How to send 4-20mA (1/3000 resolution)

BronsonBronson Posts: 44
edited August 2010 in BASIC Stamp Vote Up0Vote Down
Hi,

I am doing a project using BS2 that need to send 4-20mA signal (1/3000 resolution).

The workflow is: After BS2 receiving input through RS-232 (ASCII), it will send 4-20mA signal.

I have no problem receiving ASCII data through RS232 and process the ASCII with BS2, but I have zero-knowledge about sending 4-20mA using BS2.

By browsing this forum, I found that I need DAC (16-bit for 1/3000 resolution). Can I use MAX5661? How to do the wiring between MAX5661 (or any 16-bit DAC) and BS2? How to do the BS2 code?

Pls help me.....Thx a lot

Bronson Alex
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Comments

  • 8 Comments sorted by Date Added Votes
  • BronsonBronson Posts: 44
    edited August 2010 Vote Up0Vote Down
    Is AD421 (DAC 12-bit Serial-interface) suitable for BS2?
  • PJAllenPJAllen Banned Posts: 5,065
    edited August 2010 Vote Up0Vote Down
    Here's a recent Subject that dealt with 4-20mA:
    http://forums.parallax.com/showthread.php?t=120302&highlight=20mA

    Unfortunately, the ascii-art didn't exactly translate with the Forum's migration to its present format (if you copy and paste it into Notepad, it'll probably come right, with Lucida Console.) When it comes to pics I always post Dwgs, text is for text.

    For the DAC'ing, go to the Parallax http://www.parallax.com store site and search for DAC. You'll find links to sample programs, etc., which should provide clues for you if not for your specific device.
  • PJAllenPJAllen Banned Posts: 5,065
    edited August 2010 Vote Up0Vote Down
    Attached is a dwg for a current source (regulator.)
    It's not ascii-art, but it'll have to do.
    377 x 317 - 51K
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 20,116
    edited August 2010 Vote Up0Vote Down
    The AD421 should work fine with the BS2. Since it's a loop-powered transmitter, you could even use it with digital isolators between it and the Stamp.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. –Antoine de Saint-Exupery
  • BronsonBronson Posts: 44
    edited August 2010 Vote Up0Vote Down
    Phil, Could you pls send me the wiring diagram for using AD421?

    Thx
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 20,116
    edited August 2010 Vote Up0Vote Down
    I don't have a wiring diagram. The AD421 datasheet includes the information you need. Aslo, there's a schematic on this page that shows the AD421 connected to a PIC. The connection would be similar for a BASIC Stamp.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. –Antoine de Saint-Exupery
  • BronsonBronson Posts: 44
    edited August 2010 Vote Up0Vote Down
    Thanks Phil...
    I will try your suiggestion right away.
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