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3.3V sensor to 5V ADC — Parallax Forums

3.3V sensor to 5V ADC

sciguysciguy Posts: 48
edited 2009-11-23 17:17 in General Discussion
Hi there!

This isn't specifically Basic Stamp Related, but I figured somebody here would be able to help.

I have some 3.3V sensors with analog outputs that I would like to interface to a 5V ADC converter, while maintaining full resolution. ie, I don't want to just give up the range of digital values generated between 3.3V an 5V. An example of one of these sensors is a 3 axis accelerometer, with an analog output for each axis. You can view the data sheet here: pdf1.alldatasheet.com/datasheet-pdf/view/103487/MOTOROLA/MMA7260Q.html

The ADC expects a value between 0 and 5V volts (analog), so if I just send in the 3.3Vmax signal, I'll be wasting valuable resolution. How can I proportionally amplify the 3.3V sensor output so it ranges from 0 to 5V?

Thanks so much!!!

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I can haz propeller chip?

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2009-11-23 04:59
    You don't need to amplify.· The ADC runs off one voltage and its reference can be a different voltage (it doesn't have to be V_cc.)
  • sciguysciguy Posts: 48
    edited 2009-11-23 05:03
    The ADC is built into this board. I've ordered it, but I can't really work out how it works until it gets here:
    http://www.trossenrobotics.com/p/Bioloid-IO-Board.aspx

    However, there is a 5V regulator that powers the sensors, which could easily be replaced with a 3.3V regulator. perhaps I'll get lucky and that reg is hooked up to the reference on the ADC as well. If not, looks like I'll be cutting some traces...

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    I can haz propeller chip?
  • FranklinFranklin Posts: 4,747
    edited 2009-11-23 05:26
    What do you plan to hook this to? Like you said, you will have to wait until you get it or find the datasheet for this device.

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    - Stephen
  • sciguysciguy Posts: 48
    edited 2009-11-23 05:27
    The link is above. It's not very well documented, so I'll have to trace things out when I get it...

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    I can haz propeller chip?
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2009-11-23 15:14
    That Bioloid I/O board doesn't have an ADC, it's a atmel or pic or whatever programmed for analog inputs and there's no reference/scale voltage as with a true ADC.· There was no documentation·available on the website.

    You are correct, this Subject doesn't belong in this area at all.
  • sciguysciguy Posts: 48
    edited 2009-11-23 15:30
    In that case, can you think of any way for me a scale a 0-3.3V signal up to 0-5V?

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    I can haz propeller chip?
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2009-11-23 15:36
    Make a Non-inverting amplifier, X1.5 gain.
    Look for a datasheet for an LM358, it's a dual op-amp designed for use with single-ended (+V and GND) supply.
  • sciguysciguy Posts: 48
    edited 2009-11-23 15:50
    thanks [noparse]:)[/noparse]

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    I can haz propeller chip?
  • dandreaedandreae Posts: 1,375
    edited 2009-11-23 16:40
    This thread is being moved to the "Sandbox"

    Dave

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    Dave Andreae

    Parallax Tech Support·
  • sciguysciguy Posts: 48
    edited 2009-11-23 17:17
    Thanks for moving. By the way, I spoke to the developer of the board, and it turns out that the regulator is being used for both power to the sensors and the reference for the ADC, so I can just swap it to 3.3V.

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    I can haz propeller chip?
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