL/3MF files: free download in the shop · also on MakerWorld — there with a ready-made Bambu print profile (supports & fuzzy skin already configured)

Print settings: Material of your choice — make sure it is weather- and UV-resistant. Supports: enable automatic supports — the model has some overhangs.

4.1 Painted-On Supports

Additionally, set painted-on supports in fill mode at the upper edges of the solar module cutouts: the automatic detection does not reliably catch these small overhangs, and without clean upper edges the modules will not fit properly into the cutouts later:

4.2 Fuzzy Skin (optional)

Fuzzy skin on the outer surfaces of base and roof — takes longer, but looks considerably higher-quality and masks the typical 3D-print look. Apply via painting/fill mode to the outer surfaces only:

Generator mode Displacement, noise type Classic, point distance 0.8 mm, thickness 0.3 mm, do not apply to the first layer

4.3 Positioning and Sliced Overview

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5. Preparation: Building the Battery Pack

Use only undamaged brand-name cells. The cell chemistry must match the ordered protection module variant (LiFePO4 ↔ LiFePO4, Li-ion ↔ Li-ion). The battery protection module is a mandatory component, not an accessory. Mind the polarity. Never solder directly onto the cell can. Before connecting cells in parallel, bring all cells to the same voltage — maximum 10 mV difference (multimeter!). If cells with different voltages are connected, high equalizing currents flow instantly — quite literally: sparks fly.

1. Connect 5 cells in parallel to form the pack — cells with solder tags → solder the tags. Alternatively: spot-weld bare cells. Use the battery compartment in the intermediate floor as a spacer. First minus, then flip the pack, then plus.
2. Connect the battery cable with the protection module
3. Insulate the pack, attach the protection module to the right outer cell so that it fits into the battery compartment. Fix with Kapton tape.
4. Slide the battery pack into the compartment, insulate the plus side with fabric tape or similar.

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6. Assembly

The antenna is a λ/4 groundplane for 868 MHz, fully integrated into the roof: radiator 86 mm through the ridge, four radials of 71 mm each in the guide grooves. Work through the following steps in this order:

1. Remove the ground pins of the SMA socket (side cutters).
   
2. Solder the radiator: solder the longer tube (86 mm) onto the center pin of the socket.
   
   
3. Drill out the antenna hole in the roof with a 2 mm drill, push the radiator through. While the solder joint is still hot, it fuses with the plastic of the roof. Then seal the pass-through from below with Flex+bond.
   
   
4. Insert the radials into the grooves from below and align them
   
   
5. Solder the radials
   
   
6. Thread the front solar module's cable through the pass-through, glue the module in place with Flex+bond
   
   
   
7. Glue the roof solar modules in place, screw the pigtail onto the groundplane. Hold the SMA socket in place with needle-nose pliers while doing so
   
   
8. Mount the battery pack (align the protection module with the groove provided for it), stick on the BLE antenna, mount the MR2 with the supplied screws
   
   Caution: switch off the MR2 with the DIP switch before connecting the battery — otherwise risk of damage to the LoRa TX. Mind the inverted switch logic: switch position “On” activates “3.3V off” (as printed on the silkscreen) — the board is then off.
   
   
9. Wire the solar modules to the solar connector board and the MR2, connect the LoRa pigtail. Route the cables between the USB socket and the RAK. Then fit the U.FL retaining clip (included with the MR2) over the RAK module: it secures the U.FL connections — otherwise the antenna connector can pop off unnoticed when sliding roof and intermediate floor together.
   
   
10. Slide the intermediate floor with MR2 and battery into the roof, thread the front panel cable through the pass-through and connect it to the solar connector board. Slide together — done
    
    

Antenna tuning: The supplied tube lengths were measured in the assembled roof and tuned to the 868 MHz band.

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7. Configuring the MR2

Firmware: The MR2 ships without application firmware (OTAFIX bootloader only). Flashing is most convenient after step 9 and before sliding everything together (step 10), while USB-C is still freely accessible — the antenna is already connected at that point. That is exactly what matters: the LoRa antenna must be connected, because after flashing, depending on the firmware version, transmission by the repeater cannot be ruled out. The board must also be switched on, otherwise flashing does not work — switch position “Off”, because of the inverted logic from step 8. Then: press the reset button twice in quick succession (double reset), the board mounts as a USB drive, copy the .uf2 file via drag and drop. Ready-made, tested MeshCore builds for the MR2 are available in the firmware releases on GitHub.

To configure, connect via the MeshCore app using the admin access. The screenshot shows the values for five LiFePO4 cells of 2200 mAh and three 1 W modules:

• set board.bat lifepo1s — cell chemistry 1S LiFePO4; defines the charge-termination, sleep and protection thresholds. With a Li-ion pack, set the matching Li-ion chemistry instead; the available values are listed in the CLI reference.
• set board.batcap 10000 — always set the battery capacity to match the cells actually fitted, following the 90% rule: cell capacity × number of cells × 0.9. Here, five LiFePO4 cells of 2200 mAh = 11,000 mAh, of which 90% ≈ 10,000 mAh. With five Li-ion cells of 3500 mAh, the calculation is 5 × 3500 = 17,500 mAh × 0.9 ≈ 15,750 mAh. The deduction makes the SOC display and the runtime prediction conservative — when 10% is shown, at least 10% really is in the battery (FAQ #4).
• set board.imax 500 — maximum charge current. The rule of thumb is panel power ÷ battery voltage, but what counts is the input power actually achievable: the three modules deliberately face different directions and never face the sun at the same time — so the nominal sum of 3 W never arrives together. A value set too high makes the panel voltage collapse in weak light and the charger stops (FAQ #5).
• set board.fmax 20% — frost protection: around the freezing point (approx. +3 to −2 °C) the charge current is limited to 20% of imax; below that, charging is fully blocked for LiFePO4 by chemistry. The repeater keeps running on solar regardless — only charging is limited (FAQ #6).
• set board.mppt 1 — enable MPPT.
• set board.leds 0 — board LEDs off: they save power and are invisible inside the closed box anyway.

Check: get board.conf shows all configured values at a glance, get board.selftest probes the onboard components. Then fully charge the battery once (e.g. via USB-C): the coulomb counter needs one full charge as its 100% reference — until then, the SOC shows “N/A”. From now on the MR2 also delivers the telemetry that lets you watch the inside temperature of the box — particularly important with a black enclosure (section 1).

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8. Location & Tree Mounting

Nesting box rules and solar requirements go well together:

• Orientation: Entrance hole facing east/southeast — not towards the weather side (west), not permanently in blazing southern sun. The solar modules on three sides ensure that the orientation can be chosen according to the birds' needs. Especially in winter, when the roof is covered in snow, the vertical south module delivers the highest yield.
  
• Mounting: Thread binding wire through the holes in the base; the roof can be secured with the wire through a hole in the guide rails of the intermediate floor
• Radio: A compromise between height and shading — every meter of height adds range. Too high in the tree crown, on the other hand, creates solar/LoRa shading again.
  
• Energy: The MR2 is extremely frugal (1 Wh/day). Together with the 5×18650 cells and the 3 W of solar, the repeater keeps running at sites where other setups fail. Should the battery ever run empty due to insufficient solar yield, the Inhero MR2 goes into deep sleep and wakes up on its own once the sun has sufficiently recharged the battery.

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9. Legal & Safety

• The kit contains tested, compliant individual components (MR2: CE/RED). Final assembly is carried out by the buyer at their own responsibility for personal use.
• This guide was written to the best of our knowledge but does not replace expertise. Handling lithium cells requires care: the instructions in section 5 — matching cell voltages before connecting in parallel, protection module, insulation — are mandatory. Building this project is at your own risk; no liability is accepted for damage resulting from improper assembly or unsuitable components, to the extent permitted by law.
• Operation in the 868 MHz band in accordance with the applicable regulations (duty cycle); the MR2 enforces these in firmware.
  

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© Inhero GmbH · shop.inhero.de · Enclosure design (STL/3MF files) licensed under CC BY-NC-SA 4.0 — private reprinting and further development expressly welcome · Version 1.2