Hey Guys, I've been following this forum for a few weeks now and have a few things to add:

Firstly I think it is a great idea to have a secondary validation of Z height. I've heard the Kalman filter come up a lot in positional robotics, and it sounds very interesting.

As for sensing the Z height, I think that the suggestion of using a strip of foil on the side of the top reservoir is absolutely brilliant. I would likely use copper foil as it is easy to solder wires to, and comes in standardized thin tape rolls.

This would only work with relatively thin dielectric walled containers, and would likely need a calibration step. You would also need to have another wire inside the reservoir to complete the circuit. Once calibrated, the capacitance should be linear with salt water height.

I don't know what the Peachy uses for electronics, but the way I would implement this is to use a 555 timer as a capacitance meter, and then send the square wave signal to the computer. Audio works best since you can just pulse modulate your drip received signal so every droplet interrupts the current state of the Z height. Imagine two people, one constantly expressing their detailed undying love towards the current height of the reservoir, and another impulsive and insensitive colleague occasionally interrupting them to announce when a droplet has been received.

Schematic: http://www.eleccircuit.com/simple-ca...-using-ic-555/
(One of many out there)

I would go for the newer 2MHz capable 555's since the capacitance may be in the pF range.



Regarding drips and droplets:

I worked for four years in a chem lab before engineering, and we used Pasteur Pipettes to dispense droplets for assays. They are thin glass tapered tubes that produce consistent droplets (apparently (I hope since I used them a lot!)) and would have a tiny bulb at the end. They would be sold very cheap sans-bulb and could be a better option than what is currently being used. (By simply connecting them to the rubber tubing)

The other detail about the drip I am fuzzy on is that long thin tube which transmits the droplets to the reservoir below... wouldn't it be more consistent to have a big tube with the droplets falling straight down into the salt water?


That's all I got!

I really really really hope this peachy printer thing works out... good luck guys and gals!


-UD