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digital thermometer help

Discussion in 'Electronic Design' started by [email protected], Apr 10, 2006.

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  1. Guest

    Here's what I'm looking to build.......hopefully someone has some good
    advice or maybe even has already built something similar.

    I've build circuits to detect temperatures in the past but I'd like to
    take it to the next level. I want to build a small, inexpensive
    circuit that will detect ambient air temperature changes, display temps
    to a small digital display, and even better, somehow log temp data (per
    second or so). My initial thoughts are to use a usb flash drive since
    they are small, inexpensive, and easily used with a desktop PC for
    later analysis of the temp data. Basically I want to place the
    thermometer at a location, leave, have the temp data logged, and be
    able to later review the temp data on a computer.

    Anyone have any advice on this one?

    Thanks!!!

    Steve
     
  2. You'll need a fairly powerful (micro)computer to talk directly to a
    USB peripheral. You might do better with a CF or SD card.
     
  3. Ian Stirling

    Ian Stirling Guest

    Define small, define inexpensive, and how long do you want it to log
    for?

    As a quick hack, I'd be looking at a MP3 player, with external RAM.


    Encode the sound in some form that the MP3 player can read.
     
  4. Tim Wescott

    Tim Wescott Guest

    Or include some flash in the thermometer and make _it_ a USB peripheral.
    USB masters are hard to make, but slaves are fairly easy if you don't
    try to cross every 't' and dot every 'i' in the plug & pray mechanism.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/
     
  5. Ian Stirling

    Ian Stirling Guest

    Or if you just pretend to be a serial/parallel port, and use one of the
    canned chips, which present an 8 bit 'friendly' bus.
     
  6. Guest

    My definition of small would be handheld size. Inexpensive is because
    I'll want to make like 5 of these, and hopefully it could log data for
    2 hours or so, 1 hour minimum. I'm sure there's a way to make an
    electronic thermometer (I remember doing it in electronics class) but
    getting it to work with some sort of data logger is my big problem. I
    guess I'd like to see any circuit diagrams others might have come up
    with if they are willing to share.

    Thanks

    Steve
     
  7. Omega has data loggers just as you describe. I believe under $100.

    Cheers
     
  8. artie

    artie Guest

    Take a look at http://www.onsetcomp.com/index_ppc1.html

    Hobo data loggers. USB or serial.
     
  9. xray

    xray Guest

    From the web page...
    GENERAL SPECIFICATIONS
    Measurement Capacity: 7943 readings

    I wonder how that number came to be? 1f07 in hex doesn't help my
    understanding.
     
  10. Ian Stirling

    Ian Stirling Guest

    Ok.
    What I would do, if I wanted to put one together quickly.
    As it's only 2 hours, the storage problem is simplified.
    Go to ftdichip.com, and find the link to the parallel 8 bit bus output
    ones.
    Now, two ways.
    A) Take a small PIC, and a temperature measurement chip - maybe one of
    the 'one wire bus' ones from TI, maybe not. Add an I2C LCD if you want,
    and a I2C eeprom chip. Accumulate samples at the specified rate until
    you can squirt them out the PC connected bus on demand.
    B) Take a 16 bit counter, a oscillator to clock data into the RAM, a
    32K*8 SRAM (62256), an 8 bit ADC, a suitable temperature probe (lm10?),
    and again hook it to the ftdi chip, with some glue logic. When you turn on
    the 'log' switch, it clocks the counter, samples the temperature, and
    writes to the RAM.
    When you plug it in, it resets the counter, and reads from the RAM on
    demand from the USB port.
    You add another gate or two, and it writes to the USB port too, enabling
    you to wipe the memory to 0.
     
  11. My Cricket Thermostat could be modifed as a logger. Just use the I2C
    temperature sensor and add an 24LC256 eeprom.

    www.myblueroom.com

    Bill
     
  12. My Cricket Thermostat could be modifed as a logger. Just use the I2C
    temperature sensor and add an 24LC256 eeprom.

    www.myblueroom.com

    Bill
     
  13. My Cricket Thermostat could be modifed as a logger. Just use the I2C
    temperature sensor and add an 24LC256 eeprom.

    www.myblueroom.com

    Bill
     
  14. Probably 8K less some overhead for calibration parameters etc.
     
  15. GregS

    GregS Guest

    My Fluke 189 has a variable width storage all depending on
    rate of change.

    greg
     
  16. Michael

    Michael Guest


    Take a look at: http://www.ubasics.com/adam/pic/picprog.html
    Its a PIC (sorta) tutorial and a temperature-logging project I found some time
    ago. Project uses a PIC16F84, 24C65 8-pin serial EEPROMs, and a DalSemi 1-wire
    temperature sensor. This project inspired the design of my own temperature
    logger. (I used PIC16F628 and 8 ea. 24LC256 EEPROMS though.)

    IIRC, your temperature sampling is to be 1/sec. That might be too frequent to
    implement with a 1-wire sensor, taking its conversion time, all software
    overhead, and EEPROM write time into account. The DS1822, for example, takes
    750 ms (max.) to do a conversion. My logger samples only once every 5 minutes,
    so I didn't have to consider conversion time, software overhead, or EEPROM write
    time in my design.
     
  17. Since you're using I2C eeproms it might be more efficent to use an I2C
    temperature sensor and larger EEPROMs 24lc1024.
    Only 2 I/O pins too.
     
  18. Since you're using I2C eeproms it might be more efficent to use an I2C
    temperature sensor and larger EEPROMs 24lc1024.
    Only 2 I/O pins too.

    See my PIC projects at http://www.myblueroom.com
     
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