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Beyond education

Jeff_BledsoeJeff_Bledsoe Posts: 10
edited 2007-10-24 15:57 in General Discussion
I bought a basic stamp kit a few months ago to try and upgrade one of the old BUNN 5-warmer coffee makers as part of teaching a high school class on programming.· The project has been on hold due to other priorities.

Can anyone pass along their·experience·applying·BASIC STAMP·in a high-temp and potentially moist environment?· The ideal water temperature for making coffee is supposed to be ~175 F.

Thanks,

Jeff

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Jeffrey Bledsoe, PE

jpbledsoe@yahoo.com

Comments

  • rePeterePete Posts: 18
    edited 2007-10-21 20:19
    Jeff,

    Not sure about the potentially moist environment part but I've used the stamp to control temperature. I used the stamp thermocouple module which made life pretty easy. Controlled a coffee roaster with temperatures past 470 F - everything performs like a champ - easy to attach a display as well. http://forums.parallax.com/forums/default.aspx?f=21&m=182223

    There is a solder pot temperature contoller which might give you some ideas as well with an interface.
    http://forums.parallax.com/forums/default.aspx?f=21&p=1&m=176959

    I always thought coffee wanted to be extracted at closer to 200 F but maybe that is one of those things where you get a different answer depending on who you ask.

    -Pete
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2007-10-22 16:33
    The 175F may be safer serving temerature. McDonadls was sued several times for serving coffee so hot that it was dangerous to elderly and the inattentive. I believe that 212F is ideal for brewing, but a clean pot is by far the most important factor for great coffee.

    Electicity and moisture general don't mix. And since coffee has an acid ph, it could actually leach lead from solder. While it is unlikely to be enough to cause harm and 5 volts is not a real hazard, it would be best to have the electronics in a tight enclosure. After all, there are always spills and overflows to consider.

    I suspect the BasicStamp will work right up to the temperature that causes the ICs to fall off it due to molten solder. Usually, the voltage regulator is the first to come off as it is easier to thermally abuse.

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    PLEASE CONSIDER the following:

    Do you want a quickly operational black box solution or the knowledge included therein?······
    ···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • Jeff_BledsoeJeff_Bledsoe Posts: 10
    edited 2007-10-22 23:52
    A friend of mine has a son who works at Starbucks and he was told they brew at 175 F.· However, in order to get 175 F at the basket, I might need to regulate at ~ 200 F in the tank.· An alternative would be to add another temp sensor right at the point where water exits the tube and falls into the basket.· Once the brewing starts, I could control the heater based on the exit temp.· Hopefully, the delay in water flow to the outlet wold cause excessive temp ringing. That's going a little too far with it.

    I prefer the simple way...one sensor on top of the tank (or inside the upper end of the tank) and setting the regulation point a little higher than the temp I want to achieve at the basket; some experiments could give me an idea how much higher.· I'd also add a high temp click thermostat as safety in case the controller gets stuck in the 'on' mode.· I plan to use an optically isolated·triac for power switching.

    Unlike the old Bunn analog controls which kept the tank hot 24/7, the microcontroller could shut down the standby tank heater after no brewing has been initiated for some (2 hours, e.g.) period of time...thus saving energy.

    I was considering mounting the controller/display·in an external box, connected to the maker with·power and signal wiring,·to get it away from the harsh internal environment.· (The old analog controls I removed show signs of heat/moisture stresses after ~20 years of service.)· Even if I mounted the controls internally, I'd enclose·them in a box of some kind.· The display, if mounted on the front surface of the maker, would be in a very harsh temp environment; perhaps I could·mount·it high-and-on-the-backside of·the maker, out of the path of hot air·rising from the basket.·

    The lead from the solder is something I hadn't considered.· I'll bet government regs require lead-free solder for all appliances·these days.· Of course, anything I do to the unit makes the UL seal null and void but it would be a good·platform·on which·kids·could demonstrate their code.

    I seldom post on Parallax so I don't know if I'm replying to only one or both of you....I couldn't see an option to reply to either one specifically.· Anyway, thanks to both of you for your advice and I'll check out the links in the post.

    Jeff

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    Jeffrey Bledsoe, PE

    jpbledsoe@yahoo.com
  • WhitWhit Posts: 4,191
    edited 2007-10-23 00:53
    There is also this for more hazardous environments...

    http://www.parallax.com/detail.asp?product_id=30064· smilewinkgrin.gif

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    Whit+


    "We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
  • pwillardpwillard Posts: 321
    edited 2007-10-23 03:43
    Would covering the NON-PIN sections of the STAMP (or if permanent, the whole stamp and board) with some kind of conformal coating be a good idea?

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    There's nothing like a new idea and a warm soldering iron.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2007-10-23 17:34
    Forgive me, but all the new Stamps are lead free, ROHS compliant. Still, electricity and water don't mix. When metal oxides, the layer of oxide creates unwelcome electrical resistance.

    We all work with unenclosed breadboards as a temporary basis, but any enclosure [noparse][[/noparse]even a clear Tupperware box] will enable you avoid funkiness. I live in a major steel making area of Taiwan and the acidity of the air is quite high - just leaving printed circuit boards out for a few months causes them to get dull and oxidized. I've seen 2 and 3 year old computer chassis that have turned to rust in places.

    There are some sprays that coat the board with a thin protective layer. Try an electronics supply house.

    You could 'pot' the circuit in something. Traditionally, devices were embedded in clear epoxy, but you cannot easily go back in for repair or changes. There are other softer resins, like silicon gel that is used for window and bathroom caulk.

    I 'pot' the backsides of circuit boards in hot glue in order to avoid shorts when they are on the bench. Hot glue can be easily cut out and removed with a utility knife, but offers good protection in most cases. I've had very pleasant rework experiences with it where I've had to cut out a section and do some further soldering. Then I recovered it with hot glue.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    PLEASE CONSIDER the following:

    Do you want a quickly operational black box solution or the knowledge included therein?······
    ···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • Dave HeinDave Hein Posts: 6,347
    edited 2007-10-23 18:52
    I've never designed a coffee pot controller before, but I have built some circuits that ran hot enough to boil water! cool.gif

    I did own a coffee maker with a clock that could be set to make coffee in the morning just before I got up. It had a valve between the pot and the basket that holds the coffee grounds. Once in a while this valve would stick in the closed position and the basket would overflow and spill several cups of coffee onto the kitchen counter. That's one way to quickly wake up in the morning!

    Some of the spilled coffee would leak into the circuit area. First the clock display would quit working, and then the coffee maker would shut off entirely. I would have to wait for the thing to dry out completely before it would work again. I got rid off that coffee maker a long time ago.

    So I would suggest that you completely seal the stamp and other circuitry so that it is air tight. The circuitry should also be thermally isolated from the coffee maker. It's OK if it 10 or 20 degrees above room tempurature, but you don't want it as hot as the coffee.

    Dave
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2007-10-24 15:57
    Well....
    As long as you are into proper thermal control, please take a look at my 'pregnant guppy' gel cell that came to life today.· This happened in a mere 10-15 minutes of charging. I keep thinking I'll get a thermal sensor attached to the battery during charging· to shut down a SSR, but I just haven't yet built it.· Time to get busy about it.

    My next posting will either be in completed projects or·captioned 'pregnant guppy goes ballistic'.

    Any one want their bedroom splattered with hot acidic gel?·

    BTW, the 8 volt gel cell is terrific for BasicStamps.· The charger is okay, just no shut off.

    And, have you ever seen a cold water coffee brewer?· I used to go to a pub that had one, but the flavor was a bit 'special'.· I don't even like iced coffee.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    PLEASE CONSIDER the following:

    Do you want a quickly operational black box solution or the knowledge included therein?······
    ···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 10/24/2007 4:06:40 PM GMT
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