I am trying to design an automatic water filling system for my coffee machine. I need to design and make two non-contact non-immersion level sensors for the water tank. Ideally these should use electrodes on a thin printed circuit mounted just behind the tank. It needs to detect two levels:

1. A low level "turn the water on" sensor
2. A high level "turn the water off" sensor

What is the best shape to make these electrodes?

where green is earth, red is live. Or something else.
I have not determined what circuit to use for the detector yet. I have a schematic for a RC oscillator design. But if you have a better idea, please describe.

Thank you - Rowan

 

... two non-contact non-immersion level sensors...

How are you thinking either configuration can sense the water level without being immersed? An optical or ultrasonic sensor might be better. A float switch is effective but I can see why you'd prefer no moving parts for this application. You may want to also consider a secondary, backup system to prevent overfilling. Failing to fill properly after going empty is a nuisance, but a runaway fill is a lawsuit.

 

How are you thinking either configuration can sense the water level without being immersed? An optical or ultrasonic sensor might be better. A float switch is effective but I can see why you'd prefer no moving parts for this application. You may want to also consider a secondary, backup system to prevent overfilling. Failing to fill properly after going empty is a nuisance, but a runaway fill is a lawsuit.

This TI app note might be worth skimming.

 

This TI app note might be worth skimming.

Well how about that. Learn something every day.

 

I've long used 300 ohm TV twin flat ribbon to make make tank depth sensors. Immersed but insulated from the liquid, measuring the capacitance change as the liquid level changes.

 

Well how about that. Learn something every day.

Yes, I found it very interesting. There are a lot of point level sensors available cheap as well.