I am looking for a simple device that dispenses liquids that is
computer controlled via a USB or serial port. Nothing fancy but I just
need to control the amount of a liquid that get dispensed in a bottle.
For example when you go to Home Depot and get a certain color paint,
they put the can of white paint underneath a nozzle, enter in the
color on the computer and the computer dispenses a few different
colors to create that paint. I am looking for that kind of dispenser.
I would write the software. Any ideas? Sorry is this is the wrong
group to post this in but I am trying to figure out where to start.
A small flowmeter and a computer controlled valve come to mind, but that
intuitively doesn't seem very precise for an application like mixing paint.
If you can be guaranteed that the liquid you're using always has a constant
pressure or flow rate you can time how long a valve is opened for.
I don't like the timing based approach, for these very reasons. I'd prefer
to measure in terms of quantity if I did this project myself - the loss of
weight in the source tank as the liquid is pumped out for example, or
perhaps an ultrasonic or optical method of measuring the level of the liquid
surface (that would limit the speed you could pump at, of course, to avoid
waves or splashing throwing off the reading...
I think most liquid dispensers are based on positive displacement pumps,
essentially running in reverse. The (relative) incompressibility of a
liquid works well this way. Essentially, fill a cup (piston, cavity,
volume, what have you) turn it out, count one micro unit of
All the manual paint mixers I've ever seen in the last 40 years or so
work this way. Don't know about the automatic ones, but I assume they're
similar. The paint is first measured into a cylinder that will accept
only X amount, depending on the depth setting. The paint is then pressed
out of the cylinder. IOW, the paint is not measured in "real time."
Author: Constructing Robot Bases,
Robot Builder's Sourcebook, Robot Builder's Bonanza
This is my first Usenet posting using google groups, so hope this goes
I thought of something along these lines recently while coming up with
ideas for a cheap dosing pump for my marine aquariums. It would need
something that is not prone to clogging as the calcium solution used
causes deposits to build up quickly.
Most existing solutions use peristaltic pumps. They can be pretty
expensive and hard to find though. My idea was to use a calibrated
length of tubing to output a fixed volume. Hope I can explain this
without having to resort to ASCII art :-)
Fluid to be dispensed is in a *sealed* bottle with three openings in
One opening admits a tube that ends in the fluid, the second is a
tube that ends in the air above the fluid and the third opening is a
line to an air pump.
The fluid tube goes into a 2 way valve (or 2 valves in a manifold)
that switches its output between fluid and air. The output of this
valve leads to the calibrated length of tube. Let's say we want to
measure out 100mL of fluid: we put an optical sensor on the tube
(tubing is transparent at that wavelength) at a distance from the
valve output corresponding to 100mL.
To dispense 100mL we switch the valve to the "Air" position and turn
on the air pump. Air flows into the bottle and out of the air tube,
through the valve and past the sensor. This ensures that the line is
Now we switch the valve to the "Fluid" position and monitor the opto
sensor for an air->fluid transition. WHen we see the transition, it
means we have 100 uL of fluid in the tube, now we switch the valve
back to the "Air" position and look for a fluid->air transition at the
We have now dispensed a fairly accurate 100mL of fluid!!! Repeat as
necessary until you get to the desired volume.
Haven't built this yet as the only valve manifold I have is a bit
leaky, but I plan on trying it. Aquarium air pumps are cheap and a
single pump can run many of these contraptions, tubing is almost free
and solenoid valves can be found on the surplus market. It should be
possible to build a gravity-fed version that does not require an air
hope that helps
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.