A 60 mm disc that shows your current mode to the people around you, as a glyph on a 25 × 25 dot matrix. The app reads the body, the pendant only signals.
Engineering proposal | 72 h battery | No subscription
Fig 1MODE™ · Physical indicatorTap or press Space to take apart0.0 mm apart · 925 mWh ÷ 12.8 mW = 72 h
The matrix: 489 cells, the glyph the app sendsCoil, board, cell, matrix, louvre, diffuser, glass, bezelBack cap and band stay putThe pendant alone, no stand. Plausible engineering, imagined from the case: only the 60 mm disc, the domed glass, the thin metal ring, the 25 × 25 matrix with its four glyphs and the 72 h claim come from MODE. The 250 mAh × 3.7 V cell holds 925 mWh, and 925 mWh ÷ 12.8 mW ≈ 72 h because the glyph is lit 4 s at about 48 mW, then dark 11 s at 0.07 mW, with a full 15 s glow after each status change.
Documentation
How MODE™ would be built
A short engineering proposal for the pendant above. Facts from the case are marked Case. Everything else is imagined, but uses real parts you can buy today. Hover a row to find the part in the figure.
01What it is
MODE™ is a 60 mm disc that shows your current mode to the people around you, as a glyph on a 25 × 25 dot matrix.
The app reads the body and decides the mode. The pendant has no sensors and only signals it.
72 h battery life
Recycled materials
No subscription
02How it works
The phone does the thinking. The pendant gets one small message when your mode changes, and turns it into light.
Signal path
1AppReads physiology from other wearables and picks the status.Case
2Bluetooth LEAbout 6 bytes, over the low power radio phones use for watches.Encrypted by the bond
3MicrocontrollerA tiny computer with the radio built in. Picks the animation from its own memory.nRF54L15 · #3
4LED driverSets a brightness for every dot, 30 times a second.2 × IS31FL3741A · #6
525 × 25 matrix489 white LEDs behind a black grid and a frosted sheet.The glyph · #6
Power path
1Charging padAny Qi pad, the standard phone charging pad.Not in the box
2Receiver coilPicks up energy through the non metal back.Qi coil · #2
3Charger chipTurns coil power into a safe battery charge.BQ51050B · #3
4Battery250 mAh round cell. Feeds the LED drivers directly.Li-polymer · #5
5RegulatorA steady 1.8 V for the microcontroller only.TPS62840 · #3
03Bill of materials
Every part, bottom to top. The number matches the callout on the open figure. Rows with the same number belong to one assembly.
Rough unit cost at 10k units, in USD, checked against distributor listings in October 2026.
#
Part
What it does
Example component
Size, mm
USD
1
Band and back cap Case
Holds everything, takes knocks, lets radio and charging through the back
Recycled 6000 series aluminium band, CNC and anodised. Back cap in glass filled recycled PC or zirconia ceramic, not metal
Ø60 × 9.9
5.50
2
Receiver coil
Picks up energy from a Qi pad
Round Qi coil with ferrite shield, Superworld SCR35018R3KB class, or a custom Ø37 coil
Ø38 × 1.1
1.20
3
Main board
Carries the brain, radio, charger and antenna
4 layer FR4, ENIG finish
Ø52 × 0.8
0.70
Microcontroller with radio
Runs the firmware, talks Bluetooth LE, stores the animations
Nordic nRF54L15, QFN48. 1.5 MB on chip memory, so no extra flash chip
6 × 6
2.30
Qi receiver and charger
Turns coil power into a safe battery charge, in one chip
TI BQ51050B, VQFN20
4.5 × 3.5
1.80
Regulator
Makes a steady 1.8 V for the microcontroller, sips 60 nA when idle
TI TPS62840, VSON8
2 × 1.5
0.60
Crystals
Keep the radio on frequency and the clock on time
32 MHz, 2016 size. Optional 32.768 kHz, 3215 size
2 × 1.6
0.20
Antenna
Sends and hears Bluetooth
Meander trace printed on the board edge. Chip option Johanson 2450AT18A100
Trace
0.00
Connector and passives
Joins the matrix flex. Small resistors and capacitors
10 pin 0.5 mm pitch flip lock FPC connector, about 25 passives
6.4 × 2.2
0.45
Ambient light sensor
Optional. Dims the glyph in dark rooms, brightens it outside. Not a body sensor
Lite-On LTR-303ALS-01
2 × 2 × 0.7
0.40
4
Four screws
Clamp the main board to the case bosses
M1.2 stainless pan screws
Ø1.2 × 1.4
0.08
5
Battery Case 72 h
Stores the energy for 72 h
Custom round Li-polymer pouch with protection board, Grepow round series. Their 2537036 holds 210 mAh in Ø36 × 2.45
Ø40 × 3.5
2.50
6
Matrix board and flex
Holds the 489 LEDs in a circle, joins the main board
4 layer FR4 with a polyimide flex tail
Ø56 × 0.7
1.25
489 white LEDs Case
The dots of the glyph, 25 × 25 in a circle
0402 white chip LEDs, OSRAM CHIPLED 0402 (LW QH8G), one tight brightness bin
One window per LED, so light can't bleed into the next cell
Black PC, injection moulded
Ø55.6 × 1.0
0.25
8
Frosted sheet
Turns each LED point into an even soft square
Opal PC film with black printed mask
Ø55.6 × 0.4
0.15
9
Gasket Draft
Keeps water and dust out
Silicone or PSA foam ring
Ø57.4 to Ø59.8 × 0.4
0.10
10
Domed glass Case
Protects the face, gives the dome highlight
Chemically strengthened aluminosilicate, anti reflection coated. Sapphire costs about 4× more
Ø58 × 1.9
2.50
11
Metal ring Case
Holds the glass down. The thin satin edge you see
Recycled aluminium, satin, press fit and bonded
Ø60 × 0.8
1.20
Parts total
28.68
Built: board assembly, about 560 placements, Qi and radio test, LED calibration. Before packaging and charger
≈ 33
04Power budget
Battery: 250 mAh × 3.7 V = 925 mWh. A round cell this size holds about 300 mAh new. 250 mAh is what it still holds after a few hundred charges.
The key decision: the glyph is not lit all the time. The face pulses, lit 4 s and dark 11 s, every 15 s. After every status change the first glow holds a full 15 s. The two LED drivers alone draw about 3.6 mA each whenever they are awake, so lit all the time a typical day would last only about 19 h.
State
What draws power
Current
At 3.7 V
Face dark
Microcontroller asleep 3 µA, Bluetooth link at 1 s 8 µA, drivers shut down 1 µA, leakage 8 µA
LEDs: about 0.1 mA per fully lit dot gives roughly 500 cd/m² behind the diffuser, like a phone screen indoors. A typical day (40% Available, 30% Focus, 20% Recover, 10% Overloaded) averages about 49 fully lit dots.
Worn all day in one mode: Focus 108 h, Recover 81 h, Available 73 h, Overloaded 33 h. Charging on any Qi pad at about 125 mA, full in about 2.5 h.
What would break it: a day stuck in Overloaded (33 h), always on (19 h), or full sunlight brightness (about 3× the LED current).
05Assembly order
Bottom to top, the same order as the exploded view.
Case. The back cap is bonded into the band on a fixture. The threaded brass inserts are already in the bosses.#1
Charging coil. Glued into the seat ring on the back cap, ferrite down, leads up.#2
Main board. Dropped in over the coil. The coil leads are soldered to two pads.#3
Board screws. Four screws clamp the board edge to the bosses.#4
Battery. Laid on its foam pad. The two nickel tabs are soldered to the board.#5
LED matrix. Placed on top of the cell. Its flex tail is pushed into the connector and locked. The two drivers sit on its underside, in the ring outside the battery.#6
Louvre, then diffuser. Keyed so every window lines up with its LED.#7, #8
Seal, glass, bezel. Gasket on the band, glass on the gasket, bezel pressed and bonded over the glass edge.#9 to #11
Test. Charge on a Qi pad, pair, light every dot under a camera and store a per dot brightness correction, then an air leak test.
06Firmware in short
No buttons and no ports. Placing the pendant on a charger wakes it and opens pairing for 2 minutes.
State
What happens
Sleep
From the factory, or when the battery is empty. Radio off, about 2 µA. Wakes on a charger.
Connected
Bonded to the phone, link at a 1 s interval, face dark between pulses.
Showing glyph
Drivers awake, frames read from memory at 30 fps, the 4 s on, 11 s off pulse.
Charging
Shows battery level for 5 s, then goes dark. Updates install only here.
Low battery
Below 10% the pulses get shorter and dimmer, and the app gets a warning. At 3% it shows one dot, then sleeps.
Link lost
Keeps the last status for 30 min, then fades to a single centre dot until the phone is back.
The app writes only when the status changes, usually a few times an hour. A change shows within about 1 s. Battery level goes back through the standard Bluetooth battery service.
Animations live on the pendant. Each frame stores 4 levels per dot, so 489 dots take about 120 bytes. An 800 frame glyph needs about 100 KB, and all four fit in the chip's own memory.
OTA updates (new firmware sent over the air) are signed and go through Nordic's MCUboot in two slots. The new image is checked first and the old one is kept, so a failed update falls back. New glyphs can arrive the same way.
07Open questions and risks
The LED driver is the battery. 489 dots need two IS31FL3741A chips, 702 dots of capacity, and they draw about 7 mA whenever they are awake. That is why the glyph pulses. A driver that idles near 1 mA would let the face stay lit.
A metal back blocks charging and Bluetooth. An aluminium back cap would heat on a Qi pad and trap the radio. The back must be glass, ceramic or plastic. The band and bezel can stay metal.
Drivers belong on the matrix board. They reach the 489 LEDs through 96 lines. Placed under the matrix board, in the ring outside the battery, the flex needs only about 8.
Round battery. A Ø40 × 3.5 round cell is custom, with a tooling fee and a 3 to 4 month lead time. A D shaped or stock rectangular cell is the fallback, with less capacity.
Water and certification. With no ports, IP67 (dust tight, survives a dunk) is realistic, but needs a vent membrane or bonded glass. Certification: CE radio, FCC, Bluetooth listing, Qi logo (optional), UN38.3 and IEC 62133 for the battery.
Even dots. 489 LEDs vary in brightness and tint. Buy one tight bin and calibrate every dot at the factory. Heat is not an issue: even Overloaded peaks near 0.1 W.
08Parts up close
Every part on its own. The number in the corner matches the callout on the figure above. Hover or tap a card and the part lights up in the assembly.
The assemblies are drawn at one scale. Chips and small parts are enlarged, the multiplier is in the top right corner. At the bottom, all chips side by side at true scale.
Assemblies, bottom to top
Band and back cap
Holds everything, takes knocks and lets radio and charging through the back.
Ø60 × 9.9 mm
01
Material
Recycled 6000 series aluminium band, CNC and anodised. The back cap is not metal: glass filled recycled PC or zirconia ceramic.
Example
Band on CNC, threaded brass inserts in the cap for the screws. The loop on top is imagined.
Receiver coil
Picks up energy from a Qi pad, the standard phone charging pad.
Ø38 × 1.1 mm
02
Material
Ferrite shield and a flat copper litz wire winding, 11 turns.
Example
Superworld SCR35018R3KB (Ø35, 1.2 mm tall) or a custom Ø37 coil.
Main board
Carries the brain, radio, charger and antenna.
Ø52 × 0.8 mm
03
Material
FR4, 4 layers, ENIG finish.
Example
nRF54L15, BQ51050B, TPS62840, a 32 MHz crystal, the FPC connector and a trace antenna along the board edge.
Four screws
Clamp the main board edge to the case bosses.
Ø1.2 × 1.4 mm, head Ø2.9
04×9
Material
Stainless steel.
Example
M1.2 pan head screw.
Battery
Stores the energy for 72 h.
Ø40 × 3.5 mm, 250 mAh
05
Material
Li-polymer pouch cell with a protection board, nickel tabs and a PE foam pad.
Example
Grepow round series: their 2537036 holds 210 mAh in Ø36 × 2.45 mm.
Matrix board and flex
Holds the 489 LEDs in a circle and joins the main board.
Ø56 × 0.7 mm
06
Material
FR4, 4 layers, polyimide flex tail.
Example
489 OSRAM CHIPLED 0402 at 2.2 mm pitch, two IS31FL3741A drivers underneath.
Black grid
One window per LED, so light can't bleed into the next cell.
Ø55.6 × 1.0 mm
07
Material
Black PC, injection moulded.
Example
One moulded part, a square window for each of the 489 LEDs.
Frosted sheet
Turns each LED point into an even soft square. This is the face you see.
Ø55.6 × 0.4 mm
08
Material
Opal PC film.
Example
Film with a black printed mask around the cells. The drawing shows the Available glyph.
Gasket
Keeps water and dust out.
Ring from Ø57.4 to Ø59.8, 0.4 mm thick
09
Material
Silicone or PSA foam tape.
Example
Sits on the band, under the glass and the metal ring.
Domed glass
Protects the face and gives the dome highlight.
Ø58 × 1.9 mm: edge 0.7, dome 1.2
10
Material
Chemically strengthened aluminosilicate glass, anti reflection coated.
Example
Sapphire works too, but costs about 4× more.
Metal ring
Holds the glass down. This is the thin satin edge you see from outside.
Ø58.2 to Ø60, 0.8 mm tall
11
Material
Recycled aluminium, satin finish.
Example
Pressed and bonded over the glass edge.
Chips and small parts, on their footprints
Microcontroller with radio
Runs the firmware, talks Bluetooth LE and stores the animations.
6 × 6 mm
03×5
Material
QFN48 package: 12 pins per side and a pad underneath.
Example
Nordic nRF54L15. 1.5 MB of memory on chip, so no extra flash is needed.
LED matrix driver, 2 pcs
Lights each dot at its own grey level. They sit under the matrix board, in the ring outside the battery.
7 × 7 mm
06×4
Material
QFN60 package: 15 pins per side and a pad underneath.
Example
Lumissil IS31FL3741A: 39 × 9 = 351 dots, 256 brightness steps. Two are enough for 489 LEDs.
Qi receiver and charger
Turns coil power into a safe battery charge, in one chip.
4.5 × 3.5 mm
03×6
Material
VQFN20 package with a pad underneath.
Example
TI BQ51050B.
Regulator
Makes a steady 1.8 V for the microcontroller and sips 60 nA when idle.
2 × 1.5 mm
03×11
Material
VSON8 package: 4 pins on each of two sides and a pad underneath.
Example
TI TPS62840.
White LED 0402, 489 pcs
One dot of the glyph.
1.0 × 0.5 mm, 2.2 mm pitch
06×19
Material
Chip LED with two end contacts.
Example
OSRAM CHIPLED 0402 (LW QH8G), all from one tight brightness bin.
Flex connector
Takes the matrix flex and locks it with a flip bar.
6.4 × 2.2 mm
03×6
Material
10 contacts at 0.5 mm pitch, flip lock.
Example
10 pin FPC connector. Next to it on the board, about 25 small resistors and capacitors.
32 MHz crystal
Keeps the radio on frequency.
2 × 1.6 mm
03×11
Material
2016 size package, four contacts in the corners.
Example
32 MHz in a 2016 package. Optionally a second one, 32.768 kHz in a 3215 package, for the clock.
Ambient light sensor Proposal
Dims the glyph in a dark room and brightens it outside. Not a body sensor.
2 × 2 mm
03×10
Material
2 × 2 × 0.7 mm package with a clear window.
Example
Lite-On LTR-303ALS-01. For auto brightness only.
At true scaleOne cell is 1 mm. All parts at one scale, seen from above. The smallest, the 0402 LED, is half a cell, and the matrix carries 489 of them.
09Cross section
The assembled pendant, cut through the centre. The proportions are true, only enlarged. On the right, the thickness of every layer from the back cap to the top of the dome, 12.2 mm in total.
At the edges you see the band, the gasket and the metal ring. The cut runs through the microcontroller on the right and the Qi receiver on the left. The screw on the right sits just behind the cut plane, so it has no hatching.
Layer
#
mm
Glass: edge 0.7 and dome 1.2
10
1.9
Air gap
1.0
Frosted sheet
08
0.4
Black grid
07
1.0
Matrix board with LEDs
06
0.7
Battery
05
3.5
Foam pad
05
0.3
Main board
03
0.8
Coil: ferrite and winding
02
1.1
Back cap
01
1.5
Total
12.2
MetalPlasticFR4 boardBatteryChipGlassBehind the cut plane
10Fact source
From the case
Flat 60 mm disc
Domed glass, matte black face, thin metal ring
25 × 25 circular matrix, 489 square cells, white and grey levels
4 statuses: Available, Focus, Recover, Overloaded
72 h battery
The app reads physiology, the pendant only signals
Recycled materials, No subscription
Draft only, not published: 12 mm thick, LED Matrix, Wireless charging, Weather sealed
Engineering proposal (imagined)
Every chip, part number and price
Aluminium band with a non metal back cap
0402 LEDs, two IS31FL3741A drivers, black louvre, diffuser
Bluetooth LE packet, firmware states, OTA updates
250 mAh cell and the 4 s on, 11 s off pulse that reaches 72 h
Ambient light sensor for auto brightness (optional)
