Detecting Water Droplet Electronically

[Newsgroups]

Could any point me in the right direction for detecting a falling water
droplet electronically? This is being done for a photograph so the water
droplet must free fall without hitting anything. Can't be distorted in any
way. The droplet is not accelerated other then what gravity provides. Only
needs to fall about 1 or 2 feet. This turned into a larger problem then I
first expected. I've tried the following:

1) Laser pointer into a Cadmium Sulfide photocell but the light pretty much
travels straight through the clear water and the photocell doesn't react
fast enough.

2) Infrared beam has the same problem.

3) Built a small two plated capacitor (with air as the dielectric) using
copper clad boards. Measured 27 pf and it would change very nicely when I
held a water droplet between the plates. But when the droplet is traveling
through the air, again it was to fast to get a reaction larger enough to
measure.

I'm going to dismiss hall-effect thinking that water droplets have a slight
electronical charge not a magnetic one right? Maybe I just need to redesign
the detection circuits for the above (capacitor or photocell) to make them a
ton more sensitive. In any case I would love the input of people much
smarter than me

Any help or pointers towards web pages, discussion groups, physics forums
etc would help. I'm not a student here doing home work. Just a guy in my
back room having fun with electronics and his new D70 camera.

thanks
Dan

 

[JB]

Could any point me in the right direction for detecting a falling water
droplet electronically? This is being done for a photograph so the water
droplet must free fall without hitting anything. Can't be distorted in any
way. The droplet is not accelerated other then what gravity provides. Only
needs to fall about 1 or 2 feet. This turned into a larger problem then I
first expected. I've tried the following:

1) Laser pointer into a Cadmium Sulfide photocell but the light pretty much
travels straight through the clear water and the photocell doesn't react
fast enough.

2) Infrared beam has the same problem.

3) Built a small two plated capacitor (with air as the dielectric) using
copper clad boards. Measured 27 pf and it would change very nicely when I
held a water droplet between the plates. But when the droplet is traveling
through the air, again it was to fast to get a reaction larger enough to
measure.

I'm going to dismiss hall-effect thinking that water droplets have a slight
electronical charge not a magnetic one right? Maybe I just need to redesign
the detection circuits for the above (capacitor or photocell) to make them a
ton more sensitive. In any case I would love the input of people much
smarter than me

Any help or pointers towards web pages, discussion groups, physics forums
etc would help. I'm not a student here doing home work. Just a guy in my
back room having fun with electronics and his new D70 camera.

You could try using hot water and detecting the droplets using a PIR
sensor/switch (bog-standard intruder/motion sensor type device for security
lighting etc..) These often have variable sensitivity and detection
distance/angle.You will need to disable or cover the auxilliary photocell
(for switching the unit off during the daytime). You could then use it in
normal visible light.

JB

 

[Fred Bloggs]

Could any point me in the right direction for detecting a falling water
droplet electronically? This is being done for a photograph so the water
droplet must free fall without hitting anything. Can't be distorted in any
way. The droplet is not accelerated other then what gravity provides. Only
needs to fall about 1 or 2 feet. This turned into a larger problem then I
first expected. I've tried the following:

1) Laser pointer into a Cadmium Sulfide photocell but the light pretty much
travels straight through the clear water and the photocell doesn't react
fast enough.

2) Infrared beam has the same problem.

3) Built a small two plated capacitor (with air as the dielectric) using
copper clad boards. Measured 27 pf and it would change very nicely when I
held a water droplet between the plates. But when the droplet is traveling
through the air, again it was to fast to get a reaction larger enough to
measure.

I'm going to dismiss hall-effect thinking that water droplets have a slight
electronical charge not a magnetic one right? Maybe I just need to redesign
the detection circuits for the above (capacitor or photocell) to make them a
ton more sensitive. In any case I would love the input of people much
smarter than me

Any help or pointers towards web pages, discussion groups, physics forums
etc would help. I'm not a student here doing home work. Just a guy in my
back room having fun with electronics and his new D70 camera.

thanks
Dan

Arrange for a steady stream of droplets into water and phase lock an
oscillator to microphone input of the "plop"- then when you want to snap
a pic or whatever, press a button asynchronously and fire the trigger at
a manually adjustable delay into each PLL cycle until you get it right.

 

[Rene Tschaggelar]

Could any point me in the right direction for detecting a falling water
droplet electronically? This is being done for a photograph so the water
droplet must free fall without hitting anything. Can't be distorted in any
way. The droplet is not accelerated other then what gravity provides. Only
needs to fall about 1 or 2 feet. This turned into a larger problem then I
first expected. I've tried the following:

1) Laser pointer into a Cadmium Sulfide photocell but the light pretty much
travels straight through the clear water and the photocell doesn't react
fast enough.

A photocell is never fast enough. Use a photodiode.

Rene

 

[Ben Bradley]

Could any point me in the right direction for detecting a falling water
droplet electronically? This is being done for a photograph so the water
droplet must free fall without hitting anything. Can't be distorted in any
way. The droplet is not accelerated other then what gravity provides. Only
needs to fall about 1 or 2 feet. This turned into a larger problem then I
first expected. I've tried the following:

1) Laser pointer into a Cadmium Sulfide photocell but the light pretty much
travels straight through the clear water and the photocell doesn't react
fast enough.

The problem here is more the slow reaction time of the photocell
than anything else. Use a photodiode. The droplet will refract the
light enough to cause a significant dip in the light seen by the
diode. You may want to add a slight delay in triggering the camera
with this, unless you want a pic with the laser shining on it.

2) Infrared beam has the same problem.

3) Built a small two plated capacitor (with air as the dielectric) using
copper clad boards. Measured 27 pf and it would change very nicely when I
held a water droplet between the plates. But when the droplet is traveling
through the air, again it was to fast to get a reaction larger enough to
measure.

Capacitance would change instantaneously as the droplet falls
through, so you just need a faster measurement technique. Use the
capacitance as one of the frequecy-determining elements in an
oscillator of about 1MHz, and have a circuit (perhaps a PLL) watch the
frequency change as the droplet falls through.

 

[logized]

Could any point me in the right direction for detecting a falling water
droplet electronically? This is being done for a photograph so the water
droplet must free fall without hitting anything. Can't be distorted in any
way. The droplet is not accelerated other then what gravity provides. Only
needs to fall about 1 or 2 feet. This turned into a larger problem then I
first expected. I've tried the following:

1) Laser pointer into a Cadmium Sulfide photocell but the light pretty much
travels straight through the clear water and the photocell doesn't react
fast enough.

2) Infrared beam has the same problem.

3) Built a small two plated capacitor (with air as the dielectric) using
copper clad boards. Measured 27 pf and it would change very nicely when I
held a water droplet between the plates. But when the droplet is traveling
through the air, again it was to fast to get a reaction larger enough to
measure.

I'm going to dismiss hall-effect thinking that water droplets have a slight
electronical charge not a magnetic one right? Maybe I just need to redesign
the detection circuits for the above (capacitor or photocell) to make them a
ton more sensitive. In any case I would love the input of people much
smarter than me

Any help or pointers towards web pages, discussion groups, physics forums
etc would help. I'm not a student here doing home work. Just a guy in my
back room having fun with electronics and his new D70 camera.

thanks
Dan

Dan,
Maybe you could use a motion detection camera to sense the water
droplet appearing, see http://www.supervisioncam.com/
It can make a sound or run a program to trigger your camera. Don't know if
it would be fast enough though.

Dave

 

[Paul Hovnanian P.E.]

A photocell is never fast enough. Use a photodiode.

Yep. And try mounting the photodiode off axis from the source beam and
detecting the scatter or reflection from the drop.

 

[Mike Page]

Capacitance would change instantaneously as the droplet falls
through, so you just need a faster measurement technique. Use the
capacitance as one of the frequecy-determining elements in an
oscillator of about 1MHz, and have a circuit (perhaps a PLL) watch the
frequency change as the droplet falls through.

Though I favour an optical technique this one has me thinking. Other
devices work on capacitance change, including condensor microphones
(which are well written up). The idea is you maintain a constant charge,
so the change in capacitance manifests as a voltage (Q=CV). Involves a
high impedance buffer, which should be do-able with a CMOS opamp and
some careful cabling.

Regards,
Mike.

 

[John Fields]

Could any point me in the right direction for detecting a falling water
droplet electronically?

....

---
get yourself an optical slotted switch with a wide gap, like this:

http://www.optekinc.com/pdf/OPB800L.pdf

Digi-Key either has some or some like it.

Pull up the phototransistor's collector with whatever value is
recommended in the data sheet, then force enough current through the
LED to get a stable low out of the transistor's collector with nothing
in the gap, then when a drop of water falls through the optical axis
of the switch, the transistor's output will go high. If you get the
drop exactly centered you may get two high peaks with a valley in
between; the first peak when the droplet first breaks the beam and
reflects and diffracts the IR away from the sensor, then the valley
when the droplet is normal to the beam and lets some IR through, and
then the final peak as the droplet is leaving the beam.

 

[Genome]

| Could any point me in the right direction for detecting a falling
water
| droplet electronically? This is being done for a photograph so the
water
| droplet must free fall without hitting anything. Can't be distorted
in any
| way. The droplet is not accelerated other then what gravity provides.
Only
| needs to fall about 1 or 2 feet. This turned into a larger problem
then I
| first expected. I've tried the following:
|
| 1) Laser pointer into a Cadmium Sulfide photocell but the light pretty
much
| travels straight through the clear water and the photocell doesn't
react
| fast enough.
|
| 2) Infrared beam has the same problem.
|
| 3) Built a small two plated capacitor (with air as the dielectric)
using
| copper clad boards. Measured 27 pf and it would change very nicely
when I
| held a water droplet between the plates. But when the droplet is
traveling
| through the air, again it was to fast to get a reaction larger enough
to
| measure.
|
| I'm going to dismiss hall-effect thinking that water droplets have a
slight
| electronical charge not a magnetic one right? Maybe I just need to
redesign
| the detection circuits for the above (capacitor or photocell) to make
them a
| ton more sensitive. In any case I would love the input of people much
| smarter than me
|
| Any help or pointers towards web pages, discussion groups, physics
forums
| etc would help. I'm not a student here doing home work. Just a guy in
my
| back room having fun with electronics and his new D70 camera.
|
| thanks
| Dan
|
|
|
|

Mount the camera below the point where the drop is detected so it's
passing by when the camera is triggered?

DNA

 

[Jamie]

dropping water passing the plates (not touching) should product an
electrical charge. this is the bases of the home made thunder shower.
i don't remember the exact construction but it can be found on the
net in any case, one could use a FET input with diode suppression from
the plates to detect this charge.
another approach is to use U-sonic, since it can be narrowed down to a
small stream and water will some what absorb it, i think i could make
for a good absent detector when the water is passing through its path.

 

[mike]

Could any point me in the right direction for detecting a falling water
droplet electronically? This is being done for a photograph so the water
droplet must free fall without hitting anything. Can't be distorted in any
way. The droplet is not accelerated other then what gravity provides. Only
needs to fall about 1 or 2 feet. This turned into a larger problem then I
first expected. I've tried the following:

1) Laser pointer into a Cadmium Sulfide photocell but the light pretty much
travels straight through the clear water and the photocell doesn't react
fast enough.

2) Infrared beam has the same problem.

3) Built a small two plated capacitor (with air as the dielectric) using
copper clad boards. Measured 27 pf and it would change very nicely when I
held a water droplet between the plates. But when the droplet is traveling
through the air, again it was to fast to get a reaction larger enough to
measure.

I'm going to dismiss hall-effect thinking that water droplets have a slight
electronical charge not a magnetic one right? Maybe I just need to redesign
the detection circuits for the above (capacitor or photocell) to make them a
ton more sensitive. In any case I would love the input of people much
smarter than me

Any help or pointers towards web pages, discussion groups, physics forums
etc would help. I'm not a student here doing home work. Just a guy in my
back room having fun with electronics and his new D70 camera.

thanks
Dan

Mike's rule #2...Never measure anything when you can control it instead.
Use an electromagnet to "shake loose a droplet". A little physics will
tell you when the drop will be where you want it. Delay the camera
trigger by that amount.
mike

--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Compaq Aero floppy,ram,battery.
FT-212RH 2-meter 45W transceiver.
Toshiba & Compaq LiIon Batteries, Test Equipment
30pS pulser, Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Rolavine]

Subject: Re: Detecting Water Droplet Electronically

From: mike [email protected]
Date: 7/12/2004 2:40 PM Pacific Daylight Time
Message-id: <[email protected]>


Mike's rule #2...Never measure anything when you can control it instead.
Use an electromagnet to "shake loose a droplet". A little physics will
tell you when the drop will be where you want it. Delay the camera
trigger by that amount.
mike

Yeah, or create the drop by opening and closing a solenoid? I went with the'
control i't idea too, but the sensing ideas were all really pretty amazing.
There are some real good engineers on this group!

Rocky

 

[mike]

Yeah, or create the drop by opening and closing a solenoid? I went with the'
control i't idea too, but the sensing ideas were all really pretty amazing.
There are some real good engineers on this group!

Rocky

There's an even simpler method. Make a stream of drops close together.
Snap a few random pictures. Eventually, you'll get one positioned where
you want it. Ain't statistics grand?
mike

--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Compaq Aero floppy,ram,battery.
FT-212RH 2-meter 45W transceiver.
Toshiba & Compaq LiIon Batteries, Test Equipment
30pS pulser, Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Dan]

Wow, thanks for feedback. The photodiode seems to win the vote and John's
idea of using the optical slotted switch (which I have plenty of from old
computer mice) is perfect. Maybe after my fun is over I'll play with the
capacitor approach. I liked Ben's idea of using the 1 MHz osc, that would be
fun to try. Sound would be an option too as Fred pointed out but I really
want to try to get a fix on the current droplet-in-flight rather than one
following
for reasons I hadn't fully explained. Yes the plot thickens ..

The rest of the story is I've already built a "Common Pin" launcher. Reminds
me of a little rail gun if you could see it (I could always put a picture up
at my site). Anyway its activated via a solenoid (you knew that was coming).
My Nikon 995 has a serial port for control of all its functions and I have
the protocol and commands from the net. I'm currently finishing up the
little reservoir with the tiny tube to drop the water droplets. And the
air intake is controlled by a floppy stepper motor to control the drops, the
last
piece was the water detection for feedback and mostly timing.

The (hopeful) final results will be a macro picture of a common pin
projectile hitting a water droplet in mid air. It's probably been done a
million times but I've never done it and wanted the exercise of learning
what it would take. Would be fun to have the pictures also

- Dan

P.S. You guys are great, thanks for the all the great ideas.

 

[John Fields]

Could any point me in the right direction for detecting a falling water
droplet electronically?

....

---
get yourself an optical slotted switch with a wide gap, like this:

http://www.optekinc.com/pdf/OPB800L.pdf

Digi-Key either has some or some like it.

Pull up the phototransistor's collector with whatever value is
recommended in the data sheet, then force enough current through the
LED to get a stable low out of the transistor's collector with nothing
in the gap, then when a drop of water falls through the optical axis
of the switch, the transistor's output will go high. If you get the
drop exactly centered you may get two high peaks with a valley in
between; the first peak when the droplet first breaks the beam and
reflects and diffracts the IR away from the sensor, then the valley
when the droplet is normal to the beam and lets some IR through, and
then the final peak as the droplet is leaving the beam.