Our own circuit boards, in the crossing's signal head

Boards we design for the smart crossing signal, with every chip soldered on them: the RK3576J processor and its memory, the approach and crossing camera chips, the kerb radar chip, LTE-M with a soldered eSIM, the call lights, the security chip, and on its own board the supply, the lamp-feed sensors, the controller contacts and a backup cell. They line the walls of the same 356 × 254 × 1,067 mm signal head behind its own LED modules, which stay the controller's; flexes join them, and one latched lead carries 5 V from the power board. No plugs, ribbons or adapters inside.

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 signal head 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 head

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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 signal head

Approach cameradoor corner

A bare Sony IMX415 camera chip under a 102° M12 lens on a tab behind the door’s solid bottom road-side corner, below the green module, 25° down the approach: every vehicle and cyclist coming, the queue, counts, class and speed.

Crossing cameraroad-side wall

A second IMX415 behind a 56 × 28 window in the road-side wall, 25° down: the stop line, both lanes of the crossing and the far kerb, for red-light running, people still crossing, near misses and a blocked crossing.

Kerb radarback wall

A TI IWRL6432AOP 60 GHz radar chip with its antennas on the package, 30° down behind the back-wall radome: people waiting at the kerb and a slow walker still in the near lane, in rain, fog and the dark.

Call lights and toneback wall and floor

Eight white LEDs behind the “seen you” slot and eight red behind the officers’ confirmation slot, and a buzzer over the tone holes in the floor. The head’s own red, amber and green modules stay the controller’s.

Processor and radiosfloor and back

The RK3576J with its memory flat on the head floor, a heat block to an aluminium spreader bolted to the steel pole bracket; LTE-M with a soldered eSIM and BLE for the fit-up phone, their antennas at the far side of the head from the pole.

Supply, lamp feeds and contactsleft wall

An unswitched 120 V feed into a class II 5 V supply on its own board; current sensors the head’s own lamp wires pass through unbroken, so the controller still sees a dead red module; three isolated contacts on the controller’s own detector inputs; one soldered 18650 cell that keeps the fault log going through a power cut.

The signal-head boards laid flat, both sides, every part at its real size

Laid flat: the power board on the left; the main board with the back strip above it (F2), the side strip to its right (F3) and the corner board below (F1, drawn short); the three sensor tabs on the right. Tap the drawing to open it full size.

Design review: checked before we order

Every board-level number RoadOne's calls 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 · 5 fixed by the review · 12 to prove before we order · 0 failDesign review of 4 November 2026

Area	Check	Our board	Target	Status
Camera	Approach camera: a car (1.8 m wide) 60 m out on the approach at 59.35 m M12 lens, 102° across: about 37.6 px per degree across 3840 px. Counts, class and speed need about 30 px across a car (est.); speed comes from many frames as the car closes, so 10 fps is plenty.	65.4 px	≥ 30 px	passes
Camera	Approach camera: frame rate the calls need A standard mode of the IMX415.	10 fps at 3840 × 2160	chip: 30 fps at 3840 × 2160	passes
Camera	Approach camera: data rate vs its 4-lane link 77 % spare on the link.	0.83 Gbps (10-bit)	≤ 80 % of 3.564 Gbps	passes
Camera	Crossing camera: a person (0.45 m wide) reaching the far kerb at 8.68 m M12 lens, 102° across: about 37.6 px per degree across 3840 px. The person model finds people from about 20 px across (est.); walkers move slowly, so 10 fps is plenty for near misses and a blocked crossing.	111.8 px	≥ 20 px	passes
Camera	Crossing camera: frame rate the calls need A standard mode of the IMX415.	10 fps at 3840 × 2160	chip: 30 fps at 3840 × 2160	passes
Camera	Crossing camera: data rate vs its 4-lane link 77 % spare on the link.	0.83 Gbps (10-bit)	≤ 80 % of 3.564 Gbps	passes
Camera	Image processor load, all cameras 2 cameras into one image processor.	166 Mpx/s	≤ 480 Mpx/s (RK3576J ISP)	passes
Camera	AI engine time per frame One vehicle and person model (int8) on both 8 MP views at 10 fps; the radar's people tracks and the feed sensors are read by the CPU. Measured on the dev kit.	6 TOPS	a walk-demand or extension call in under 0.5 s; counts on every frame of both views	to prove on the dev kit
Power	Supply About 6.0 W by day (RK3576J 3.5 W, two cameras 0.6 W, radar 0.3 W, LTE-M 0.5 W, Wi-Fi/BT 0.3 W, call lights 0.3 W, the rest 0.5 W) and 7 W with the cell charging (est.): 35 % of the supply.	Mean Well IRM-20-5 PCB-mount 5 V 20 W supply (class II, listed) on an unswitched 120 V feed (a spare conductor of the head's own signal cable), on the power board	≤ 70 % of the supply (14 W)	passes
Power	Power cut Pulling the feed is part of the rev A tests; a thermistor holds charging outside 0 to 45 °C (lesson: charge), which matters in a head that bakes in summer sun.	one soldered 18650 cell (Samsung INR18650-35E) on the power board: in a power cut the crossing is dark, so the RK3576J sleeps and wakes every 60 s to log and send the fault over LTE-M, about 0.4 W, 26 h on the cell (est.)	the fault log and its message for 12 h in a power cut	to prove on the dev kit
Heat	RK3576J temperature, a summer afternoon (40 °C air) with sun on the dark polycarbonate head A closed signal head in full sun runs well above the air; counted at 60 °C inside (est., logged on rev A). 3.5 W through a 24 × 24 aluminium block and gap pads to a 3 mm aluminium L-spreader on the head floor, its upright bolted through the back wall to the steel pole bracket and the 114 mm steel pole (5 K/W, est.).	78 °C	≤ 85 °C (rated)	to prove on the dev kit
Heat	Camera and radar chips away from the processor A warm camera chip adds noise at night, when the crossing needs it most.	approach camera 216 mm, crossing camera 177 mm, kerb radar 146 mm	≥ 30 mm	passes
Shock	Shock and vibration A vehicle clipping the pole or a high load hitting the head shakes the boards; about 100 g at the boards on their stand-offs (est.); a head knocked off its pole is a fault call, not a design case. MEMS clocks are fitted anyway, and the card socket is latched.	100 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 counts and the call log. Updates write to the card with two system copies, only in the quiet hours the traffic centre sets, never while a call is placed; the controller keeps its own timings throughout. 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).	39.5 s of 8-bit 5 fps video in 40 % of the 4 GB memory	≥ 3 s	passes
Radio	LTE-M from the signal head The head is polycarbonate, but the steel pole and its bracket stand right behind the back wall; the antenna sits at the far side of the head from them. Measured on rev A (lesson: antenna).	BG95-M3 with a soldered eSIM, its chip antenna in the back strip's top-left corner behind the polycarbonate, 73 mm from the steel pole	certified module; calls, counts and faults reach the traffic centre	to prove on the dev kit
Radio	BLE for the contractor's fit-up phone Only fit-up and the zone check; everything else goes over LTE-M.	AP6275S on the back strip, antenna at its left edge, 93 mm from the pole	pairing from the footway, 5 m below (est.)	passes
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 Rain, road spray and condensation as the head cools at night reach the boards; all five boards and three tabs 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 crossing call in view Every inView target from the CAD (the first car waiting, the queue 20 m back, a vehicle 60 m out, a cyclist in the kerb lane, the opposing lane; a car over the stop line, people in both lanes and at the far kerb, a near miss, a car stopped on the studs; people waiting at and back from the kerb, stepping on and still in the near lane) from each lens or chip's real place in its wall.	Approach camera: worst 18.6° / 23°; Crossing camera: worst 19.5° / 23.4°; Kerb radar: worst 28.6° / 7°	inside each sensor's view	passes
Camera	Approach camera looks out of the door corner The bench head looked down through a window in its floor, but from there the count line 60 m up the approach lies 88° off the floor, so no floor window could show it (lesson: window). The door faces the approach; its bottom corner below the green module is solid polycarbonate, and the corner board stands 25 mm behind it. Change: CAD rev T: approach window moved from the floor to the door corner, 24 × 24 (4 Nov 2026).	window 24 × 24 in the door's solid bottom road-side corner, 22 mm clear of the green module; steepest line of sight 37° (margin 3.4 mm)	every line of sight under 82° from its wall	fixed by the review
Camera	Crossing and radar windows The round 18 mm crossing window was sized for the bench camera board; the car over the stop line lies 70° off the road-side wall, so the lens rim needs a long window along the road. The radar slot (50 × 20) grows to its chip's calls. Change: CAD rev T: crossing window Ø18 → 56 × 28; radar slot 50 × 20 → 54 × 24 (4 Nov 2026).	crossing window 56 × 28 (margin 0.2 mm, steepest 70°); radar radome 54 × 24 (margin 6.8 mm)	each view inside its window	fixed by the review
Safety	The controller's own lamp drive untouched The bench design took its supply from "the head's own feed", but a plain head has only the three switched lamp feeds. A supply on a lamp feed would add current that could hide a dead red module from the controller's lamp-out check. The power board now takes an unswitched 120 V feed on a spare conductor of the head's own signal cable, fused in the cabinet, and only senses the lamp feeds without touching them. Change: board B22: unswitched supply on a spare conductor, feed sensors through-window (4 Nov 2026).	three PCB current transformers with the head's own red, amber and green feed wires passing through unbroken; nothing of ours on the lamp feeds	the controller and its conflict monitor see exactly the plain head's load	fixed by the review
Safety	Controller contacts The highway authority's cabinet wiring rules decide whether detector pairs may share the signal cable; on rev A we follow the local rule, with a separate detector cable where it asks for one.	three photo-MOS contacts (5,000 V isolation, est.) and a spring-clamp terminal for the controller's own detector inputs, on spare conductors back to the cabinet	a detector call like any listed detector; the controller keeps its own minimums, maximums and safety timings	to prove on the dev kit
Safety	Supply kept on its own board The power board keeps the 120 V behind a printed shield on the left wall, away from the cameras and radios. Creepage is checked in the layout.	the unswitched feed into a spring-clamp terminal on the power board, fuse, varistor, IRM-20-5 (class II); only 5 V and the contact drive on lead L1	class II creepage on the power board; no 120 V on any other board	to prove on the dev kit
Fit	Sensor tabs on their brackets Each tab hangs off its board and is held on its sensor's axis by a printed bracket; the brackets go in the rev T CAD and are checked in 3D there (lesson: fit3d).	Approach camera: 0.3 mm inside the wall, hinge 14.5 mm; Crossing camera: 0.3 mm inside the wall, hinge 19.5 mm; Kerb radar: 0.3 mm inside the wall, hinge 25.5 mm	chip or holder ≥ 0.3 mm inside the wall, hinge within the 40 mm flex	to prove on the dev kit
Fit	Behind the head's own modules The controller's modules stay exactly as in a plain head, so a module swap by the maintenance crew never touches our boards.	every board behind the 100 mm module zone; the corner board in the door corner 22 mm clear of the green module	the head's own LED modules, visors and door unchanged	passes
Fit	Flexes and the lead F1 and F3 carry 4-lane camera links; the flex maker confirms the MIPI impedance over those lengths.	F1 274 mm to the corner board, F2 44 mm to the back strip, F3 131 mm to the side strip; L1 about 0.49 m of 20 AWG, 0.032 V drop	routed and held in the rev T CAD; L1 ≤ 0.15 V	to prove on the dev kit
Security	Door tamper sensor The bench used a plunger switch pressed by the door; the magnet boss goes in the rev T CAD and the switch point is measured on rev A.	DRV5032 Hall switch on the corner board, held by a Ø6 × 3 magnet on a printed boss on the door	door opened = logged and signed	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
RK3576J temperature, a summer afternoon (40 °C air) with sun on the dark polycarbonate head
Card grade
LTE-M from the signal head
Fast lines on a solid ground plane
Board inside the product CAD, every part checked in 3D
Controller contacts
Supply kept on its own board
Sensor tabs on their brackets
Flexes and the lead
Door tamper sensor

Where the design stands

1Shape and placementdone
Main board, corner board, back strip, side strip, three sensor tabs and the power board in the signal head’s shape, all 68 parts placed at their real size behind the head’s own modules, every view checked through its window in 3D and KiCad design rule check (0 violations).
2Schematicnext
Every wire between the chips, from the V2 core, C1 camera and power circuits.
3Footprintsnext
The exact solder pads under each chip.
4Routinglater
Copper tracks on all layers, the camera lanes over the flexes.
5Files for the makerlater
Gerbers with copper, drill, mask, paste, the rigid-flex drawing 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 boardroadone-board.kicad_pcb: open with KiCad 10 (free)3D model (STEP)The bare boards for mechanical CAD Side A drawing (PDF)Down to the floor, out to the door and the walls Side B drawing (PDF)Up and into the head Parts and placement (CSV)Every part, its size, side and position

Who can make it

The signal-head set is an 8-layer main board with three 4-layer boards and three tabs on flexes, plus a 2-layer power board. It needs a maker who builds rigid-flex boards with long flex arms 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 68 parts, what is on each piece, every connection, heat, power, the factory test, cost and timeline.

RoadOne: circuit boards of our own

What changed (4 Nov 2026). The rev A bench signal head is built from bought boards joined by leads: a Raspberry Pi 5, two Camera Module 3 Wide boards on ribbons, an HLK-LD2450 radar module, three clip-on current clamps and an ADS1115 board, an LSM6DSOX board, three relays, two NeoPixel sticks, a piezo, an ATECC608 board, a Walter LTE-M board, a PowerBoost with a LiPo and an IRM-20-5 on flying leads. RoadOne now gets boards of our own, like CricketOne and BayOne, with every chip placed straight onto them, made with every shared design-review rule from the start.

The chips: the V2 core (Rockchip RK3576J, 4 GB LPDDR4X, 32 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), a TI IWRL6432AOP 60 GHz radar chip with its antennas on the package, a Quectel BG95-M3 LTE-M module with a soldered eSIM, 16 call-light LEDs with two drivers, an SMD buzzer, an ST LSM6DSOX motion chip, the security chip and a Hall tamper switch; on the power board a Mean Well IRM-20-5 supply, three PCB current transformers on the lamp feeds with an ADS131M04 ADC, three photo-MOS controller contacts and one soldered 18650 backup cell with its charger and thermistor.
The shape: the head’s own three 300 mm LED modules fill the front 100 mm and stay exactly as they are, driven by the controller. Our boards line the walls behind them. An 8-layer main board (110 × 90 mm) lies flat on the head floor; a small 4-layer corner board stands behind the door’s solid bottom road-side corner, below the green module, with the approach camera; a 4-layer back strip stands inside the back wall with the kerb radar, the two call-light rows and the radios; a 4-layer side strip stands inside the road-side wall with the crossing camera; a 2-layer power board on the left wall keeps 120 V on its own. Flexes F1, F2 and F3 join the main board to the others; one latched lead joins the power board.
Two fixes in the same run:
- From a window in the head’s floor, the count line 60 m up the approach lies 88° off the floor, so no floor window could show it (lesson: window). The approach camera now looks out of the door’s bottom road-side corner, which faces the approach and is solid polycarbonate below the green module. The crossing window grew from a round 18 mm to 56 × 28, because the car over the stop line lies 70° off the road-side wall. Drawn in the CAD the same day (rev T).
- The bench design took its supply from “the head’s own feed”, but a plain head has only the three switched lamp feeds, and a supply on a lamp feed could hide a dead red module from the controller’s lamp-out check. The power board now takes an unswitched 120 V feed on a spare conductor of the head’s own signal cable (fused in the cabinet), and senses the lamp feeds with current transformers the wires pass through unbroken.
Made from the shared rules: MEMS clocks, the latched microSD card with our software on every board, conformal coating against rain and condensation, a thermistor on the backup cell, the antennas checked near the steel pole on rev A, cameras 30 mm or more from the processor, every line of sight under 82° from its wall.

The bench signal head stays the test rig until the boards arrive.

1. The shape: five boards, three tabs

Piece	Size	Layers	Where	What
Main board	110 × 90 mm, 1.6 mm	8	flat on the head floor, side A 10 mm over a 3 mm aluminium L-spreader	the V2 core, card, security, motion chip, buzzer, lead header
Corner board	44 × 44 mm, 1.6 mm, on F1 (274 mm)	4	standing 25 mm behind the door’s bottom road-side corner, 22 mm clear of the green module	approach camera tab, door tamper switch, supplies
Back strip	303 × 580 mm, 1.6 mm, on F2 (44 mm)	4	standing 30 mm inside the back wall	kerb radar tab, two call-light rows and drivers, LTE-M with eSIM and antenna, Wi-Fi/BT
Side strip	100 × 84 mm, 1.6 mm, on F3 (131 mm)	4	standing 30 mm inside the road-side wall	crossing camera tab and supplies
Sensor tabs (3)	16 × 16 mm, 0.8 mm, on 40 mm flex hinges	4	each on its sensor’s axis, the lens or chip just inside its window	IMX415 (approach, crossing), IWRL6432AOP (kerb radar)
Power board	105 × 200 mm, 1.6 mm	2	on the left wall, 120 V behind a printed shield	supply terminal, fuse, IRM-20-5, three feed sensors and ADC, three controller contacts and terminal, backup cell, charger

Lead L1 (power board to main board: 5 V on two pairs, cell sense, contact drive) is about 0.5 m of 20 AWG with Molex Micro-Fit 3.0 6-pin latched ends.

2. What is on the boards

Main board, side A (down): RK3576J (U1) with a 24 × 24 heat block (HS1) to the aluminium L-spreader, whose upright is bolted through the back wall to the steel pole bracket; LPDDR4X (U2), eMMC (U11), the SMD buzzer (BZ1) over the tone holes.

Main board, side B (up): decoupling field (C1), RK806S power (U3), 24 MHz and 32 kHz MEMS oscillators (Y1, Y2), ATECC608B (U8), ID chip (U9), the latched microSD (J1, reached by opening the door), LSM6DSOX motion chip (U13: the head hit or turned off its approach), eFuse (U42), lead header (J2), factory pads (TP1).

Corner board: approach camera tab (U260, IMX415 under a 102° M12 lens, 25° down the approach, through a 24 × 24 window in the door corner), the door tamper Hall switch (U7) facing a magnet on the door; camera supplies (U26) and ESD (U28) on side B.

Back strip, side A (to the wall): kerb radar tab (U250, IWRL6432AOP, 30° down toward the kerb and the crossing behind the 54 × 24 radome), 8 white LEDs behind the “seen you” slot (D11–D18) and 8 red LEDs behind the officers’ confirmation slot (D21–D28), each through a printed light guide. Side B: two light drivers (U70, U71), radar supplies (U24) and ESD (U27), the AP6275S (U5) with its antenna keep-out (ANT1) at the left edge, the BG95-M3 (U6) with its eSIM (U6S) and chip antenna (ANT2) in the top-left corner, 73 to 93 mm from the steel pole.

Side strip: crossing camera tab (U200, IMX415, 25° down to the stop line and the crossing, through the 56 × 28 window); supplies (U21) and ESD (U25).

Power board (side A into the head): spring-clamp supply terminal (J10) for the unswitched feed, fuse and varistor (F10), IRM-20-5 (PS1), three PCB current transformers (CT1–CT3) that the head’s own red, amber and green feed wires pass through unbroken, the ADS131M04 ADC (U51), the 18650 holder and cell (BT1) with its thermistor (RT1), the charger (U50), three photo-MOS contacts (K1–K3) and their 4-pole spring-clamp terminal (J11) for the controller’s own detector inputs, the lead header (J12).

3. Every connection, checked

Link	How	Checked against
Camera chips to RK3576J	4-lane MIPI CSI-2 each, over F1 or F3 and the tab hinges	IMX415 data sheet: 891 Mbps per lane; at 10 fps each uses 0.83 Gbps of 3.56
Radar chip	SPI and a frame interrupt over F2	TI IWRL6432AOP data sheet
Lamp feeds	the head’s own feed wires through the current transformers’ windows, never cut or tapped; the ADC on SPI over L1’s partner lines	Talema AC10 and TI ADS131M04 data sheets (to read)
Controller	three photo-MOS contacts on the controller’s own detector inputs, on spare conductors (or a separate detector cable where the authority asks)	Panasonic AQY212 data sheet (to read); NEMA TS 2 detector inputs
Call lights	PWM to two constant-current drivers on the back strip	driver data sheet (to choose)
LTE-M	USB 2.0 and UART over F2; eSIM soldered	Quectel BG95 hardware design
Wi-Fi/BT	SDIO and UART over F2	AMPAK AP6275S (RK3576 SDK default)
Power in	an unswitched 120 V feed, fused in the cabinet and on the board, into the class II IRM-20-5; 5 V on L1 into an eFuse at 3.5 A; L1 drops 0.03 V at 2 A	Mean Well IRM-20 data sheet
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

About 3.5 W from the RK3576J goes through the heat block into the aluminium L-spreader and on to the steel pole bracket and the 114 mm steel pole (5 K/W est.), so the chip sits near 78 °C with the head at 60 °C inside on a sunny summer afternoon (est.), under its 85 °C rating: to prove on rev A with a logger in a head in the sun. The camera and radar chips are 146 mm or more from the processor.

5. Power budget (est.)

State	Draw
Day: two cameras at 10 fps, radar, models, LTE-M	6.0 W
With the cell charging	about 7 W, 35 % of the 20 W supply
Night, quiet street: cameras at 5 fps, radar	4.5 W
Power cut (the crossing is dark): RK3576J asleep, wakes every 60 s to log and send the fault over LTE-M	0.4 W, about 26 h on the cell

6. Factory test (every board, every time)

Spring-pin fixture on TP1 and the strips’ pads: 5 V in, the eFuse trip at 3.5 A, every rail, boot from the card, a frame of a test chart from each camera, a corner reflector seen by the radar, all 16 call LEDs, the buzzer, the motion chip, the tamper switch with a magnet, the security chip’s key, the LTE-M and BLE links; on the power board, the supply under load, a test current through each feed sensor read back by the ADC, each controller contact closing into a test detector input, the charger’s temperature cut-off with the thermistor warmed. Each board gets its serial number in the ID chip.

7. Who makes what

One maker makes the rigid-flex piece and the power board, assembles them (turnkey) and makes lead L1 to length. We supply the microSD cards with our software and the lenses focused at 15 m (est.). The quote pack is /build/roadone-quote.

8. Cost per signal head, electronics (est.)

Item	Cost
V2 core (RK3576J, 4 GB LPDDR4X, 32 GB eMMC, power, AP6275S)	$48
Two IMX415 camera chips, holders and lenses	$28
IWRL6432AOP radar chip	$12
BG95-M3 LTE-M, eSIM and antenna	$18
Three feed sensors and the ADC	$9
Three photo-MOS contacts and terminal	$6
16 call LEDs, two drivers, buzzer	$4
IRM-20-5, terminals, fuse, cell, charger	$20
Security, ID, motion, socket, Hall switch, passives	$8
Boards (8-layer rigid-flex with a 580 mm back strip, three tabs, a 2-layer power board), 1,000 heads	$34
Lead L1	$2
Assembly and test	$14
microSD card with our software	$4
Total	about $207 per signal head (est.)

The bench head’s bought boards cost about $330 at qty 1 (Pi 5, two cameras, radar module, clamps, ADC and IMU boards, relays, LED sticks, Walter, supply, backup and small boards), so our boards are about $120 cheaper per head at 1,000 (est.).

9. Timeline

Step	When
Shape and placement (this page)	done, 4 Nov 2026
Rev T CAD: the boards in the signal-head CAD, every part checked in 3D; the approach, crossing and radar windows and the tone holes already moved	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 L-spreader and its bolts to the pole bracket, the tab brackets, the door magnet boss, the printed light guides and the 120 V shield.
The head’s inside temperature in full summer sun, logged on rev A; if the chip runs past 75 °C, a larger spreader on the back wall.
The highway authority’s cabinet wiring rules for the unswitched feed and the detector pairs in the signal cable.
LTE-M with the steel pole right behind the back wall.
The F1 and F3 camera-lane impedance over 274 and 131 mm with the flex 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
TI IWRL6432AOP: https://www.ti.com/product/IWRL6432AOP
TI ADS131M04: https://www.ti.com/product/ADS131M04
Talema AC10 current transformers: https://www.talema.com/current-transformers
Panasonic AQY212EH photo-MOS: https://industry.panasonic.com/global/en/products/control/relay/photomos
Quectel BG95-M3: https://www.quectel.com/product/lpwa-bg95-m3/
AMPAK AP6275S: https://www.ampak.com.tw/
Mean Well IRM-20: https://www.meanwell.com/Upload/PDF/IRM-20/IRM-20-SPEC.PDF
ST LSM6DSOX: https://www.st.com/en/mems-and-sensors/lsm6dsox.html
Microchip ATECC608B: https://www.microchip.com/en-us/product/atecc608b
TI DRV5032: https://www.ti.com/product/DRV5032
Samsung INR18650-35E: https://www.samsungsdi.com/
NEMA TS 2 traffic controller assemblies: https://www.nema.org/standards/view/traffic-controller-assemblies-with-ntcip-requirements
The signal head: products/roadone/cad/roadone-cad.mjs (rev A, windows rev T); the boards: products/roadone/hardware/pcb/roadone-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. RoadOne’s boards were made with every rule from the start: 16 pass, 5 fixed, 12 to prove, 0 fail. The full review, with every number and its source, is on the board page. It shows:

Camera pixels: a car 60 m up the approach fills about 65 px against a 30 px need; a person reaching the far kerb (8.7 m) about 112 px against 20; both 8 MP chips at 10 fps use 23 % of their links and 166 Mpx/s of the image processor’s 480.
Every crossing call in view: the first car waiting, the queue 20 m back, a vehicle 60 m out, a cyclist in the kerb lane and the opposing lane; a car over the stop line, people in both lanes and at the far kerb, a near miss and a car stopped on the studs; people waiting at and back from the kerb, stepping on and still in the near lane, from where each lens or chip really sits in its wall.
The approach camera looks out of the door corner (fixed): from the floor the 60 m count line lies 88° off the window (lesson: window). The crossing window and the radar slot were also sized for our chips (fixed). Drawn in the CAD the same day.
The controller’s own lamp drive is untouched (fixed): an unswitched supply on a spare conductor, and feed sensors the wires pass through unbroken, so a dead red module is still seen by the controller.
The latched microSD (J1) is fitted, and our software starts from it; updates run only in the quiet hours, and the controller keeps its own timings throughout.
A thermistor on the backup cell holds charging outside 0 to 45 °C, and conformal coating against rain and condensation 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 head’s temperature in summer sun (78 °C est. at the chip), the AI time, the power-cut run on the cell, LTE-M near the steel pole, the authority’s wiring rules for the controller contacts, 120 V creepage, the tab brackets, the flexes, the tamper magnet and the boards in the rev T CAD.

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