Our own circuit boards, in the classroom whiteboard

Boards we design for the smart whiteboard, with every chip soldered on them: the RK3576J processor and its memory, two room camera chips, the 96-LED time bar, the Wi-Fi module, the mic, the speaker amp, the security chip, a CO2 chip and the tap-in reader. One rigid-flex piece lies in the header rail behind the opal cover; a small air board sits in the side frame at the height the California rule asks for, and a tray board under the pen tray lid, both on one latched bus. No bought modules, ribbons or adapters; only 5 V in the board.

Stage 1 of 6 done: shape and placementNot yet ready to manufactureUpdated 4 November 2026 · rev A-0

Design files Design review Quote pack Who can make it Our board platform

The board in 3D

Every part at its real size, in its real place. Turn it, zoom in, switch between the boards in the whiteboard and laid flat, and click any part to see what it is. The chip bodies are simple blocks until each part's own 3D model is added.

Show the whiteboard

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Drag to turn · scroll to zoom · right-drag to move · click a partDrag to turn · tap a part

Where everything is in the whiteboard

Room camerasheader rail

Two bare Sony IMX415 camera chips on small tabs off the main board, each under an M12 lens that passes through the header cover to just inside its face, turned 30° out and 20° down: every desk, the back corners, the group table and the door. They count heads, never faces, and keep no picture.

Time barbehind the cover

A long light strip stands just behind the opal cover with 96 colour LEDs in one row: the lesson timer running down green, amber and red, the reading-group colours, and the register and air calls.

Processor, radio and securityheader rail

The RK3576J with its memory on the main board, a heat block into the aluminium rail, the Wi-Fi module behind the opal, the security chip that signs every call, the latched microSD card with our software, and a tamper sensor held by a magnet in the cover.

Mic and speakerrail floor

A MEMS mic on a small tab over the rail’s mic port hears the sound level and the fire-alarm tone only, never words; the speaker amp drives the speaker over the floor grille.

CO2left side frame

A small air board in the side-frame pocket, 4.5 ft up as the California rule asks, carries the CO2 chip behind the vent slots: it calls ‘open the window’.

Tap-inpen tray

A tray board under the tray lid with an NFC chip and a printed coil, where pupils tap their cards for the register check. It hangs on the same latched bus as the air board, down the side frame.

The whiteboard boards laid flat, both sides, every part at its real size

Laid flat: the mic tab on its tail, the main board with the camera tabs in front and the light strip above on F1; then the inlet tab, the air board and the tray board. Tap the drawing to open it full size.

Design review: checked before we order

Every board-level number ClassOne's jobs depend on, checked against its target with the source of each number, using the rules every one of our boards shares (products/_shared/board-rules.mjs). Fixed means a lesson changed this board; to prove means it passes on paper and is measured on rev A before boards are ordered.

No check fails16 pass · 3 fixed by the review · 12 to prove before we order · 0 failDesign review of 4 November 2026

Area	Check	Our board	Target	Status
Camera	Left room camera: a pupil's head (150 mm) at the back seat at 7.58 m M12 lens, 102° across: about 37.6 px per degree across 3840 px. The person counter is trained on heads from about 20 px (est.); it counts heads, never faces, and keeps no picture.	42.7 px	≥ 20 px	passes
Camera	Left room camera: frame rate the calls need A standard mode of the IMX415.	1 fps at 3840 × 2160	chip: 30 fps at 3840 × 2160	passes
Camera	Left room camera: data rate vs its 4-lane link 98 % spare on the link.	0.08 Gbps (10-bit)	≤ 80 % of 3.564 Gbps	passes
Camera	Right room camera: a pupil's head (150 mm) at the back seat at 7.58 m M12 lens, 102° across: about 37.6 px per degree across 3840 px. The person counter is trained on heads from about 20 px (est.); it counts heads, never faces, and keeps no picture.	42.7 px	≥ 20 px	passes
Camera	Right room camera: frame rate the calls need A standard mode of the IMX415.	1 fps at 3840 × 2160	chip: 30 fps at 3840 × 2160	passes
Camera	Right room camera: data rate vs its 4-lane link 98 % spare on the link.	0.08 Gbps (10-bit)	≤ 80 % of 3.564 Gbps	passes
Camera	Image processor load, all cameras 2 cameras into one image processor.	17 Mpx/s	≤ 480 Mpx/s (RK3576J ISP)	passes
Camera	AI engine time per frame One person counter (int8) on the two 8 MP views, merged; the mic level and the CO2 are read by the CPU. Measured on the dev kit.	6 TOPS	a head count from both views in under 2 s every 10 s, the group-table check at the same time	to prove on the dev kit
Power	Supply About 5 W counting (RK3576J 3 W, two cameras 0.6 W, Wi-Fi 0.5 W, CO2, tap-in and mic 0.4 W), the time bar capped at 4 W by its 1 A limit and the firmware, 1.5 W speaker peaks (est.): 10.5 W, 70 % of the adapter.	a listed USB-C adapter giving 5 V 3 A (SELV) at the wall socket beside the board, into the inlet tab at the rail's right end	≤ 70 % of the adapter (15 W)	passes
Power	Power cut Pulling the adapter mid-count is part of the rev A tests.	no cells: a power cut stops the board; the register log is written to eMMC on every change and signed	no lost register or air log in a power cut	to prove on the dev kit
Heat	RK3576J temperature, a sunny classroom in June (30 °C) with the heating or the sun on the wall The header rail sits near the ceiling, where the room is warmest; counted at 40 °C inside. 3 W through a 24 × 24 aluminium block and gap pads to the 2.4 m aluminium header rail (4 K/W, est.).	52 °C	≤ 85 °C (rated)	passes
Heat	Camera chips away from the processor A warm sensor adds noise to dim winter mornings.	left camera 157 mm, right camera 61 mm from the RK3576J	≥ 30 mm	passes
Shock	Shock and vibration A foam ball thrown at the board in wet play, about 20 J on the cover (est.); the boards are on stand-offs in the rail, 2 m up. MEMS clocks are fitted anyway, and the card socket is latched.	50 g (est.)	standard parts	passes
Software	Starts our software from the microSD card, no setup Owner requirement: power it from its own supply and our software runs from the card. Rev A and sale boards boot from the card; the eMMC holds no system copy (it ships empty, so the card always starts first: Rockchip tries the eMMC before the card) and keeps the day log. Updates write to the card with two system copies, only after school hours and never during a lesson. The quote asks for U-Boot and a device tree from Rockchip's RK3576 SDK.	microSD socket with a hinged, latched lid (Amphenol 101-00660 class), fitted on every board: our software starts from the card	card socket fitted on every board, latched	passes
Software	Card power switch and protection A card that hangs must be restarted by cutting its power, not the whole board; the card slot is the one place a person touches the electronics (lesson: sdstart). Change: U90, U91 added (4 Nov 2026, CricketOne card-start review).	1 power switch and 1 ESD array for 1 card socket	every socket: switched card supply, ESD on all 6 lines	fixed by the review
Software	The card wins the start Rockchip's start order is SPI flash, eMMC, card, USB: a written eMMC starts before the card. Proved on the dev kit: power on with a card in and the eMMC empty (lesson: sdstart). Change: eMMC ships empty and the loader reads the card first (4 Nov 2026; it used to say the eMMC kept a copy, which would have started instead of the card).	eMMC shipped empty; our loader reads the card first	the processor starts from the card every time	fixed by the review
Software	Card grade Consumer cards wear out and fail hot; the image is read-only with a separate data partition. Proved: 1,000 power cuts during writes on rev A (lesson: sdstart).	industrial pSLC microSD (Kingston Industrial or Swissbit S-56u), −40 to 85 °C	rated for the heat, cold and writes	to prove on the dev kit
Software	Clip buffer for an unsure call The rest of the memory holds Linux, the program and the AI model (lesson: clip).	98.8 s of 8-bit 1 fps video in 40 % of the 2 GB memory	≥ 3 s	passes
Radio	Wi-Fi from inside an aluminium header rail The rail is aluminium on three sides; only the opal front lets radio out, so the antenna sits right behind it. Measured on rev A (lesson: antenna).	Wi-Fi 6 module on the light strip, its chip antenna 4 mm behind the opal cover, between the rail's top and bottom lips	certified Wi-Fi module, the school's WPA3-Enterprise Wi-Fi	to prove on the dev kit
Layout	Fast lines on a solid ground plane The layout rules go to the maker in the quote; the routed board's design rule check (0 copper errors, every keep-out kept) and the maker's impedance coupon prove them (lesson: planes).	RK3576J memory; 2 camera MIPI links (100 Ω pairs); USB (90 Ω); antenna feed (50 Ω, keep-out on every layer); card lines (length-matched, no vias under the socket)	ground on inner layer 1, supply on inner layer 2, no vias in pads, impedance lines routed first	to prove on the dev kit
Moisture	Conformal coating Board wipes and cleaning spray reach the tray and the cover every day; all six boards get the same coat. Asked for in the quote (lesson: moisture).	coated	coated, sensors, sockets and antennas masked	passes
Fit	Board inside the product CAD, every part checked in 3D The board is checked on its own; the rev T CAD run places it in the product and checks every part in 3D (lesson: fit3d).	not yet in the product CAD	nothing touches	to prove on the dev kit
Camera	Every head-count, room-clear and group call in a camera view Every inView target from the CAD (front and back desks on each side, the centre, the back corners, the group table, the door) from the lens front's real place in the cover.	Left room camera: worst 30.7° / 21.7°; Right room camera: worst 43.6° / 21.7°	inside the 102 × 69.6° view	passes
Camera	Camera windows in the header cover The bench windows were 30 × 30 round the Camera Module boards. Our lens passes through the cover to 0.5 mm inside its face, but the line of sight to a door at the front corner runs 80° from the cover, so the far side of the lens rim needs the window to open outward (lesson: window). Both windows open outward, because the door can be on either side of a real classroom. Change: CAD rev T: camera windows 30 × 30 → 63 × 34, opening outward (4 Nov 2026).	left view reaches 17.5 mm out from its axis, right 41.6 mm (the door, 80° from the cover); margins 6.7 and 1.5 mm	rev T windows 63 × 34, x ±42 to ±105	fixed by the review
Fit	Camera tabs on their brackets Each tab hangs off the main board's front edge and is held on its camera's axis by a printed bracket clipped to the rail floor; the brackets go in the rev T CAD and are checked in 3D there (lesson: fit3d).	Left room camera: holder 0.3 mm behind the cover, barrel 6 mm, hinge 22.9 mm, lowest corner 2026.5 mm; Right room camera: holder 0.3 mm behind the cover, barrel 6 mm, hinge 22.9 mm, lowest corner 2026.5 mm	holder ≥ 0.3 mm off the cover, hinge within the 25 mm flex, clear of the rail floor and the light strip	to prove on the dev kit
Light	Time bar behind the opal cover The bench used 12 bought LED sticks; on our strip the LEDs sit in one row. The evenness through the opal and the brightness at the back seat are checked on rev A.	96 RGB LEDs at 6.4 mm pitch across the 614 mm bar, 4 mm behind the cover; 1 A limit	one even bar seen from the back of the room; never glaring	to prove on the dev kit
Sensors	CO2 chip where the California rule puts it The bench SCD30 module (±60 ppm at 1,000 ppm) is replaced by the SCD43 chip soldered on our air board; its accuracy is taken from Sensirion's datasheet (est. ±(30 ppm + 3 %), to read) and checked against a reference meter on rev A.	Sensirion SCD43 in the left side-frame pocket, 1,388 mm (4.5 ft) up, behind the vent slots	3 to 6 ft up, 5 ft from doors and windows (PUC 1625); ±75 ppm at 1,000 ppm	to prove on the dev kit
Sensors	Tap-in through the tray lid The bench PN532 module sat under the same lid; the coil is tuned on rev A with the lid and the aluminium tray round it.	NXP PN7160 with a 40 × 35 printed coil 3 mm under the 3 mm PETG lid	an NTAG215 card read at 20 mm or more, every tap	to prove on the dev kit
Fit	Leads and the bus The CO2 chip must sit 3 to 6 ft up and the tap-in at a child's reach, 1.2 m below the header, so the air and tray boards hang on one latched, keyed bus in the side frame's channel; the inlet is at the rail's end beside the wall socket.	L1 about 1.08 m of 18 AWG, 0.1 V drop at 2.1 A; L2 + L3 about 2.46 m of 26 AWG, 0.27 V drop at the tray	L1 ≤ 0.15 V; tray ≥ 3.8 V for its 3.3 V supply; differential I²C ≤ 3 m (est.)	passes
Security	Cover and tray-lid tamper sensors The bench used a plunger switch pressed by the cover; on our board a Hall switch needs no boss. The magnet pockets go in the rev T CAD and the switch point is measured on rev A.	DRV5032 Hall switches 4 mm behind the header cover and under the tray lid, each held by a Ø6 × 3 magnet bonded in the cover or lid	cover or lid opened = logged and signed	to prove on the dev kit
Fit	Flex lengths F1 carries the time-bar data and the Wi-Fi module's SDIO; the flex maker confirms the SDIO impedance over that length.	F1 61 mm up to the light strip; mic tail 163 mm along the rail floor	routed and held in the rev T CAD	to prove on the dev kit

Before we order the first boards, we prove these on the RV1126B development kit or in the rev A tests:

AI engine time per frame
Power cut
Card grade
Wi-Fi from inside an aluminium header rail
Fast lines on a solid ground plane
Board inside the product CAD, every part checked in 3D
Camera tabs on their brackets
Time bar behind the opal cover
CO2 chip where the California rule puts it
Tap-in through the tray lid
Cover and tray-lid tamper sensors
Flex lengths

Where the design stands

1Shape and placementdone
Main board, camera tabs, light strip, mic tab, inlet tab, air board and tray board in the whiteboard’s shape, all 144 parts placed at their real size, every room call checked from where each lens sits, and KiCad design rule check (0 violations).
2Schematicnext
Every wire between the chips, from the V2 core and C1 camera circuits.
3Footprintsnext
The exact solder pads under each chip.
4Routinglater
Copper tracks on all layers, along the long light strip and the flexes.
5Files for the makerlater
Gerbers with copper, drill, mask, paste, the rigid-flex drawing, the lead drawings and the assembly parts list. These go to the board maker.
6Rev A boardsMar 2027
Made, assembled and tested on our fixture.

Design files (rev A-0)

These are the stage 1 files: the board's shape and where every part goes. A board maker needs the stage 5 files to build it.

All files (zip)Everything below in one download, with the quote and review KiCad boardclassone-board.kicad_pcb: open with KiCad 10 (free)3D model (STEP)The bare boards for mechanical CAD Side A drawing (PDF)Down to the rail floor, out to the cover, up to the tray lid Side B drawing (PDF)Up into the rail Parts and placement (CSV)Every part, its size, side and position

Who can make it

The whiteboard set is an 8-layer rigid-flex piece with a 640 mm light strip, plus three small boards and three leads made to length. It needs a maker who builds rigid-flex boards with long panels and fine-pitch ball-grid chips. We plan three quotes once the stage 5 files are ready: two from China for price, and one from the US for speed.

Maker	Where	Rigid-flex	HDI / layers	Assembly	Fit for us
PCBWayfirst quote	Shenzhen, China	yes, 6 to 16 layers	HDI up to 32 layers, 0.35 mm BGA pitch	yes, turnkey, incl. BGA and X-ray	Best fit for rev A: the rigid-flex board and its assembly in one order
NextPCBsecond quote	Shenzhen, China	yes	HDI, 6 to 32 layers	yes (PCBA)	Second quote, to compare price and lead time
ALLPCB	China (a network of partner factories)	yes, through partner factories	1 to 30 layers	yes	Third quote; check which factory builds it
JLCPCB	Shenzhen, China	no (flex only: 1, 2 and 4 layers, up to 490 mm)	HDI added Sep 2026	yes, incl. BGA	Not for the one-piece board today. Good for the test fixture, simple boards, and the fallback of separate rigid boards joined by soldered flex
Sierra Circuits (ProtoExpress)US quote	Sunnyvale, California, USA	yes	yes	yes, in-house, incl. BGA; turnkey in about 5 days	US option: fastest turn and engineering help, at a higher price
Cirexx	Santa Clara, California, USA	yes	yes	yes (turnkey or consigned)	Second US option
Advanced Circuits	Aurora, Colorado, USA	yes	check	yes	US quick-turn; check its rigid-flex assembly
Epec	New Bedford, Massachusetts, USA	yes	check	yes; also builds battery packs	US option that can also make a certified LiFePO4 pack

From each maker's own capability pages, checked 3 November 2026. Limits change, so each quote confirms them for our exact stack-up.

Full design notes

All 144 parts, what is on each board, every connection, heat, power, the factory test, cost and timeline.

ClassOne: circuit boards of our own

What changed (4 Nov 2026). The rev A bench whiteboard is built from bought boards joined by leads: a Raspberry Pi 5, two Camera Module 3 Wide boards on ribbons, an SPH0645 mic board, 12 NeoPixel sticks, a MAX98357A amp board, an ATECC608 board, an SCD30 CO2 module up the side frame and a PN532 board in the pen tray. ClassOne now gets boards of our own, like CricketOne, DockOne and StudyOne, with every chip placed straight onto them, made with every shared design-review rule from the start.

The chips: the V2 core (Rockchip RK3576J, 2 GB LPDDR4X, 16 GB eMMC, AMPAK AP6275S Wi-Fi 6/BT module), two bare Sony IMX415 8 MP camera chips under M12 lens holders (the C1 camera on the board), 96 RGB LEDs for the time bar, an Infineon IM69D130 MEMS mic, the MAX98357A speaker amp, the security chip, Hall tamper switches, a Sensirion SCD43 CO2 chip and an NXP PN7160 NFC chip with a printed coil.
The shape: the whiteboard’s electronics live in four places, so the boards do too. In the header rail, one rigid-flex piece: an 8-layer main board (220 × 34 mm) flat on the rail floor behind the camera windows; two 16 × 16 mm camera tabs on 25 mm flex hinges off its front edge, each held on its camera’s axis by a printed bracket; a 4-layer light strip (640 × 27 mm) standing 4 mm behind the opal cover on a 16 mm flex; a small mic tab on a tail over the rail’s mic port. At the rail’s right end, an inlet tab with the USB-C power inlet. In the left side frame’s pocket, 4.5 ft up, an air board with the CO2 chip. Under the pen tray’s lid, a tray board where pupils tap in.
Why more than one board: the CO2 chip must sit 3 to 6 ft up (California PUC 1625) and the tap-in at a child’s reach, 1.2 m below the header; no board can span that. The air and tray boards hang on one latched, keyed bus (differential I²C) in the side frame’s cable channel, like the lead between DockOne’s two guards. The inlet is at the rail’s end, beside the wall socket.
Only 5 V in the board. Power comes from a listed USB-C adapter (5 V 3 A) at the wall socket beside the board. No cells: a classroom has power whenever school is open.
Made from the shared rules: MEMS clocks, the latched microSD card with our software on every board, conformal coating against daily board wipes, the antenna checked for the aluminium rail on rev A, cameras 30 mm or more from the processor, the lens chosen from the calls and its front just inside the cover (lesson: window).

The bench whiteboard stays the test rig until the boards arrive.

1. The shape: six boards, one bus

Piece	Size	Layers	Where	What
Main board	220 × 34 mm, 1.6 mm	8	flat in the header rail, side A 10 mm over the aluminium rail floor	the V2 core, card, security, amp, camera supplies, power and bus headers
Camera tabs (2)	16 × 16 mm, 0.8 mm, on 25 mm flex hinges	8	off the main board’s front edge at x ±60, turned 30° out and 20° down	IMX415 and M12 lens holder each, lens front 0.5 mm inside the cover’s face
Light strip	640 × 27 mm, 1.6 mm	4	standing 4 mm behind the opal cover, above the camera windows, on a 16 mm flex (F1, 61 mm)	96 time-bar LEDs, Wi-Fi/BT module, cover tamper switch
Mic tab	14 × 16 mm, 0.8 mm, on a 6 mm tail (163 mm)	2	on the rail floor over the mic port at x −250	IM69D130 mic and its gasket
Inlet tab	34 × 34 mm, 1.6 mm	4	at the rail’s right end, the USB-C mouth in the end-wall hole	USB-C inlet, eFuse, latched power header
Air board	24 × 38 mm, 1.6 mm	2	standing in the CO2 pocket in the left side frame, 1,362 to 1,400 mm up	SCD43 CO2 chip, bus buffer, 3.3 V, two latched bus headers
Tray board	200 × 39 mm, 1.6 mm	4	flat 3 mm under the tray lid in the NFC compartment	PN7160 NFC chip and printed coil, bus buffer, 3.3 V, tray tamper switch

Leads: L1 (inlet tab to main board, 5 V, about 1.1 m of 18 AWG, Molex Micro-Fit 3.0 2-pin latched); L2 (main board to air board, about 1.8 m) and L3 (air board to tray board, about 0.7 m), both 26 AWG with JST GH 6-pin latched ends, in the side frame’s channel.

2. What is on the boards

Main board, side A (down, to the rail floor): RK3576J (U1) with a 24 × 24 aluminium heat block and gap pads to the rail floor (HS1), LPDDR4X (U2), eMMC (U11).

Main board, side B (up): the RK3576J decoupling field (C1), RK806S power (U3), 24 MHz and 32 kHz MEMS oscillators (Y1, Y2), ATECC608B (U8) and the ID chip (U9), the latched microSD socket (J1), reached by taking off the header cover, the eFuse (U42), the latched power header (J2) and bus header (J3), the PCA9615 bus buffer (U43), the MAX98357A amp (U31) and the speaker wire pads (PD1, the 28 mm speaker stays over the floor grille), the two cameras’ supplies (U21, U22), factory pads (TP1).

Camera tabs: an IMX415 (U200, U210) under an M12 lens holder with a 102° × 69.6° lens (LH1, LH2) on each, turned 30° out and 20° down; head counts only, never faces.

Light strip, side A (to the cover): 96 WS2812B-class LEDs at 6.4 mm pitch (D1–D96: the time bar running green to amber to red, group colours, register and air calls), the AP6275S Wi-Fi/BT module (U5) with its antenna keep-out (ANT1) behind the opal, the DRV5032 cover tamper switch (U7) under a magnet in the cover. Side B: the level shifter (U36) and the time bar’s power and 1 A limit (U37).

Mic tab: IM69D130 (MK1) over a hole through the tab, the gasket (GK1) to the rail’s mic port.

Inlet tab: the USB-C power-only receptacle (J4) in the end-wall hole, the eFuse and TVS (U40), the latched power header (J5).

Air board: Sensirion SCD43 (U50) behind the vent slots, the PCA9615 (U51), a 3.3 V LDO (U52), the two bus headers (J50, J51).

Tray board: the printed 40 × 35 mm coil (ANT2) on side A under the tap-here mark; PN7160 (U60), its matching network (U61), the PCA9615 (U62, end of the bus), a 3.3 V LDO (U63), the bus header (J60) and the DRV5032 tray-lid tamper switch (U64) on side B.

3. Every connection, checked

Link	How	Checked against
Camera chips to RK3576J	4-lane MIPI CSI-2 each, across the 25 mm flex hinges	IMX415 data sheet: 891 Mbps per lane; at 1 fps each uses 0.08 Gbps of 3.56
Time bar	one data line up F1, 3.3 → 5 V level shifter	WS2812B data sheet
Wi-Fi/BT	SDIO and UART up F1	AMPAK AP6275S (RK3576 SDK default)
Mic	PDM along the mic tail	Infineon IM69D130 data sheet
Speaker amp	I2S on the main board, the speaker’s own wires to the pads	MAX98357A data sheet
CO2 and tap-in	I²C through PCA9615 differential buffers over L2 and L3 (about 2.5 m in all)	NXP PCA9615 data sheet (est. 3 m at 400 kHz, to read); PN7160 and SCD43 on I²C
Power in	USB-C, 5.1 kΩ CC pull-downs, 5 V up to 3 A, eFuse at 3.5 A; L1 drops 0.1 V at 2.1 A	USB Type-C spec 2.x (power-only sink); the adapter is listed
Card	SD bus to the RK3576J, latched socket	Amphenol 101-00660 family drawing

Every mating pair is checked against the makers’ documents, never “same as” another board.

4. Heat

The 2.4 m aluminium header rail is the heat sink: about 3 W from the RK3576J goes through the heat block into the rail floor (4 K/W est.), so the chip sits near 52 °C with the rail at 40 °C inside near a warm ceiling. The camera chips are 61 mm and 157 mm from the processor.

5. Power budget (est.)

State	Draw
Counting every 10 s (RK3576J, two cameras at 1 fps, Wi-Fi)	4.1 W
CO2, tap-in, mic, security	0.4 W
Time bar (1 A limit, firmware caps the brightness)	up to 4 W
Speaker peak (a chime or a group call)	1.5 W
Peak	10.5 W, 70 % of the 15 W adapter
Night: CO2 and tamper only, processor asleep	0.6 W

6. Factory test (every board, every time)

Spring-pin fixture on TP1 and the small boards’ pads: 5 V in through the USB-C, the eFuse trip at 3.5 A, every rail, boot from the card, a frame of a test chart from each camera, all 96 LEDs, the mic against a 1 kHz tone, the amp into a test speaker, the CO2 chip against fresh air (about 420 ppm), a test card read through a 3 mm lid, both tamper switches with a magnet, the security chip’s key, the Wi-Fi link. Each board gets its serial number in the ID chip.

7. Who makes what

One maker makes the rigid-flex piece and the three small boards and assembles them (turnkey), and makes the three leads to length. We supply the microSD cards with our software and the lenses focused at 4 m (est.). The quote pack is /build/classone-quote.

8. Cost per whiteboard, electronics (est.)

Item	Cost
V2 core (RK3576J, LPDDR4X, eMMC, power, AP6275S)	$42
Two IMX415 camera chips, holders and lenses	$28
SCD43 CO2 chip	$20
PN7160, coil match, mic, amp, security, ID, buffers	$10
96 LEDs and their power	$8
USB-C, eFuses, socket, Hall switches, passives	$6
Boards (8-layer rigid-flex with a 640 mm strip, three small boards), 1,000 whiteboards	$30
Three leads	$5
Assembly and test	$12
microSD card with our software	$4
Total	about $165 per whiteboard (est.)

The bench whiteboard’s bought boards cost about $300 at qty 1 (Pi 5, two cameras, SCD30, PN532, 12 LED sticks and the small boards), so our boards are about $135 cheaper per whiteboard at 1,000 (est.).

9. Timeline

Step	When
Shape and placement (this page)	done, 4 Nov 2026
Rev T CAD: the boards in the whiteboard CAD, every part checked in 3D; the camera windows already opened outward	next
Schematic, footprints, routing	Dec 2026 – Jan 2027
Rev A boards made and tested	Mar 2027 (est.)

10. Still to check

The rev T CAD changes still to draw: the camera brackets on the rail floor, magnet pockets in the header cover and the tray lid, the side frame’s cable channel from the rail to the pocket and on to the tray.
The SCD43’s accuracy from Sensirion’s data sheet against California’s ±75 ppm at 1,000 ppm (est. ±(30 ppm + 3 %)), and a reference-meter check on rev A.
The PN7160 coil tuned with the 3 mm lid and the aluminium tray round it.
Wi-Fi range from inside the aluminium rail (antenna behind the opal).
The 640 mm light strip’s panel length and the F1 SDIO impedance with the maker.

Sources

Rockchip RK3576 brief: https://www.rock-chips.com/a/en/products/RK35_Series/2024/0524/1977.html
Sony IMX415 (8.46 MP, 4-lane MIPI): https://www.sony-semicon.com/en/products/is/security/security.html
AMPAK AP6275S: https://www.ampak.com.tw/
Sensirion SCD4x CO2 sensors: https://sensirion.com/products/catalog/SCD43
NXP PN7160: https://www.nxp.com/products/PN7160
NXP PCA9615 differential I²C buffer: https://www.nxp.com/products/PCA9615
Infineon IM69D130: https://www.infineon.com/cms/en/product/sensor/mems-microphones/mems-microphones-for-consumer/im69d130/
Analog Devices MAX98357A: https://www.analog.com/en/products/max98357a.html
Microchip ATECC608B: https://www.microchip.com/en-us/product/atecc608b
TI DRV5032: https://www.ti.com/product/DRV5032
California PUC 1625 (CO2 monitors in classrooms): https://www.cpuc.ca.gov/
The whiteboard: products/classone/cad/classone-cad.mjs (rev A, camera windows rev T); the boards: products/classone/hardware/pcb/classone-board.mjs

Design review (4 Nov 2026)

Every board is checked by the same rules (products/_shared/board-rules.mjs), one for each lesson any of our boards has taught us. ClassOne’s boards were made with every rule from the start: 16 pass, 3 fixed, 12 to prove, 0 fail. The full review, with every number and its source, is on the board page. It shows:

Room camera pixels: a pupil’s head at the back seat (7.6 m) fills about 43 px against a 20 px need; at one frame a second each 8 MP chip uses 2 % of its link, and both together 17 Mpx/s of the image processor’s 480.
Every room call in view: front and back desks on both sides, the centre, the back corners, the reading-group table and the door, from where each lens really sits in the cover.
The camera windows open outward (fixed): the line of sight to a door at the front corner runs 80° from the cover, so the far side of the lens rim needs room; both windows grow from 30 × 30 to 63 × 34, opening outward, because the door can be on either side of a real classroom (lesson: window). Drawn in the CAD the same day.
The latched microSD (J1) is fitted, and our software starts from it; updates run only after school hours.
Conformal coating against board wipes and spray is asked for in the quote.
Fast lines on a solid ground plane (to prove, lesson: planes, from the CricketOne test-board layout of 4 Nov 2026): RK3576J memory; 2 camera MIPI links (100 Ω pairs); USB (90 Ω); antenna feed (50 Ω, keep-out on every layer); card lines (length-matched, no vias under the socket). Ground on the layer next to the parts (inner layer 1, supply on inner layer 2; the whole bottom of a 2-layer section), one via beside each ground and supply pad and none in pads, no copper or vias in the antenna keep-out on any layer or under the card socket, the impedance lines routed first with a test coupon. The quote asks for it; the routed board’s design rule check proves it.
To prove on rev A: the AI time per count, Wi-Fi from inside the rail, the camera brackets, the time bar through the opal, the CO2 chip’s accuracy, the tap-in read range, the tamper magnets, the flexes, and the boards in the rev T CAD.

The request for quote is /build/classone-quote.