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controlling a continuous voltage via bs2 — Parallax Forums

controlling a continuous voltage via bs2

polrampolram Posts: 7
edited 2004-09-30 22:18 in BASIC Stamp
Hello Forum.

I would like to know if this is possibe via the bs2 stamp: Any suggestions would be greatly appreciated...

The requirement is for 2 inputs controlling a single, continuous output.

For example:

If a signal is given to input high via a momentary/manual switch at Vref,
then the voltage increases as long as the momentary switch is held. As soon
as the switch is released, that final voltage magnitude is maintained.

Now, if the signal is given to input low via the momentary/manual switch,
then the voltage decreases as long as the momentary switch is held. As soon
as the switch is released, that final voltage magnitude is maintained.

This final voltage magnitude needs to be "indefinite". Meaning, if I left it set at like 7VDC,
I can come back 2 weeks later and change those 7VDC.



How can I use the bs2 to help me keep this voltage maintained without degrading?

The minimum voltage range is +/- 10VDC.


Use the graph attached for operation reference.

Thank you so much,

Regards,

polram
GRAPH.JPG
640 x 512 - 13K

Comments

  • NewzedNewzed Posts: 2,503
    edited 2004-09-29 17:46
    Before anyone can help, we need to know how much current is being drawn - 1ma, 5ma, 50ms ???

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    Sid Weaver
    Try the Stamp Tester

    http://hometown.aol.com/newzed/index.html
    ·
  • Lee HarkerLee Harker Posts: 104
    edited 2004-09-29 20:55
    Polram,
    What you are asking for shouldn't be too hard. Here is one possibility. You would set up a counter on the Stamp and monitor the two switches for "up" and "down". When the Stamp detects that one of the switches is activated it would either increase or decrease the counter value accordingly. Each time the counter value is changed you would send the new value to a DAC. The DAC output would have to be conditioned with an op-amp to scale and offset it to realize a +-10V excursion.
    Now for the nitty gritty stuff. You will have to decide the resolution per change and pick the DAC accordingly. Also, the rate of change as the switch is held down will have to be considered. If the Stamp is running at full rpm, the entire range could be covered before you let go of the switch.
    You will need to a little math such that the minimum output from the DAC will be -10V and the maximum will represent +10V.
    By nature the value you set will stay there forever as long as power is applied. For extra measure, you could put the setting in EEPROM in case of a power failure.
    Hope this helps.

    Lee Harker
  • polrampolram Posts: 7
    edited 2004-09-29 20:57
    The current draw is no more than .5 Amps...
  • polrampolram Posts: 7
    edited 2004-09-29 21:00
    Thank you very much for the information, Lee. This certainly helps. I will investigate... Regards,

    polram
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2004-09-29 22:04
    You could use your button inputs to change a variable that would then be sent to the PWM instruction. The length of the PWM instruction would serve as the delay between button tests. You will need to buffer the PWM's RC circuit with an opamp to get a usable voltage.

    Here's an idea for the code:

    Set_Voltage:
    · DO
    ··· IF (level < 255) THEN········· ' check for max value
    ····· level = level + IncVolts
    ··· ENDIF
    ··· IF (level > 0) THEN
    ····· level = level - DecVolts···· ' check for min value
    ··· ENDIF
    · PWM PwmPin, level, 50
    · LOOP

    The (active-high) buttons get scanned and the output updated every 50 milliseconds.

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    Jon Williams
    Applications Engineer, Parallax
    Dallas Office
  • DaveGDaveG Posts: 84
    edited 2004-09-30 04:38
    Polram,
    If I may ask, what are you trying to drive with the +-10volts at 0.5 amps? And what
    resolution do you require?
    A linear output stage that can handle 0.5 amps will probably require a power op amp
    and some sort of heat sink.
    Dave G
  • polrampolram Posts: 7
    edited 2004-09-30 13:47
    Dave,

    This is en elctro-mechanical application, part of a bigger circuit. I do need to drive part of a motor assembly. Yes, you are correct, I will need to incorporate a power gain circuit.
  • polrampolram Posts: 7
    edited 2004-09-30 13:49
    Jon, thanks for the suggestion on the code.

    Here is another possibility I am investigating:

    How easy will it be turn the stamp into a 1Hz oscillator?

    P.
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2004-09-30 17:14
    Pretty easy...

    One_Hertz:
    · TOGGLE Outpin
    · PAUSE 500
    · GOTO One_Hertz

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    Jon Williams
    Applications Engineer, Parallax
    Dallas Office
  • allanlane5allanlane5 Posts: 3,815
    edited 2004-09-30 17:39
    Of course, you didn't say how ACCURATE a 1 Hz oscillator you wanted.

    I believe the BS2 will be accurate +- 10% or so -- which isn't very accurate, really.
  • polrampolram Posts: 7
    edited 2004-09-30 19:55
    Yes, +/- 10% is a little high. I was shooting for aout 2-3 %...
  • polrampolram Posts: 7
    edited 2004-09-30 19:57
    Thanks for the code, Jon. I will give this a try.
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2004-09-30 22:18
    Yes, do. I believe Allan is mistaken -- but I'm in the middle of a huge project now and don't have time to confirm. Here's fine-tuning tip:

    PAUSE 0

    will give you about 100 microsecond pause

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    Jon Williams
    Applications Engineer, Parallax
    Dallas Office
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