Many coffee-brew stations drip the just-made coffee into a glass vessel that sits on an electric heater. Gradually the water in any un-drunk coffee evaporates, and eventually it dries, burns, and stenches up the surroundings awfully.
So, consider those low-power laser pointers -- let us build one into the brewing device. The beam is aimed at an angle downwards through the top of the glass vessel, so that it exits the glass near the base of the vessel. A sensor built into the brew-station at that point can detect the beam. However, if the vessel has a decent amount of coffee in it, it blocks the beam. Only when the coffee level drops so it no longer blocks the laser, can the sensor detect it. This causes the brew-station to shut off the electric heater under the vessel.
(NOTE: I did look around the HalfBakery for something like this idea, but didn't find anything. Perhaps something similar has been getting marketed for years already, but I'm not a coffee drinker, so never needed to find out -- and burned coffee has happened often enough at my workplace that if they WERE marketed, we'd probably have one there!)-- Vernon, Sep 01 2004 Auto Shut-Off Coffee Maker: http://www.halfbake...ff_20Coffee_20MakerThis one goes by weight. I just discovered this "old-fashioned" view, and it's cool (also PDA-friendly). [Amos Kito, Oct 04 2004] Refraction of Light http://ww2010.atmos.../mch/refr/less.rxmlThis is how a straight laser beam can miss a sensor, if clear water is in the way. [Vernon, Oct 04 2004] good, concise, I understand it, hey who are you really!-- dentworth, Sep 01 2004 What if you leave the full coffee maker on, and it boils down to a thick crust? Not that I’ve ever done that, of course…
Some random thoughts:This requires a transparent pot, and the pot, laser, and sensor must be kept clean. You can’t make hot water or weak coffee (without an override switch, which you must remember to set back to Auto). Steam will be a problem, since diffraction could cause the thing to shut off. You need a pot sensor as well, so the burner doesn’t turn off when you pour coffee. You can use an ordinary light rather than a laser, to operate the sensor... I wonder if there’s a spare LED in the hb?-- Amos Kito, Sep 01 2004 Or a float valve even.-- Etymon, Sep 01 2004 [Amos Kito], regarding the thick crust, I was intending the laser to be able to reach the sensor before the level of coffee in the pot got that low. "Near the base of the vessel", I wrote. I think if the beam exits at about half-a-centimeter above the bottom, that will suffice.
The transparent pot is pretty normally available. "Glass vessel", I wrote. Since the laser is aimed downward, its location is one that does not normally acquire dirt. The lower sensor, of course, does need to be clean; I figure if built into the smooth surface of the brewer, then any effort to clean the unit will automatically keep the sensor clear. Cleaning the glass vessel is likely already a regular chore, so, you aren't really raising any big issue there.
You CAN MAKE hot water or weak coffee; and they will actually ALSO interfere with the laser, as I'll describe a little later. You don't need a pot sensor, because the task of pouring coffee takes too little time to worry about the burner being shut off -- the heater will not have cooled much before the pot is replaced on the burner. Indeed, having the burner off when no pot is there may qualify as a safety feature!
You can use ordinary light EXCEPT that ordinary ambient room light will not be blocked by the pot, and that is why I chose a laser -- even low-power lasers are VERY bright, and a sensor that expects to see that much light will probably be able to tell the difference if the beam passes through weak coffee. However, that level of discrimination is not needed, because of "refraction". When a beam of light enters water at an angle, its path is bent. That means even a pot of clear water will prevent the laser beam from directly reaching the sensor!-- Vernon, Sep 02 2004 What about reflecting a laser off the surface of the coffee like a laser range finder to detect the actual level? Dunno how much laser energy is reflected off the surface of a liquid, but maybe enough to do the job? Infrared laser to cut through the steam?
Might be tricky to place the laser/detector perpendicular to the plane of the liquid, though. I guess it could attach to the bottom of or on a stationary mount below the filter basket.
Just thinking out loud...-- half, Sep 02 2004 [vernon] You are obviously suffering from caffeine deprivation....-- ConsulFlaminicus, Sep 02 2004 [half], I specified "at an angle downward". You don't get that useful refraction effect if the beam goes straight down.
[ConsulFlaminicus], I don't feel deprived at all, of caffeine. I LIKE avoiding the cost of the stuff.-- Vernon, Sep 02 2004 I have read every word of some of your ideas, and I would have bet that you were a coffee drinker, mainly because of how long I immagined that you stayed up to type them.<off topic> The old view in Amos's link is really something. I anno'd wondering if it would show up on that view and it does, but when you click on the idea in recent it comes up in the new format. Eerie.-- 2 fries shy of a happy meal, Sep 02 2004 Yeah, I read that. I didn't really have a problem understanding why you specified the downward angle and wasn't disputing it.
I was writing about reflection, not refraction in order to suggest a possible non-invasive, non-mechanical level detection method in lieu of a binary "got coffee"/"ain't got coffee" detection. (hence the use of the term "laser range finder") Probably wouldn't work great as the surface would be moving for a while after the pot is replaced or is filling. Maybe ultrasonic range finding could average out the distance to the surface better than a pinpoint laser.
The whole story is that I was thinking that actual level detection would enable what you proposed but would also add functionality for a networked coffee pot sort of thing.
I can't stand the stuff so I don't generally involve myself with coffee doings.-- half, Sep 02 2004 random, halfbakery