Re: 3vdc motor PWM problem

On 28 Sep 2006 20:01:16 -0700, "randomname"
<randomname12345@xxxxxxxxx> wrote:


---
That's not my approach at all. I don't use a drop sensor.

What I'm suggesting is an astable with a manual frequency control (a
rheostat) triggering a monostable with a fixed pulse width.

To understand how it would work, assume that drops are leaving the
tube at a rate of 10 per second, that the astable was astabling at
10Hz, and that the monostable was strobing the LEDs for 10ms every
100ms.

What would happen is that as the drops fell a new one would be in
exactly the same place whare the old one was 100ms ago, and when it
was illuminated by the strobe, the impression would be given that
the new drop was the old drop which was suspended in space.

Now, increase the frequency of the astable a little, and the strobe
will flash a little earlier, illuminating the drop a little earlier
than it did the last one, giving the impression that the drop was
climbing. Slow the astable down, and it'll look like the drop was
falling. Not just the one drop though, the entire column of drops
will be illuminated and they'll all move in unison.



--
John Fields
Professional Circuit Designer

John, that's what I've got already. A simply astable will do, with the
"up time" flashing the strobe, and the (adjustable) "downtime"
controlling the frequency of the strobes. No need for a monostable.

The problem is getting a steady drip rate, its damn near impossible as
far as I can tell. It either drips sporadically or turns into a god
damn stream, which really is starting to piss me off.

I think I'm going to need a drop sensor, but I feel like this is going
to take a lot more work, and even if I did make a drop sensor, theres
no way to get the drops to appear as if theyre moving. It would be
easy to get them to freeze (flash strobe whenever a drop leaves), but
constantly increasing the time period in which the strobe delays after
a drop is detected takes a computer of some sort.

I've acheived some amazing results when I manage to get a stable drip,
but right now it's just not happening.

---
This is interesting to me, so I'm going to build one. :-)

I'll use a drop detector (either reflective or transmissive IR, I'm
not sure which, yet) and white LEDs to strobe the drops, which I'll
probably leave clear right at first.

My goal will be to generate 1/4" diameter drops that fall through
12" with a new drop being generated every 16ms or so. That'll give
the appearance of a single drop suspended in the center of the "drop
zone" with a drop rising out of the catch basin, following the
center drop when the center drop appears to rise, or a drop
appearing at the top of the drop zone, following the center drop
when it appears to fall, all depending on the detect-to-strobe
delay.

I have a submersible fountain pump which can deliver about 1.5
liters per minute with a 12" head, so that's enough volume VS time
to generate the quantity of drops needed. It runs off the 120V
mains so I'm not going to mess around with PWM'ing it, I'll just
control the flow with a needle valve I had laying around waiting to
be put to use.

Anyway, that's the plan...



--
John Fields
Professional Circuit Designer
.

Relevant Pages

  • Re: 3vdc motor PWM problem
    ... I don't use a drop sensor. ... What I'm suggesting is an astable with a manual frequency control (a ... tube at a rate of 10 per second, that the astable was astabling at ... Now, increase the frequency of the astable a little, and the strobe ...
    (sci.electronics.basics)
  • Re: 3vdc motor PWM problem
    ... Once you've got a steady stream of drops going, you can illuminate ... will strobe the LEDs and freeze the image of the falling drops. ... the 2 wire sensor. ... tube at a rate of 10 per second, that the astable was astabling at ...
    (sci.electronics.basics)
  • Re: 3vdc motor PWM problem
    ... Once you've got a steady stream of drops going, you can illuminate ... will strobe the LEDs and freeze the image of the falling drops. ... When a drip is ready to leave the tube it conducts thru ... tube at a rate of 10 per second, that the astable was astabling at ...
    (sci.electronics.basics)