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internal oscillatorthermometer — Parallax Forums

internal oscillatorthermometer

BADHABITBADHABIT Posts: 138
edited 2009-06-01 03:01 in Propeller 1
Is it possible to get temp readings bytaking a baseline measurement of the internal osc and measuring its variation during operation?

BH skull.gif

Post Edited (BADHABIT) : 6/1/2009 2:23:33 AM GMT

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-05-31 23:06
    There's no way to read the internal oscillator without using it for timing in which case you have no standard to compare against.

    The LM73 (and the LM75) is a nice little thermometer that uses I2C for its interface. You could attach this to the same I/O pins used for the EEPROM as long as you have pullups on both SCL and SDA. Any of the existing I2C drivers could be used to access it.
  • BADHABITBADHABIT Posts: 138
    edited 2009-05-31 23:41
    I was thinking about using it as internal temp gauge in a case that would use a higher than recomended clk speed. If an external temp regulated clk was used to for a comparison is it something that sounds feasible or is it kind of stupid.
  • Mike GreenMike Green Posts: 23,101
    edited 2009-06-01 00:07
    You should read the Propeller Datasheet. There has already been extensive testing and there are graphs showing the maximum reliable clock speed for various ambient temperatures and supply voltages. The Propeller will operate at higher than recommended clock speeds, but over a restricted range of ambient temperatures and supply voltages. Considering that a Propeller can be damaged with too high a supply voltage, you will need more careful design and better voltage regulation to operate closer to the margins. Similarly, you will need careful control of local temperature (around the chip) to run faster.
  • hinvhinv Posts: 1,255
    edited 2009-06-01 01:49
    Hi Mike,
    Could you hang an extern R and C on a pin and count the ticks in a crystal clock, and then switch to intern RCslow and RC fast and measure them compared to the Crystal.

    BADHABIT
    You couldn't test the temperature very accurately with an external RC because it would vary also. Which brings us back to another question. How do you "ring" a crystal with propeller pins.

    Thanks,
    Doug
  • hinvhinv Posts: 1,255
    edited 2009-06-01 03:01
    Actually, you could use a rtc like a DS1302 because it would have a 32768Hz crystal on it.
    Counting it's ticks and comparing them to cnt could give you the frequency of the RC clock you are running on(rcfast or rcslow) .
    Then you could experimentally subject your propeller to the whole range of temperatures and come up with a graph of temp/clock.
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