Linux Cyberdeck Design

flux

There’s still a moderate amount left before this is a full manufacturable board. The first-pass schematic is started, but we are not ready for PCB layout/manufacturing yet.
Main things still left to figure out
  1. Display connection
    • Exact Waveshare 6.25" DSI LCD-B connector pinout
    • DSI lane count
    • Backlight power/current
    • Touch interface, if any
    • Correct FPC connector part
  2. Battery and power
    • Exact 10,000 mAh battery pack
    • Battery connector/current rating
    • Battery protection/NTC details
    • Confirm charger settings for that pack
    • Validate 5 V boost converter can handle CM5 + LTE + display + USB-A peaks
  3. Protection parts
    • USB-C ESD protection
    • USB-A USB 3.0 ESD protection
    • HDMI ESD protection
    • SIM card ESD protection
    • Possibly battery/input fuse or protection
  4. Regulator final values
    • Final inductor part numbers
    • Capacitor voltage/package choices
    • TPS61288 compensation check
    • Thermal/current margin check
    • Layout-sensitive switching-node constraints
  5. CM5 details
    • Decide whether to add RTC backup for CM5 VBAT
    • Decide whether to expose nRPIBOOT/service pads
    • Confirm GPIO assignments for LTE, audio, IMU, keyboard wake
  6. LTE/SIM7600 details
    • Confirm exact SIM7600G-H-M.2 hardware guide handling for VDD_AUX and VDD_1V8
    • Confirm LTE/GNSS antenna connector placement strategy
    • Add SIM ESD
    • Add RF/layout keepout rules
  7. Keyboard board
    • Main-board FPC is planned, but keyboard PCB itself still needs to be designed
    • Need switch/keycap sourcing
    • Need keyboard RP2040 schematic/firmware pin map finalized
  8. Mechanical basics
    • Rough board size
    • Port locations
    • Battery location
    • Screen/keyboard placement constraints
    • Mounting holes
    • Antenna placement/keepouts
  9. PCB layout setup
    • Stackup choice, likely 6-layer because of USB 3.0, HDMI, MIPI DSI, RF, and power density
    • Controlled-impedance rules
    • Differential-pair rules
    • Power trace/current rules
    • Thermal copper areas
  10. Bring-up and manufacturing prep
  • Test pads
  • Debug headers
  • Board bring-up checklist
  • BOM cleanup
  • Footprint review
  • DRC
  • Gerbers/BOM/pick-and-place
My estimate
Schematic is roughly 55–65% figured out.
Full board readiness is more like 30–40% complete, because layout, power validation, protection, display details, and mechanical constraints are still significant.
The biggest blockers are:
  1. Exact display connector/pinout
  2. Exact battery pack
  3. Power validation for the 5 V rail
  4. ESD/protection parts
  5. Mechanical board size/port placement
  6. Keyboard PCB design
Once those are decided, the remaining work becomes much more straightforward.
Power, display, protection
Find display pinout
Validate power rail
Add protection parts
Add test pads
Review battery connector

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Schematic

Layout

3D View

Project Specification — Linux Cyberdeck
Project Overview
Status: Draft / architecture review required before schematic capture. Updated direction: Raspberry Pi Compute Module 5 carrier, tablet-style battery, custom keyboard PCB based on M5Stack CardKB proportions, and Waveshare 6.25inch DSI LCD (B) as the display candidate.
A portable Linux cyberdeck built around a Raspberry Pi Compute Module 5 carrier board with LTE/GNSS connectivity, LoRa, USB-C PD charging plus USB 2.0 gadget/rpiboot data, USB-A 3.0 host, HDMI, a Waveshare DSI display, split custom keyboard PCB, microSD storage, mono speaker, and compact clamshell battery power.
Intended Use
  • Portable Linux computer / cyberdeck prototype.
  • User-facing compute, networking, radio, display, keyboard, audio, and battery operation.
  • Current stage: requirements capture and architecture selection; schematic capture should not begin until the compute module, screen/keyboard interface, and battery architecture are confirmed.
What the Device Should Do
  • Boot and run Linux on Raspberry Pi Compute Module 5.
  • Use selected CM5 SKU SC1598 / CM5108000: 8 GB RAM, Lite / 0 GB eMMC, wireless.
  • Support LTE Cat-4 cellular data and GNSS using a SIM7600G-H-M.2 module.
  • Support LoRa using an RP2040-LoRa development board with SX1262.
  • Provide one USB-C port for power and data.
  • Provide one USB-A 3.0 host port.
  • Provide one HDMI port.
  • Connect to the specified screen/keyboard assembly.
  • Drive a small speaker.
  • Operate from a battery connection and support charging/power-path behavior.
Main Features

Table

FeatureBaseline DirectionStatus
Main computeRaspberry Pi CM5 SC1598 / CM5108000, 8 GB RAM, Lite / 0 GB eMMC, wirelessSelected
Cellular/GNSSSIM7600G-H-M.2 over USB 2.0, with SIM socket and antennasFeasible, needs exact carrier details
LoRaWaveshare RP2040-LoRa daughterboard, preferably as pluggable moduleFeasible, band decision needed
USB-CPD sink/UFP charging plus USB 2.0 device/gadget/rpiboot dataConfirmed
USB-AUSB 3.0 host portFeasible if compute platform exposes USB 3.x host
HDMIExternal HDMI connector and/or internal display feedBlocking decision
DisplayWaveshare 6.25inch DSI LCD (B), 720 x 1560, MIPI DSI + I2C touchCandidate selected; SOM compatibility must be checked
Keyboard2-layer keyboard PCB, 60-key tactile/keycap matrix, RP2040 + QMK, USB HID over FPCConfirmed
StoragemicroSD card slot connected to CM5 Lite SDIO storage interfaceDirection selected
AudioI2S or USB audio to small class-D speaker amplifierNeeds compute platform interface and speaker spec
Battery2S Li-ion or USB-C PD power-bank style architecture recommendedUser decision needed
System Architecture
Recommended baseline: design a custom carrier around Raspberry Pi Compute Module 5. CM5 already includes the processor, LPDDR4x, PMIC sequencing, boot-critical hardware, and Raspberry Pi software support. The carrier handles battery power, USB, LTE/GNSS M.2, LoRa, display, keyboard, audio, and external connectors.
Diagram



  
    
  
  
    
  


































Battery Pack
Charger / Power Path
USB-C Power/Data
5V System Rail
3.8V LTE Rail
3.3V Control/RF Rail
RK3588-class SOM or SBC
SIM7600G-H-M.2 LTE/GNSS
RP2040-LoRa SX1262 Board
Optional USB Hub
Keyboard / Touch USB
USB-A 3.0 Host
HDMI Connector
Internal Display Interface TBD
Class-D Speaker Amp
Small Speaker
Hardware Subsystems
Compute
  • Selected direction: Raspberry Pi Compute Module 5 carrier board.
  • CM5 variants support 2 GB, 4 GB, 8 GB, and 16 GB LPDDR4x; use 8 GB minimum.
  • Selected CM5 is Lite / 0 GB eMMC, so the carrier will provide a microSD card slot for boot/storage.
  • Selected CM5 is wireless-capable, so enclosure antenna clearance or external antenna strategy must be handled.
  • CM5 main input is 5 V and the carrier power system must support CM5 peak current plus display, USB, LTE, speaker, and battery charging loads.
Cellular / GNSS
  • Target module: SIM7600G-H-M.2 / SIM7600X-H-M2 family.
  • Supply range found: 3.3–4.2 V.
  • Power rail must support approximately 2 A-class transmit bursts with large low-ESR bulk capacitance near the module.
  • Host interface is USB 2.0; route as 90 ohm differential pair.
  • Needs SIM/eSIM decision, cellular antenna, diversity antenna decision, GNSS antenna decision, RF keepouts, and regulatory review.
LoRa
  • Target board appears to be Waveshare RP2040-LoRa with SX1262.
  • Board size found: 21 mm x 41 mm.
  • Frequency options:
    • LF: 410–525 MHz.
    • HF: 850–930 MHz.
  • Antenna connector: onboard IPEX with included IPEX-to-SMA adapter cable.
  • Interface to Linux host should be decided: USB, UART, or a carrier-level debug/programming path.
Display
  • Candidate: Waveshare 6.25inch DSI LCD (B), 720 x 1560 IPS capacitive touch display.
  • Interface: Raspberry Pi-style 2-lane MIPI DSI plus I2C touch.
  • Power: 5 V panel power plus 3.3 V/I2C side signals per Waveshare pinout.
  • Advantage: documented for Raspberry Pi DSI overlays, making CM5 a better match than an arbitrary RK3588 SOM.
  • Verify exact CM5 DSI connector mapping/cable orientation before schematic capture.
Keyboard
  • Reference: M5Stack Unit CardKB / CardKB v1.1.
  • Reference interface: I2C at address 0x5F over HY2.0-4P/Grove-style connector with GND, 5 V, SDA, SCL.
  • Reference size: approximately 84–88 mm x 54 mm x 5 mm depending revision.
  • User direction: design a custom keyboard PCB slightly longer than CardKB.
  • Recommended implementation: direct-wired keyboard matrix on the main board, scanned by a small onboard keyboard MCU, exposed to CM5 as USB HID with optional wake/power sideband GPIO.
USB
  • USB-C role is currently ambiguous and must be defined before schematic capture.
  • USB-A 3.0 requires a compute platform with USB 3.x host capability and controlled-impedance routing.
  • Internal peripherals may exceed available host ports; likely need a USB 2.0 hub for LTE, keyboard/touch, LoRa, and debug if these are USB.
HDMI
  • External HDMI is feasible but requires 100 ohm differential routing, ESD protection, DDC, hot-plug detect, connector shield strategy, and 5 V HDMI power.
  • If the internal screen also needs HDMI, the compute platform must support multiple display outputs or the design must choose between internal display and external HDMI.
Audio
  • Small speaker path should use a dedicated class-D amplifier.
  • Interface depends on compute platform: I2S preferred if exposed; USB audio is fallback.
  • Speaker impedance and power target are needed.
Interfaces and Connections

Table

InterfaceProposed Electrical PathNotes
USB-CUSB-C connector + CC/PD controller + ESD + power pathRole TBD
USB-A 3.0RK/SOM USB 3.x host to USB-A connector85 ohm SuperSpeed pairs
HDMIRK/SOM HDMI output to HDMI connector100 ohm diff pairs
LTE modemUSB 2.0 host/hub to M.2 module90 ohm USB pair; 3.8 V burst rail
SIMSIM7600 module USIM pins to SIM socket/eSIMAdd ESD near SIM socket
GNSS/LTE RF50 ohm RF paths to antennas/connectorsAntenna plan required
LoRaUSB/UART to RP2040-LoRa daughterboardBand and connector TBD
SpeakerI2S/USB audio to class-D ampSpeaker spec TBD
Screen/keyboardTBD: likely USB-C/USB/HDMI-style external cablePinout unknown
Power and Runtime Expectations
  • Battery direction: compact communicator/tablet-style Li-ion/LiPo pouch pack.
  • Recommended chemistry is now 1S Li-ion/LiPo for thin mechanical packaging, with high-current boost conversion to the 5 V system rail.
  • Confirmed battery pack: 1S2P using 2x BatterySpace PL-5467100-2C cells with Tenergy 32190 PCM, 8500 mAh / ~31.5 Wh nominal.
  • Use USB-C PD charging with a 1S switching charger/power-path, I2C fuel gauge, NTC monitoring, and run-while-charging support.
  • Include fuel gauge, pack protection, power button/soft-shutdown, and low-battery cutoff.
Preliminary Power Tree and Power Budget
Detailed preliminary assumptions are tracked in the separate Power Budget file.
High-level rails:

Table

RailLoads
Main battery / USB-C PD inputCharger, power path, system regulators
5 V systemRK3588 SOM/SBC input, USB-A VBUS, display/keyboard if 5 V, USB hub
3.8 V LTESIM7600G-H-M.2 burst supply
3.3 V logicRP2040-LoRa, level shifters, control, low-speed peripherals
Audio railSpeaker amplifier, if not powered from 5 V
Backlight/display railTBD after display documentation
Manufacturing and Assembly Expectations
  • If using SOM/SBC: custom carrier board likely 6 layers minimum due USB 3.0, HDMI, LTE USB, RF, and power integrity.
  • If raw RK3588S2 + LPDDR4x is chosen: expect 8+ layer HDI/microvia design, controlled impedance, DDR simulation/validation, and substantially higher cost/risk.
  • RF antennas and M.2 connector placement must be considered with the enclosure, display metalwork, and battery location.
Firmware-Relevant Hardware Requirements
  • Linux BSP support depends on selected RK3588S2/SOM/SBC vendor.
  • Need serial console/debug access.
  • LTE should be exposed to Linux as USB modem interface; support ModemManager/NetworkManager where possible.
  • RP2040-LoRa requires firmware update/programming path.
  • Keyboard/display drivers depend on the actual interface of the screen/keyboard assembly.
Physical Design Expectations
  • Keyboard assembly likely dominates product size; candidate AKP846 dimensions found around 371 x 219 x 21 mm.
  • Need exact enclosure size, mounting hole locations, connector exits, battery location, antenna locations, speaker port, cooling path, and SIM access.
  • RK3588-class SoC needs heat spreader or conduction path.
Important Design Decisions
  1. Use SOM/SBC for compute rather than raw RK3588S2 + LPDDR4x for the first prototype.
  2. Treat SIM7600G-H-M.2 as a high-burst-current RF module requiring a dedicated 3.8 V-class supply and RF-aware layout.
  3. Treat the RP2040-LoRa board as a daughterboard unless the user wants to integrate the LoRa circuit directly.
  4. Do not design display/keyboard connector circuitry until the exact interface is documented.
  5. Use at least a 6-layer carrier PCB for the high-speed/RF carrier approach.
Assumptions
  • Prototype-first design, not immediate production certification.
  • Linux runs on a purchased RK3588S2/RK3588-class module/SBC.
  • Cellular modem is USB-connected.
  • LoRa board can be connected as a daughterboard.
  • Screen/keyboard assembly is used as a purchased module rather than reverse-engineered internally.
  • Battery is rechargeable Li-ion/LiPo with charging from USB-C.
Open Decisions / Questions for User
  1. Keyboard final layout drawing: 60-key legend, Fn map, tact/keycap part selection.
  2. Enclosure CAD kickoff: hinge, SMA bulkhead locations, antenna keepouts, service hatch.
  3. RJ45 Ethernet is omitted.
  4. Should the custom keyboard enumerate as USB HID, I2C, or both?
  5. What keyboard switch/key technology and approximate size should be used?
  6. USB-C role is confirmed as PD sink/UFP charge plus USB 2.0 data, not USB 3.0 and not full dual-role/source.
  7. Is HDMI for external output only, or should the internal DSI display and external HDMI work simultaneously?
  8. Which LoRa frequency band is required: 433/470, 868, or 915 MHz?
  9. Do you want internal antennas or external SMA connectors for LTE/GNSS/LoRa?
  10. What speaker impedance/power target and enclosure size/shape should be used?
Change Notes
  • Initial specification created from user requirements.
  • Project renamed to Linux Cyberdeck.
  • Architecture risk review added: raw RK3588S2 + LPDDR4x is not recommended for the first prototype.
  • Updated per user direction: switched from RK3588-class SOM carrier to Raspberry Pi Compute Module 5 carrier using attached CM5 datasheet, retaining tablet-style battery, M5Stack CardKB as keyboard size/interface reference, custom keyboard PCB, and Waveshare 6.25inch DSI LCD (B) display candidate.
  • Updated per user direction: selected DigiKey SC1598 / CM5108000 CM5 Lite wireless 8 GB module, USB-C charging+data, microSD instead of NVMe, and direct-wired custom keyboard via onboard keyboard MCU.
  • Updated per confirmed decisions attachment: USB-C data is USB 2.0 gadget/rpiboot, battery is 1S2P 8500 mAh verified pack, keyboard is split RP2040/QMK PCB, and only keyboard layout plus enclosure CAD kickoff remain open.

  • Project Overview

  • Intended Use

  • What the Device Should Do

  • Main Features

  • System Architecture

  • Hardware Subsystems

  • Compute

  • Cellular / GNSS

  • LoRa

  • Display

  • Keyboard

  • USB

  • HDMI

  • Audio

  • Interfaces and Connections

  • Power and Runtime Expectations

  • Preliminary Power Tree and Power Budget

  • Manufacturing and Assembly Expectations

  • Firmware-Relevant Hardware Requirements

  • Physical Design Expectations

  • Important Design Decisions

  • Assumptions

  • Open Decisions / Questions for User

  • Change Notes