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ANALOGIN Problems — Parallax Forums

ANALOGIN Problems

MacGeek117MacGeek117 Posts: 747
edited 2006-10-17 15:39 in General Discussion
I just started·to work with the ANALOGIN command, and it works fine for Vdd and Vss(255, 0, respectively), but it doesn't work for any value in between(I have a voltage divider composed of two 10k resistors connected to Vdd and Vss). Could I please have some help?
RoboGeek

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Comments

  • BeanBean Posts: 8,129
    edited 2006-10-13 17:17
    You'll have to explain what "it doesn't work" means ???
    What value to you get ? What cap value are you using ?
    Details man, we need details...

    P.S. Are you setting the input pin to CMOS trigger level ?

    Bean.

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  • MacGeek117MacGeek117 Posts: 747
    edited 2006-10-13 17:49
    I am using the schematic and program out of the What's New readme file(I am posting both). When I use the divider the value bounces between 0 and 14, where it should be about 127.
    RoboGeek

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    txt
    txt
    Whats New.txt
    5K
    SXB
    SXB
    TEST7.SXB
    2K
  • BeanBean Posts: 8,129
    edited 2006-10-13 18:20
    Try using two 1K resistors to create your voltage. The 10K resistance may be too high.
    Does the voltage measure 2.5V on a meter ?
    Try a larger prime value.
    Double check your connections.

    Bean.

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  • MacGeek117MacGeek117 Posts: 747
    edited 2006-10-13 20:21
    I've tried the prime values up to 50. Circuit is fine. Input voltage is 2.495V. The ADC still says 0. I simply don't understand!
    RoboGeek

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  • BeanBean Posts: 8,129
    edited 2006-10-13 21:17
    Keep trying stuff, something not right. It DOES work. I have used it and others have too.
    Try using RB.0 & RB.1 like the example.

    Bean.

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  • MacGeek117MacGeek117 Posts: 747
    edited 2006-10-14 01:46
    Thanks for your help, Bean! I misread the cap value. It works now Thanks!!!!!!!
    RoboGeek

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    ·
  • BeanBean Posts: 8,129
    edited 2006-10-14 02:10
    Cool, I'm glad you got it working.
    Persistance pays...

    Bean.

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  • ellizardellizard Posts: 106
    edited 2006-10-17 10:46
    HI Everybody,

    Just for information,
    Where (apart on this forum's trhead) there are informations on the new command ANALOGIN?
    I searched in the help window and there's no mention of such a command,
    I searched also the What's new section of the SX basic and there's only
    What's New In SX/B 1.51.03
    New Commands:
    LOOP NEVER
    Changes:
    Changed HIGH & LOW if a pin, set state again AFTER making it an output
    Fixes:
    Fixed: Literal replacement didn't handle strings in quotes
    Fixed: name CON -5 compiles as name CON 5 said...


    This is all i could find about.
    Please more informations needed

    Regards
    Stefano

    Post Edited (ellizard) : 10/17/2006 10:51:03 AM GMT
  • BeanBean Posts: 8,129
    edited 2006-10-17 11:39
    Here is a link that explains how it works: http://www.sxlist.com/techref/scenix/lib/io/adc_vp.htm

      ANALOGIN InPin, OutPin, Value[noparse][[/noparse], Prime]

    Reads an analog input voltage using the continuous calibration method

 
    All you need is 2 10K resistors and a 0.01uF capacitor(for 4MHz) or 0.001(for 50MHz)

 
    You can experiment with different resistor and/or capacitor values. Don't use resistor
      values below 220 ohms to protect the SX output pin.
 
    The variable Value will get set to the analog voltage at the input with
      255 = Supply voltage. So if you get a reading of 127 and the supply voltage
      is 5 volts, then the input voltage is about 2.5 volts.
 
    Note that the input pin needs to be set to CMOS input threshold. By default
      the sx sets all pins to TTL threshold. The TTL theshold is 1.4Volts. That
      will make the full scale reading of 255 = 2.8 volts regardless of the
      supply voltage.
 
    The method needs to "prime" the capacitor to get a stable reading. By default
      the prime value is 1. If you get unstable readings either use a smaller cap value
      or increase the prime value. Prime must be a constant from 0 to 255. However
      larger prime values will increase the time it takes to get a reading.
 
    The time required to get a reading is 3825*(1+Prime)/Frequency. So with the
      default prime value of 1, if the clock is 4MHz it will take
      3825*2/4000000 seconds or about 1.91 milliseconds to get a reading.
 
    For faster clocks either use a smaller cap value or a larger prime value.
 
    Note that this circuit has a fairly low input impedence. If you use a pot or resistor
      divider to create the analog voltage the ANALOGIN command may not reach the 
      limits (0 or 255). A simple test using the 10K pots on the PDB yielded values
      from 0 to 241.
 
  The following is an example program:
'-------------------------------------------------------------------------------
DEVICE SX28, OSC4MHZ, TURBO, STACKX, OPTIONX
FREQ 4_000_000
InPin  PIN RA.0 INPUT CMOS
OutPin PIN RA.1 OUTPUT
' Analog Voltage >---/\/\/\-------+----+------------ SX Read Pin (RA.0)
'                      10K        |    |
'                               -----  +--/\/\/\---- SX Write Pin (RA.1)
'                               -----       10K
'                       0.01uF /     \
'                                 |
'                                 |
'                                GND
a VAR Byte
PROGRAM Start NOSTARTUP
Start:
  ANALOGIN InPin, OutPin, a, 2
  WATCH a
  BREAK
  GOTO Start
END

    You can also try looking in the help for the Javelin. It has a similar command. I thinks it's called "ADC" on the javelin.

    I hope this helps,

    Bean.

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    Cheap used 4-digit LED display with driver IC·www.hc4led.com

    Low power SD Data Logger www.sddatalogger.com
    SX-Video Display Modules www.sxvm.com

    Don't mistake experience for intelligence. And vis-vera.
    ·
  • ellizardellizard Posts: 106
    edited 2006-10-17 15:39
    thanks for the information so quick..........
    hope it will be in SX-Basic help window too.......

    it helped somehow

    Stefano
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