Hello Bruce, when I first read your question it sounded like you were
trying to make an IV drip. There has been quite a bit of work done on
your exact problem. The idea I had was to use a stepper motor to
control the drip and then to control the stepper/valve with a PC. I
searched using "stepper motor IV drip" and found some interesting
In this paper we present the development and implementation of an
intravenous infusion controller system based on fpga´s. The system
receives information of an infusion drop sensor and controls the drop
flow by giving the direction and number of steps of a stepper motor,
which compress the drip-feed hose. The system consists of a mixed
implementation of software and hardware. The software was implemented
in C++ and the hardware was implemented by using FPGA´s.
This is a pretty detailed description of a system that will do
exactly what you require. I understand that you wanted something
simple, but what you want is not that easily done.
IV Bag Drip Rate Flow Control Valve
We designed a flow control valve using a stepper motor control and
weigh scales. This project proved that a reliable valve could be
developed to control and monitor the drip rate of an IV bag. We also
developed a custom Windows user interface to enable researchers to
easily adjust drip rates and capture data.
This is another company that has designed a drip control using a
stepper motor. Instead of counting drops, they use weight change to
calculate flow rate.
If you don't want to stick with the gravity flow concept, here is another approach:
The positive displacement metering pump is generally the first choice
for providing precise and repeatable flow in many medical device fluid
dispensing applications. Understanding the full range of established
and newer metering pump technologies available allows for the
selection of the best metering pump to meet the fluid handling needs
of the application.
Here is a patent application for your device:
Electrically controlled intravenous infusion set , United States Patent 4038982
An electronically controlled intravenous infusion set of the gravity
feed type having a flow path including a drip chamber and an internal
valve for regulating flow through the set. Electromagnetic valve
operating structure, positioned outside the IV set, controls the
internal valve in response to an electronic control system. The
electronic control system serves to open the valve to allow a drop to
fall, and includes a control circuit. The control circuit includes an
optical drop detector, associated with but positioned outside the drip
chamber, which senses the falling drop and signals the control circuit
to close the valve. The control circuit also includes a variable
frequency clock and associated digital selectors for affording an
attendant the ability to precisely select a desired drip rate. An
alarm system, operating on digital principles, senses high drop rate
or low drop rate conditions and, in response thereto, puts the control
system into an alarm condition. The alarm system includes means for
digitally adjusting the sensitivity thereof to provide high
sensitivity at low drip rates but to decrease the sensitivity at
higher rates so that premature alarm conditions are avoided.
I hope this will give you some good ideas. If I have misunderstood
what you are looking for, please ask for a clarification and I will
try and help.
Good luck with your design, Redhoss