Reckoner

Turns press-and-hold motorised blinds into Home Assistant covers.
One Reckoner per blind, hidden in the wall box behind the buttons you already have.

[!CAUTION] This board switches 230 VAC mains and is not isolated. Every part of it, including the ESP32 and the programming pads, is live whenever it is connected. A mistake can kill you or start a fire inside your wall. If you are not qualified to work on mains wiring, do not build or install it. Read Safety first.

What it does

Motorised blinds with press-and-hold buttons have no idea where they are. The Reckoner sits in the wall box between those buttons and the motor, and fixes that.

• Your buttons keep working, with or without Wi-Fi. One press runs the blind to the end; another press stops it.
• For Home Assistant. The blind is a cover: open, close, stop, set position and report position.
• It knows where the blind is, without a sensor. It uses dead reckoning: a known start, the calibrated time for a full stroke and the time elapsed. At each end the motor's limit switch cuts the current; the Reckoner sees the drop, takes a fix and clears the drift.
• It survives power cuts. It notices mains loss within one cycle and saves the position on the energy left in its capacitors.

How it works

K2's common is fed through K1, so up and down can never be live at the same time, not even with a firmware bug or a welded contact. Both relays are held off by hardware through reset, boot and flashing.

The board is 70 × 54.5 mm on two layers, routed by hand, with 3 to 5 mm between mains nodes. The production files for JLCPCB are in PCB/production/.

Bill of materials

Shipping and taxes: JLCPCB $24.28 (after a $10 coupon), LCSC $30.17 (shipping and tariff, after $3.05 of discounts), Digi-Key $35.29 (€25.00 shipping and €6.44 VAT). The same table is in bom.csv.

Safety

[!WARNING] There is no low-voltage side. Circuit ground is mains live (L), so the ESP32, the LED, the test pads and every trace sit at 230 VAC to earth whenever L and N are connected. Only the enclosure protects you.

• "Off" is not safe. Only isolating the circuit at the breaker makes the board dead, and C1 and C2 (400 V) can stay charged after that: measure them before you touch it. The motor wires J5 and J6 reach about 460 VAC while the motor runs.
• Never connect USB, a debugger, a laptop or a grounded probe while it is on mains. Their ground is earth; this board's ground is L.
• Never touch it while it is connected, not even "just the logic side". There is no logic side. There is only the death side!
• Never power it without an insulating enclosure, and never mount it in a metal box.
• Never work on live mains alone. Have someone with you who can give first aid.
• Installing: leave it to a qualified electrician, and isolate and prove dead first. The circuit needs a breaker of 16 A or less and a 30 mA RCD.
  • J1 goes to L and J2 to N (they can't be swapped). The buttons' common must be on the same L as J1.
  • J3 and J4 go to the button outputs, J5 and J6 to the motor's up and down wires. The motor's neutral stays on house N.
  • The motor must be a 230 VAC tubular motor of about 1 A with its own limit switches.
• Flashing and testing: flash only with mains disconnected at the source, through the USB pads TP1 to TP4 (TP5 to GND for download mode); after that, updates go over the air. Test live only through an isolation transformer and a series-lamp limiter, with isolated probes.

[!IMPORTANT] Blind Reckoning is a hobby prototype I built for Hack Club Half Life. It is not a certified product and has not been tested by any laboratory. Everything here is provided as is, without warranty. If you build, flash, test or install a Reckoner, you do so entirely at your own risk. The authors accept no responsibility for injury, death, fire or damage to property.

The Blind Reckoning "brand" is just a game. Please do not take it too seriously ;)

Status

Designed, routed and costed; boards and parts are next to order. The enclosure (CAD/) and firmware (Firmware/) are not started.

Licence

These licences apply retroactively: any copy of the hardware or documentation from any commit of this repository, including commits made before the licence files were added on 2 October 2026, is licensed under these terms.

Copyright 2026 KOZELJ Michele. Source location: https://github.com/blind-reckoning/Reckoner. If you make hardware from this source, keep the source location visible on the board or enclosure where practicable (CERN-OHL-S v2, section 4).

Not covered: the Blind Reckoning name and logos (brand/logos/, brand/symbols/), which are not licensed for reuse, so modified hardware needs its own name (see the brand book); the fonts in brand/fonts/ (SIL Open Font License 1.1); and KiCad's library symbols and footprints (KiCad library licence).