Spoofing a fluid/ink sensor (not the chip, but the fluid presence sensor)

[davidDac]

Hey all, this is my first post, so hello to everyone!

I've been 3d printing on my little Anet A8 little ink cartridge chip caddys for my inkjet printer (Epson) to hold them tight against the ink chip main PCB.

But, I found that in each ink cartridge is a little fluid sensor glued into the wall of a little reservoir that the ink passes through as it leaves the cartridge. Given the cost of a head getting damaged by running dry, it was probably a smart move by Epson to put these in so if the reservoir runs empty, the printer can sense that and not print (printing heats up the head significantly, to the point where the ink plays a role in keeping it cool as it ejects (I believe from other posts).

I'm trying to find out how I can spoof this little sensor but know nothing about them. I attached a pic, and you can see (this is the outside of the ink reservoir view) that coming in from both sides are stainless steel contacts made of thin sheet metal. I'm wondering if this has anything to do with the sensor as they could have used wire? or, the stainless steel is easy for assembly because it's form allows it to be snapped easily in place. In between the two stainless contacts is the sensor, and it appears from this outside the reservoir view that the sensor does not continue all the way across to the right side (maybe the ink makes the final contact to close the circuit?). The other side of this sensor is a little plate with 2 holes to let ink into a tiny little box (2mm squarish) for the fluid from the reservoir to flow into and activate the sensor.

When I read the sensor on a multimeter for continuity, there is none, either with fluid in it or not. When I read the sensor for capacitance, I get a reading of .25nF. There is a chinese fluid sensor knockoff for a similar machine for this ink sensor that is a little 3 pin component that I can't identify and which has no markings on it. The chinese sensor spoofer does not work on my printer, and at present none exists for my model, hence why I'm trying to figure this out. The chinese sensor however does measure .35nF and has continuity between 2 of it's 3 pins only.

I noticed Epson has a patent (Seiko) for a fluid sensor around 2000 that uses capacitance. But I don't really know what I'm doing, I've got so many gaps in my electonics knowledge, I'm hoping someone might be able to pipe in and say, well, yeah if there's no continuity, and your measuring capacitance, then it's probably capacitance based in design? Anyone have any knowledge of capacitance based fluid sensors, like do I need to setup a little logic analyzer to see if they are sending a signal through this sensor?

Fluid volume is apparently determined by data written in memory to the IC elsewhere in the ink cartridge, so I'm guessing this is really about fluid presence, but then why use capacitance if so (if they are doing that). Or, is the fluid shorting out an open circuit, and in this state that I'm reading it, I might expect to see the fluid demonstrating capacitance? I keep seeing things on the web about capacitance based fluid LEVEL sensors, no for detection of presence of fluid only, that's why I ask.

Thanks and sorry for not being clear, I'm a bit over my head at this point, but steadfast and passionate about solving this and knowing a little more about the workings of this little smart ink cart.

Thanks in advance - David

[amyk]

The easy and pragmatic way to do it would be to cut the sensor out with some ink in it and then seal it off and connect it back to the rest of the circuitry.

[davidDac]

I was thinking about that too, hmm, it seemed to me though that I'd have to effective encapsulate the sensor chamber (about 2mm) square in such a way that the solvent in the ink wouldn't evaporate over time, which I guess I'd expect would change the ink's conductive or capacitive behavior?