Bob is a countertop dishwasher designed for convenience: you add the water and detergent as-needed, so there's no need for plumbing hookups. The detergent, though, comes in DRM cartridges and costs an arm and a leg—in effect, the dishwasher is a hook to get you buying detergent that costs more than $200 a year if you wash daily. The good news is the DRM was hacked, allowing you to "rewind" Bob detergent cartridges and refill them.
Only one byte is different at address 0xa1, and it went down from 0x4A to 0x49 while going from 26 to 25 washes. Doing some interpolation, it seems that byte starts from 0x4e at 30 washes, and goes down from there. I changed it to 0x3f, which should be 15 washes, and put it back. This happened: 111 washes! Looks like they didn't do much bound checking 😅.
Turns out the "highly concentrated" dishwasher detergent that is "not publicly for sale" and too dangerous for users to handle themselves is on Amazon for 20 cents a fluid ounce.
With that, the total cost per wash is: 0.62p + 0.18p = 0.80p, or 1.1 US cents! We know from earlier that Bob Cassettes costs 48p (67c) per wash.Therefore, refilling it yourself is more than 60 times cheaper, resulting in a massive 98% cost saving compared to buying new!
I have to say I respect the deranged audacity of selling 30-use plastic cartridges as "fighting against single-use plastic."
