We have an OKI ES 3640 Pro MFP. The printer has apparently no sensor to measure the amount of toner left, only a counter in the chips which are in the cartridge. To me this is verry odd and wastefull, because althoud it said that yellow is empty, the yellow parts of a print weren't faint at all.

The printer communicates with the cardridge in an NFC like way. But it's doesn't seem to be normal RFID, because none of our reader could read the chip of the cardridge.

Interesting! Can't wait to hear more. Did you pull these out of toner cartridges or source them direct? What toner models are these used in and do you have any pictures of where they are in the toner assembly?

Funnily enough, when i hooked up somes wires to the capacitor of the tank circuit of the original DRM chip to look at the transaction with an O-scope, for some reason the printer recognised the cardridge as full.

Maybe the wires intorduce some RF woodoo into the system oder maybe I zapped the IC while soldering.

This was mainly a for profit profit project (i wanted to be able to print again). Due to the lack of time at my hands atm I will probably shelf this project, but not abandon it.

Well, sounds like you found the way to defeat the system ;-)

I used to have a Brother printer that had a little window in each side of the toner cartridge. It was using optical sensor to see if toner was blocking the path. Just put a piece of blue tape over that window and you could keep printing. I don't mind features like this that ensure you get the best prints, but in the manual they should document this kind of hack for when you're in a pinch, or just want to print some stuff that doesn't need to look perfect and thereby make the most out of the wastefulness of cartidges that often don't get recycled.