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A STAMP, A pump, and lots of patience.... — Parallax Forums

A STAMP, A pump, and lots of patience....

InteractivesInteractives Posts: 83
edited 2005-06-22 18:24 in BASIC Stamp
OK, so the whole pump thing has changed once again. for those of you unfamiliar with the trails and tribulations of the pump controlled STAMP input, I'll summarize: Ive tried many things, and many things have worked. And yet the only truth is change, so here I am. I'm now trying to accomplish a very simple task: pump goes up, triggers an input signal to STAMP, pump goes down, it triggers a different signal. I have in my hands two 12VDC micro fans, and when they spin, they induce about .006 volts. That’s a very small voltage, and I can’t get a reading on Amps or resistance. Any ideas on how I could get this wee voltage to trigger a logic signal to the STAMP? I promise this will be the last revision!turn.gif

Comments

  • Jon WilliamsJon Williams Posts: 6,491
    edited 2005-06-22 16:06
    You your're trying to get the Stamp to "see" when the fans are spinning? Instead of using the voltage output (which would require an amplifier), maybe you could put an IR LED (with a simple 555 modulator) on one side of the blades and a receiver on the other. Using the COUNT or PULSIN you could detect movement.

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    Jon Williams
    Applications Engineer, Parallax
  • InteractivesInteractives Posts: 83
    edited 2005-06-22 16:14
    Thats a good idea, and before, when the project was about detecting the speed of the fan, I had that exact set up working for me just fine. I was just hoping that since all I have to detect is any movement at all, despite of speed, that there would be some easier way.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-06-22 16:17
    She's already done that. Ok let me rephrase to see if I understand what exactly you are trying to do. You have created the IR/detector to gauge the speed of the fan (I assume you are still using this method), but that setup doesn't tell you which direction the fan is going, so you need to know whether the hand billow is being compressed or expanded. Am I correct in my understanding of your question, or are you trying to find another method altogether?
  • InteractivesInteractives Posts: 83
    edited 2005-06-22 16:22
    actually , its another method all togather, this time it two fans. There is an input port under the bellows, and a seperate exhaust port, so the air supplies are already seperated. One fan spins when I pull the bellow up, and the other spins when I push it down. It's actually a lot less complicated than the stuff I was working on before.
  • InteractivesInteractives Posts: 83
    edited 2005-06-22 16:26
    The IR thing worked perfectly with the COUNT command to determine the speed of the fan, but the project as a whole was confusing to people. You all should come visit Chicago in March to see some of these finished projects!
  • steve_bsteve_b Posts: 1,563
    edited 2005-06-22 16:40
    How much air do these fans move?
    Maybe a microswitch with a little foil sail to catch the moving air and trigger. As far as the direction....put one on both sides....the fan blades only let air flow in one direction.
    Another idea would be to use some temperature sensors. One in the front of each fan and one as a reference in teh enclosure. Then compare each fans' temp sensor with the reference to see if the wind is going across it and cooling it.

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    ·

    Steve
    http://ca.geocities.com/steve.brady@rogers.com/index.html
    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • InteractivesInteractives Posts: 83
    edited 2005-06-22 16:48
    Yes, I believe that would work as well. I went to the sensors expo 2 weeks ago, and actually got on a list for some samples of pressure sensors, temp. sensor, et cetera, but I havent gotten any yet. Jon mentioned that I would need an amp to use this analog signal- any of you know where I could get a schematic on making one of those bad boys? Or should I just go back to the shack?
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-06-22 16:48
    Ok, I understand now, sorry I thought it was the same project. The IR method is still the most robust method, other methods can be derived (using an analog comparator comes to mind) but 6 mV is very low voltage to compare against and you will likely run into problems such as offest error, not really a realm you want to get into. Ill place it in the back of my mind and see if anything percolates to the top. Can you access the inside of the bellow? Im thinking maybe even a simpler setup such as a leaf switch and a paddle attached to the end would provide a simpler interface (hence easier to understand). The air flow would push against the paddle causing the switch to close, but for the intake valve you should place the switch inside the bellow.
  • InteractivesInteractives Posts: 83
    edited 2005-06-22 16:55
    I can get inside the bellows, but from experience, kids seem to like breaking things. Theyre gonna go nuts on these things, so I'm very reluctant to put switches inside the bellow. With the fan set up, I think the fans will run ok, and we can replace the bellows at will, when they get destroyed. I am frightened by your description of offset error.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-06-22 17:07
    Ok a quick look at some analog comparators, it should be possible but you will need to get a precision one (the non-precision ones I looked at have offset voltages in the range 8mV, and cannot be used), the AD790 has an offset voltage of 250uV, low enough to be used. But they are $8.16 apeice @ digikey. Providing an accurate reference voltage will also be an issue since most voltage references are 1V and above, and scaling the voltage down with a resistor voltage divider introduces an error from the inaccuracies of the resistors used. You could try to use ground as your reference but 0V compared to 0V with a 250uV offset error (this is the situation when the fan is not spinning), you could end up with false triggering.
  • InteractivesInteractives Posts: 83
    edited 2005-06-22 17:14
    hmmm... so the simple solution becomes complex. O.k., maybe I'll just have to deal with the whole opto thing. The good news is: I already know how.(Mostly)
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-06-22 17:51
    Hello,

    ·· Jumping into this a little late, but it occurred to me that if the fans you're using are the little muffin fans, like ones used in computer cooling, they don't give any real good output voltage from being turned like a standard brush motor would.· Perhaps if you had a fan blade attached to a brush-type motor you would get a higher voltage which could be more easily read by the Stamp,·possibly without amplification.· Just a thought.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Lee HarkerLee Harker Posts: 104
    edited 2005-06-22 18:24
    By the description of the voltage you are getting from the fans, I'm guessing that they are the brushless dc variety. If that is the case, you will not get an output representative of the RPMs. They actually have a driver circuit in them and are a user of electricity only.
    Your idea of using a pressure sensor is probably the best way. I have used these before and they are pretty straight forward. You can find them in many configurations for around $20.00 from Digikey. They are preamplified so you would need only an A to D converter. You can set it up to measure differential pressure so you could tell whether the bellows was pulling air or pushing it.
    Lee
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