Re: 555 timer problem


default wrote:
On 26 Sep 2006 12:40:36 -0700, "randomname"
<randomname12345@xxxxxxxxx> wrote:

The motor is a tiny submersible 3vdc water pump. The problem is that
the frequency of the 555 timer will alternate. Ive hooked up a piezo
in parralel to the motor, so I can hear the frequency of the timer. (I
dont have an oscilloscope)

It will be high for a few seconds, then dip low for a few seconds, then
go back high. When this happens, it changes the RPMs of the motor
which changes the flow of water -- I need a constant flow of water. I
just need the motor to run steady at a certain rate, which it does, but
only for short bursts of time.

I need the 555 to stay as constant as possible... but for some reason
the 555 timer is giving me a hard time. Any suggestions? Thanks a
lot!

Maybe not what you are after, but if I were trying for a precise
amount, particularly individual drops of liquid, I'd look into
chemical metering pumps. I forget the name of the manufacturer, but
someone makes a tiny (Ice Cube size) solenoid pump that is capable of
very precise delivery with each stroke of the solenoid.

I saw the thing at a pharmaceutical instrument trade show. Vicor may
be the name of the company - but searching didn't turn up hits on a
pump. Slick little pump - they had it making precise timed air
bubbles and timed droplets of one fluid in another (immiscible) fluid
(like those wave tank thingees they sell to executives to put on their
desks, or the old lava lamp)

From what you are saying, I get the idea that you are dealing with a
centrifugal type (impeller) pump (similar to a car windshield washer,
or boat bilge pump). For precise delivery a positive displacement
pump will work much better - each revolution or stroke of a piston
delivers a known amount of fluid and if you stop up the outlet the
pump stalls.

And if that is the idea - no pressure necessary - you could just use
your pump to pump up a liquid to a small reservoir and let it overflow
to maintain a constant head - then regulating the drips could be done
with a small needle valve or pinch valve on some tubing. Motor speed
of the pump isn't critical to delivery rate that way.

One solution, with the pump you have, if you want pressurized water,
may be to use it to pressurize a bladder tank similar to what well
water systems use. Sounds farfetched; don't it? On a miniature
scale, a balloon in a plastic enclosure. The bladder is in a rigid
enclosure and water can inflate the balloon compressing the air around
it (to provide a method of storing the small amount of pressure).
Balloon mechanically/magnetically opens a switch and shuts down the
pump until the pressure drops a little (or operates a linear
potentiometer that works the pulse width modulator on the 555?) slick
. . .

Build your own pump? I cobbled together a pump from a loud speaker
and some strips of latex to use as check valves (ala aquarium pumps).
Mine was to provide puffs of air across a spark gap to quench the
spark - worked with 60 cycles to quench a 60 cycle spark. I only used
one check valve since the fluid in the tube (air in my case) had
inertia and once it was moving down the tubing it didn't want to come
back during the refill stroke of the voice coil. (and the length of
tubing was resonant at 60 hertz with air in it) - not for liquid but
it wouldn't be a big deal to use a *** of thin latex (like a dental
dam from a drug store) to isolate the speaker cone from the fluid.
(latex is fine with water but doesn't like hydrocarbon oils).

It would be a piece of cake to modify an aquarium pump with a solenoid
driver instead of the magnet/AC coil they use. The parts are liquid
proof (plastic enclosure) Buena N diaphragm (from the looks of it) and
silicone rubber check valves. Vary the delivery by varying the stroke
with an adjustable stop on the solenoid driver so it limits the range
of motion.

Then you have Archimedes pumps, bucket pumps, etc if lifting water
without the need for pressure is the game.

Boggles the mind: don't it? I could have a lot of fun with this.



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Wow! Thank you so much for providing me with all of these ideas. Ive
looked into the "positive displacement pump" solution and found just
the companies who might be able to help me out.. I just hope the cost
isn't absurd.

This page may contain the pump I'm looking for:
http://www.micropump.com/products/pumps/gear/

Do you think the Series GB pump would work? It seems like if I get
could the correct mL/rev and the right rev speed, I could get a perfect
drip!

Again, thank you so much!

-Sam

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