Every number, and how much we trust it
The full engineering specification for the board inside every Seelie Card case. Each figure is marked so you can tell what has been checked against a datasheet or the CAD model, what is calculated, and what nobody can know until there is hardware on a bench.
V verifiedVerifiedE estimatedEstimatedTBC to confirm on hardwareTo confirm on hardware
At a glance
- Function
- E-paper display with NFC tap-to-share, Wi-Fi and Bluetooth LE
- Modes
- Desk nameplate · event badge · tap-to-share card
- Outer dimensions
- 104.6 × 69.6 × 11.1 mmV verified
- Mass, assembled
- ≈ 68 gE estimated
- Power
- 1S Li-Po, USB-C rechargeable
- Enclosure
- Two-part 3D print, M2 screws
Mechanical
PCB
- Outline
- 100.0 × 60.0 mmV verified
- Thickness
- 1.6 mmV verified
- Layers
- 2 (F.Cu, B.Cu)V verified
- Assembly
- Single-sided, all parts on B.CuV verified
- Mounting holes
- 4 × Ø2.2 mm NPTH for M2V verified
- Min track width
- 0.25 mm signal / 0.40 mm powerV verified
- Min clearance
- 0.20 mm (0.50 mm on HV class)V verified
- Via / drill
- 0.6 / 0.3 mmV verified
- Surface finish
- ENIG recommended
- Placements
- 59 across 27 line itemsV verified
Enclosure
- Outer
- 104.6 × 69.6 × 11.1 mmV verified
- Wall / floor
- 2.0 mmV verified
- PCB fit clearance
- 0.3 mm per sideV verified
- Split line
- z = +1.6 mm, tray below, cover aboveV verified
- Internal cavity
- 100.6 × 65.6 × 5.5 mm deepV verified
- Board support
- 4 × Ø4.5 mm bosses, Ø1.7 mm pilotsV verified
- Fasteners
- 4 × M2 self-tapping; nylon nearest the coil
- Tray
- 20 591 mm³ ≈ 25.5 g PLAV verified
- Cover
- 9 736 mm³ ≈ 12.1 g PLAV verified
- USB-C opening
- 12.6 × 6.2 mmV verified
104.6 mm is the 100 mm board plus 0.3 mm clearance and a 2.0 mm wall on each side. The 69.6 mm dimension, rather than 64.6, makes room for the ESP32 module’s antenna, which overhangs the board edge by 4.72 mm by design.
Stack-up
- Front cover, panel recessed
- 2.0 mm · +1.6 → +3.6
- PCB
- 1.6 mm · 0 → +1.6
- Battery + clearance
- 5.5 mm · 0 → −5.5
- Tray floor
- 2.0 mm · −5.5 → −7.5
- Total
- 11.1 mm
Display
- Part
- GDEM0266T71WT (Good Display)
- Technology
- E-paper, monochrome, bistable
- Controller
- SSD1680 (Solomon Systech)
- Diagonal
- 2.66 in
- Resolution
- 152 × 296 pxV verified
- Active area
- 30.704 × 60.088 mmV verified
- Outline
- 36.30 × 71.82 × 1.0 mmV verified
- Interface
- 4-wire SPI, BS1 strapped lowV verified
- Connector
- 24-pin 0.5 mm FPC, 14 mm tailV verified
- Typical operating current
- 4.5 mAV verified
- Peak refresh current
- 40 mA typ / 60 mA maxV verified
- Operating temperature
- Limited by the panelTBC to confirm on hardware
Bistable means the image costs nothing to hold: the panel draws power only while it changes. The active area sits 6.07 mm off centre along the long axis, away from the FPC, so the window in the case is placed to match rather than centred.
Wireless
MCU module
- Module
- ESP32-C3-MINI-1-N4, RF pre-certified
- Core
- 32-bit RISC-V, single core
- Flash
- 4 MB
- Wi-Fi
- 802.11 b/g/n, 2.4 GHz
- Bluetooth
- BLE 5
- USB
- Native USB (GPIO18/19), no UART bridge
NFC
- Tag IC
- NT3H2111W0FHKH (NXP NTAG I²C plus)
- Standard
- NFC Forum Type 2, 13.56 MHz
- Antenna
- PCB coil, 8 turns, 0.6 mm trace, 0.3 mm gapV verified
- Coil area
- 15 × 50 mmV verified
- Coil inductance
- ≈ 1.93 µHE estimated
- Tuning capacitor
- 22 pF C0G/NP0V verified
- Field detect
- FD → GPIO3, deep-sleep wakeV verified
- Read range
- Measured after assembly; C14 is the tuning pointTBC to confirm on hardware
Power
Battery
- Chemistry
- Lithium polymer, 1 cell
- Capacity
- 500 mAh (200–600 mAh supported)
- Nominal / max
- 3.7 V / 4.2 V
- Cell
- Uxney 503035, 35 × 30 × 5 mm, protected
- Connector
- JST-PH 2.0 mm horizontal SMTV verified
- Retention
- Printed rib frame, 0.5 mm clearanceV verified
Polarity is not standardised on JST-PH plugs. Check it with a multimeter against J2 before the first connection.
Charging · MCP73871
- Input
- USB-C VBUS, 5 V
- Regulation voltage
- 4.20 VV verified
- Input current limit
- 500 mAV verified
- Charge current
- ≈ 303 mAE estimated
- Termination current
- ≈ 42 mAE estimated
- Safety timer
- 6 hV verified
- Low-battery threshold
- 3.1 VV verified
- Topology
- Power path: runs from USB when present
The pack has no accessible thermistor, so THERM is tied to VSS through a fixed 10 kΩ (0.5 V, between the cold and hot fault thresholds). Temperature protection is left to the pack’s own circuit.
Regulation and gauge
- Regulator
- AP2112K-3.3, 3.3 V, 600 mA minV verified
- Input source
- Charger SYS/OUT rail, not the battery terminal
- Fuel gauge
- MAX17048 ModelGauge, no sense resistor
- Gauge current
- 3 µAV verified
- Alert
- ALRT → GPIO4, deep-sleep wakeV verified
Current budget
- Deep sleep
- ≈ 10–20 µAE estimated
- Holding an image
- 0 µA (bistable)
- Display refresh
- 40–60 mA for a few secondsE estimated
- Wi-Fi transmit
- Up to ~350 mA peakE estimated
- NFC tap
- Field-powered, no MCU wake needed
Battery life is deliberately not quoted. It depends on how often the screen refreshes and how much the radio runs, so it will be measured on hardware rather than predicted.
Manufacturing
- Fabricator
- JLCPCB
- Process
- 2-layer, full SMT, single-sided
- Design rules
- Within standard capability, no fine-feature surcharge
- DRC
- 0 violations, 12 documented exclusionsV verified
- ERC
- Clean apart from one intentional noteV verified
- BOM
- 27 line items, 59 placements, LCSC parts throughoutV verified
- Enclosure
- FDM, PLA, 2 parts, no supports neededTBC to confirm on hardware
Still open
Known unknowns, published rather than hidden. Each one gets measured when the first boards arrive.
- The FPC tail has 0.07 mm of margin. Dry-fit before committing to a print.
- Connector clearances rest on datasheet figures; J1, J2 and J3 have no 3D models.
- The 0.3 mm case fit clearance is untested on a real print.
- NFC read range is unmeasured; C14 is the accessible tuning point.
- The board has not been fabricated yet.