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Voltage and Amperes Check

Discussion in 'General Electronics Discussion' started by fuggles, Dec 14, 2009.

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  1. fuggles

    fuggles

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    Dec 14, 2009
    I am attempting at a project to create a controller that will adjust a fan via a given temperature. I would like to be able to plug this project into the wall(Standard American Voltage, 120VAC, 60Htz). Each of my power-consuming components and their voltage and current usages are in the attached file. Could someone help me on regulating the voltages/currents for each component(transformer, voltage regulator, controlling current, etc.)
     
  2. fuggles

    fuggles

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    Dec 14, 2009
    Sorry, I forgot to attach the file. ;D
     

    Attached Files:

  3. Resqueline

    Resqueline

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    Jul 31, 2009
    You can build the 5V supply yourself from a 7V ac 500mA wall-wart transformer, with the rectifier, 470uF cap, & 7805 regulator inside the project. Or a 9V dc 350mA wall-wart with the just 7805 in the project. But you can use the rectifier & cap with either wall-wart. Or you can just get a ready-made regulated 5V supply (some cell-phone chargers, USB supplies/chargers, etc.). If it says 5V you can use it.
    The LCD contrast usually consists of a simple variable resistor connected to two pins on the display. The values you posted suggests a 200 ohm resistor in series with a 133 ohm potentiometer. If uncertain please post the LCD make & model, or a link to the datasheet, if it's not a secret.
    Temperature 3V 2mA? I don't get that one.. Maybe it's a modern integrated temperature sensor that can only run on 3V? If so you'll need a modern 3V regulator. I'm sure many of them are surface mount. Is that an option?
     
    Last edited: Dec 16, 2009
  4. fuggles

    fuggles

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    Dec 14, 2009
    Just to make sure. HERE is the link to the LCD datasheet.

    And the temperature sensor is an analog thermistor. That is just the voltage I will be sending to it for my PIC to read. HERE is the link to the thermistor.
     
  5. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    Ok. The LCD simply wants a 10k to 20k potentiometer connected like on page 4 in the datasheet. Disregard the voltage statement about it there.
    I question your choice of that thermistor as the sensing unit however. It has an accuracy of +/- 20%, translating to 77 deg. F. You'll have to calibrate & linearize each one manually. I don't understand the 3V feed requirement for it either.
    Did you choose it for the small size & quick response? If not then there are many calibrated integrated sensors that interfaces much more easily with your PIC.
     
  6. fuggles

    fuggles

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    Dec 14, 2009
    I chose it for the high temperature rating and analogue output, as it will be put inside of a smoker and needs to be able to withstand high temperatures and preferable minimal amount of wires. Would you recommend another one to me?
     
  7. Resqueline

    Resqueline

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    Jul 31, 2009
    I see.. Yes, you'll be blue before you find a semiconductor that withstands the kind of temperatures it does. A platinum sensor is a more predictable alternative, but still you'll need a suitable interface and I can't tell you straight away how to go about it. Do you have any particular interface planned for the NTC, and do you plan to do the calibration & linearization in software? If so, how much resolution do you have to go on?
    Sorry for straying away from your initial question.
     
  8. fuggles

    fuggles

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    Dec 14, 2009
    Yes, I do plan to convert the voltage to a temperature in the software, and I would like to get within 10-20 degrees F.
     
  9. fuggles

    fuggles

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    Dec 14, 2009
    How does THIS one look?
     
  10. Resqueline

    Resqueline

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    Jul 31, 2009
    That one is 5% accurate so it'll be much more repeatable but you'll still have to use a lookup table or something to convert the voltage to a temperature. More than 8 bits will be needed.

    Linearizing an NTC can be accomplished by a suitable resistor in parallell with it, and then of course a suitable resistor in series with this.

    The supply for this can just as well be 5V afaik.

    How high can the temps get in that smoker btw.?
     
  11. fuggles

    fuggles

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    Dec 14, 2009
    I don't think its every been above 300-350 degrees Fahrenheit.
     
  12. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    Ok, you are reaching a critical point there. 300 is within the reach of many integrated temperature sensors (like the LM34 for instance) while 350 is approaching the melting temperature of solder.
    Some digital output sensors are actually two-wire devices also, and you wouldn't even need an a/d then.
    I believe the integrated sensors will survive short-term surges to 350 F.
     
  13. fuggles

    fuggles

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    Dec 14, 2009
    Yea, we usually cook meat at about 225 degrees anyway. But its surged up to about 300 before. Then again this device is built to regulate that.
     
  14. fuggles

    fuggles

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    Dec 14, 2009
    And how can you get digital output from a 2-wire device? Serial connection?
     
  15. Resqueline

    Resqueline

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    Jul 31, 2009
    Yes, it incorporates both power supply and serial data transfer on the same wire. (Much like an electret mike.)
    I just Googled "two wire digital temperature sensor" which brought info about them. I don't know their price, data, or availability though.
     
  16. fuggles

    fuggles

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    Dec 14, 2009
    Alright. I'll see what they have on Mouser. Its a very good site for ordering electronics components.
     
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