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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:
A low level “turn the water on” sensor
A high level “turn the water off” sensor
What is the best shape to make these electrodes?
where green is ground, 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.
Seems like I’ve seen moisture sensors using capacitive sensing, which is maybe what you mean by the RC oscillator. I probably wouldn’t want to pass actual current from positive to ground through the water if that’s what you’re proposing (Maybe it would work, and maybe that is an accepted technique, but just my gut feeling).
For more info on capacitive sensing, you might check out this article I wrote some time ago about ATtiny touch sensing: https://embeddedcomputing.com/technology/software-and-os/ides-application-programming/attiny85-capacitive-touch-sensing-sans-external-resistors – The other thing that could be very useful shapes-wise IIRC is this Microchip capacitve Touch Sensor Guide (referenced there): https://ww1.microchip.com/downloads/aemDocuments/documents/TXFG/ApplicationNotes/ApplicationNotes/Capacitive-Touch-Sensor-Design-Guide-DS00002934-B.pdf – Has been a while since I looked at it, but lots of great info IIRC.
Thanks for the suggestion! Capacitive sensing is exactly what I had in mind. I’ll take a look at your article and the Microchip guide you mentioned. those sound really helpful. I was thinking about using interdigitated electrodes to improve sensitivity. do you think that’s a good choice for this? Also, I’ve been considering an RC oscillator circuit for the detection, but I’m open to better ideas if you have any thoughts on that!
Glad I could (hopefully) help. I’m not sure what interdigitated electrodes are, so I have no input there. Oscillator may work well, but you could also look at doing the operation in firmware via a microcontroller.
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