OxyCart
The home oxygen cylinder cart, made smart: it weighs the backup cylinder, shows hours left at the real flow, and turns a power cut into 'switch to the cylinder, 4 h 50 min left'
A cylinder cart for the backup E cylinder whose cup sits on a load cell. It knows how many grams of oxygen are left, measures the real flow from the weight slope, shows hours left and the swap-by time on e-paper, and sends a refill reminder before the 200 psi reserve. The FlowTee, an inline ultrasonic sensor on the concentrator outlet, logs flow, hours of use and purity and senses mains loss, so a power cut gives an instant beep and a family phone alert with the cylinder's hours left. It monitors and alerts only; it never sets or switches the oxygen flow.
- Who buys it
- First: families of people on long-term oxygen at home (about 887,000 Medicare users rely on oxygen equipment), who today read a pressure gauge on a $117-185 cart. Next: home oxygen (DME) suppliers who pay for emergency cylinder runs; hospital digital cylinders (Linde LIV IQ, Air Liquide Takeo, Airgas Intelli-OX) are not sold into homes.
- Why it pays
- Fewer surprise empty cylinders and emergency deliveries, and no guessing in a power cut. For a DME supplier, each avoided unplanned delivery is the saving (est.); for the family, the value is knowing the hours left without reading a gauge.
- Target price
- $199 kit (cart + FlowTee), $129 cart alone + $4 per month for phone alerts (target); DME fleet pricing on request
- First-minute wow
- The lights go out at 21:10. The concentrator stops, the FlowTee beeps, and the daughter's phone says 'Power cut at Mum's. Concentrator stopped. Cylinder on the cart: 4 h 50 min at 2 L/min.'
What the research found
And how this design answers it
- People find cylinders empty only when breathless (MIJA case study) → the cart watches the weight all day and warns before the 200 psi reserve
- Gauge reading is ±9 min at 2 L/min and a cylinder brought in from a cold car reads up to 24 min high (CAD contents report) → weight does not care about temperature
- Users turn the flow up and the time-left sum is wrong → the weight slope measures the real flow (±11% after 10 min at 2 L/min)
- Cheap concentrators can lose purity with no alarm (The Quint: 30-90% purity on some imports) → the FlowTee logs purity and flow at the outlet
- In a power cut the router dies too, so a Wi-Fi alert cannot leave the house → the FlowTee beeps at once and the cloud alerts the family when both units fall silent together
- The cylinder leans on the cart and friction steals weight → a loose collar with a PTFE liner and a level gate keep the error to 8-15 g (3-6 min, CAD lean report)
Use case
Evening power cut, father on 2 L/min at home
Person on oxygenFamily member away from homeHome oxygen supplier
- 01Trigger: the power fails at 21:10 and the concentrator stops
- 02Detection: the FlowTee sees its USB power drop and beeps; the cart still has 772 g of oxygen in the E cylinder
- 03Alert: the cart shows 'Use the cylinder: 4 h 50 min at 2 L/min'; 3 min later the family's phone gets the power-cut alert with the hours left
- 04Action: the cannula goes on the cylinder; at 2 h left the supplier gets a delivery request
Outcome: No guessing in the dark, and the supplier is called with hours to spare, not minutes (est.)
How it works
Architecture
- 01
Sense: TAL220 load cell under the cylinder cup, LIS3DH level gate, Gasboard-7500H ultrasonic O2 purity and flow sensor, USB VBUS for mains
- 02
Decide: XIAO ESP32-C3s compute grams left, flow from the weight slope, hours left, purity and flow drift, and power-cut state
- 03
Send: Wi-Fi MQTT/TLS heartbeats every minute; the cloud treats both units going silent together as a probable power cut
- 04
Tell: e-paper hours left on the cart, local beep, family phone alerts, and a refill request to the supplier at a set number of hours
Hardware
Real parts, buyable today
Bill of materials: about $92 per cart and $83 per FlowTee at qty 1, $175 the kit (est.).
| Block | Part | Why this part |
|---|---|---|
| Weighing | TAL220 10 kg straight-bar load cell + HX711, 0.8 mm overload stop | Full E cylinder with regulator is about 5 kg; 2 g averaged noise is under a minute of oxygen at 2 L/min (est.) |
| MCU + display | Seeed XIAO ESP32-C3 + Waveshare 2.13" e-paper | Hours left stays on screen with no power; about 78 days per 18650 charge (est.) |
| Level gate | Adafruit LIS3DH | Readings are used only when the cart is still and within 1 degree of level |
| FlowTee sensor | Cubic Gasboard-7500H ultrasonic O2 sensor | 20.5-95.6% O2 ±1.5% FS and 0-10 L/min ±0.2 L/min in one 80 x 25 x 22 body, no calibration gas |
| Cart | Printed ASA case on 4 x 50 mm casters, 1.02 kg steel ballast, Ø19 mast, loose collar | Tips at 11.8-17.9 degrees with a full cylinder (CAD tip report) |
Mechanical
Printable CAD
6 parts, generated from code and checked as closed solids. Pick a part to inspect it, or download the STL files to print.
See the CAD parts render
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Bought hardware fitted inside this part (checked in the CAD: nothing collides with the plastic)
- Scale case: load-cell pillar and overload stop, steel ballast pockets, battery and boards, mast socket, USB-C and buttonscale-case.stl · ASA
- Scale lid: e-paper pocket and window, holes for the cup post and the mastscale-lid.stl · ASA
- Cylinder cup: the E cylinder stands in it, post down to the load cell, drain holescylinder-cup.stl · ASA
- Guide collar: clamps the mast, loose ring round the cylinder so it never takes weightguide-collar.stl · PETG
- FlowTee case: ultrasonic O2 sensor with ports through both ends, MCU, reserve LiPo, buzzerflowtee-case.stl · PETG
- FlowTee lid: light-pipe hole, counterbored screwsflowtee-lid.stl · PETG
Open risks we are working on
- The tare of each swapped cylinder is unknown: until it is learned, time left is ±17 min at 2 L/min, no better than the gauge (CAD contents report)
- Purity readout = oxygen gas analyzer (21 CFR 868.1720, Class II): US rev A ships with flow and power-cut only until a 510(k) (gate R2)
- The cart tips with only 5-8 N at the handle with a full cylinder; it is not a walking aid (CAD tip report, test T2)
- Gasboard-7500H price, port size and back-pressure on the concentrator are unconfirmed (quote and bench test T3)
- Linde, Air Liquide and Airgas already sell digital time-left cylinders to hospitals and could bring them home
- No family or DME interviews yet (gate G1: 10 families + 3 home oxygen suppliers)
Design stage only: nothing on this page is for sale. Specifications and prices are targets.