dekuNukem defeated Daan Tech's Bob cartridge DRM to refill at 1/60 the price

Daan Tech's Bob is a sleek countertop dishwasher that needs no plumbing, and its headline convenience is the Bob Cassette: a drop-in cartridge with detergent and rinse aid for 30 washes. Daan sells refills at £43 ($60) for 90 washes once shipping and VAT are added — 48p (67c) per wash, or about £174 a year for daily use. The obvious alternatives were to pay the subscription or pour detergent manually, which the maker warns against because dosing and multi-stage rinsing are hard to reproduce.

dekuNukem treated the cartridge as a system to audit rather than a bill to pay. Four wires to the receptacle suggested an I2C EEPROM, so he melted the casing open with a soldering iron and found a 24C02 chip — 256 bytes of memory with pull-ups and diodes. He dumped it through a USB-A socket using a leftover board, ran one wash, dumped it again, and found exactly one byte changed at address 0xa1. Decoding the sequence showed it was washes-left XOR 0x50; writing 0x4e reset a cassette to 30 washes. Setting a nonsense value produced '111 washes', proof that nothing else validated the count.

Resetting the counter was only half the job — the cartridge still needed liquid. Weighing the machine's waste water gave the real dosing: 4.33 mL of detergent and 1.17 mL of rinse aid per wash. That turned Daan's vague 'secret sauce' into two measurable concentrations, and regulation did the rest: every chemical sold in the UK carries a Safety Data Sheet, and matching UFI numbers later identified Daan's exact detergents. Two 5-litre jugs from a catering supplier cost about £17 and cut the running cost to 0.80p per wash — roughly 60 times cheaper, a 98% saving — with dishes just as clean.

He then productized the fix: a small hand-soldered board called Bob Rewinder that plugs into the cassette and resets the EEPROM at the push of a button, sold through Tindie, with the whole investigation, user manual and detergents documented on GitHub. The writeup drew 1,260 points and 404 comments on Hacker News within weeks of its May 2021 post, and the irony was not lost on the author: Daan markets an environmentally friendly 'positive cycle' while shipping single-use plastic-and-electronics cartridges at 60 times the cost of the bulk chemistry inside them.

Attack the lock itself: read the cartridge's 256-byte chip, decode the one-byte wash counter, and match the chemistry via regulated safety sheets.

The lock lived in a commodity 24C02 chip with one XOR-obfuscated byte and no bound checking, so cheap tools plus a single wash-diff revealed the whole counter scheme.

Measuring the machine's real water use turned 'proprietary detergent' into two exact dilutions, making any equivalent chemistry comparable.

Public Safety Data Sheets and UFI identifiers let him verify substitutes by composition instead of guessing, so the refill was evidence-based rather than hopeful.

The fix preserved the set-and-forget convenience — refill by syringe, renew with one button — which is why he used the machine more, not less, afterwards.

Open-sourcing the method let the fix scale beyond one kitchen: 1.5k GitHub stars, 74 commits, a user manual, and a Tindie board anyone could buy.

Locking a commodity consumable behind a one-byte counter just invites the refill: if the chemistry is not genuinely proprietary, build the moat in formulation, service or convenience — not DRM.

dekuNukem began selling Bob Rewinder boards on Tindie, with a user manual for safe refilling. By May 2021 the writeup had drawn 1,260 Hacker News points; a late-May update identified the apparent exact detergents through UFI numbers, and a March 2022 update added more ingredient findings. Once the DRM cost was gone the author stopped rationing washes and ran the machine several times a day; the subscription economics and the trivial counter chip remain documented in public for any owner to reproduce.