Posted Thu Aug 23, 2012, 7:35pm Subject: Re: Water level sensing circuit
Hi Bill
There was also a QT114-DG, but I wouldn't be surprised if you contacted the Quantum Research Group or Atmel that they might be able to assist:
North America 651 Holiday Drive Bldg. 5 / 300 Pittsburgh, PA 15220 USA Tel: 412-391-7367 Fax: 412-291-1015
or Atmel Corp
Atmel Corporate Headquarters 1600 Technology Drive San Jose, California 95110 United States Phone: 408-441-0311 Web: http://www.atmel.com/
They might be able to recommend an IC with similar properties that you could use. I remember when I was working on the circuit, that the real challenge, given the metal enclosure that the circuit sits in (i.e., inside the espresso machine) and the proximity to the boiler and other electrical interferences, was finding the right balance between the reference and measurement capacitance. At one point, any time I came within 5 feet of Sylvia, the LCD told me to "Add H2O"! Eventually, I got it right! Also, at least with the QT113, the ambient temperature inside Sylvia's case was not a problem.
TRUgEEk Senior Member Joined: 6 Aug 2012 Posts: 20 Location: east coast Expertise: I love coffee
Posted Thu Aug 23, 2012, 9:02pm Subject: Re: Water level sensing circuit
You could use two probes, one for low level and one for full. YMMV!
Thanks Wayne. I think that's a great approach, but I don't want to fool around with adding another port on the boiler at this point. I will probably do that once I build my own tank :-)
TRUgEEk Senior Member Joined: 6 Aug 2012 Posts: 20 Location: east coast Expertise: I love coffee
Posted Thu Aug 23, 2012, 9:08pm Subject: Re: Water level sensing circuit
Thanks Rick. I did a rough calculation and the capacitance change is probably on the order of a few picoFarads. I'm not sure it's worth the effort to get this working versus just a couple of simple probes as Wayne suggested. The main attraction is that the simple probe approach is prone to accumlating scale due to the DC. I may try and come up with a simple AC scheme that just uses a high and low level.
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