3vdc motor PWM problem

[James Thompson]

---
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.

No, not the drop sensor but the synchronizing of the strobe.
The other was just my 2 cents.
I saw someone else mention a solenoid pump to precisely pump one drop with
each pulse. That may well be the whole solution and get rid of the old dc
motor pump. It would give precise control of both drop frequency and strobe.
JTT

 

[randomname]

No, not the drop sensor but the synchronizing of the strobe.
The other was just my 2 cents.
I saw someone else mention a solenoid pump to precisely pump one drop with
each pulse. That may well be the whole solution and get rid of the old dc
motor pump. It would give precise control of both drop frequency and strobe.
JTT

Where could I find a suitable solenoid? I've never used one before.
I'd love to have that type of precision with the drops.

 

[jasen]

Where could I find a suitable solenoid? I've never used one before.
I'd love to have that type of precision with the drops.

try an auto wrecker, some vehicles have solenoid based fuel pumps, all you'd
need to do is open it up and short out (or bypass) the contacts (so it doesn't
run at its own rate) and feed it 12V pulses. (actually if the rate you want
is low enough or the pulses narrow enough you may not need to modify it at
all.

Bye.
Jasen

 

[James Thompson]

Where could I find a suitable solenoid? I've never used one before.
I'd love to have that type of precision with the drops.

Use 2 one-way valves like the airline valve for fish pumps, and between them
a small soft rubber bulb. Around that fashion the actuator of a solenoid
that will squeeze the bulb and pump the water. hmm maybe even adapt a
small aquarium air pump to do water. I have one here I will try out and get
back to you.

 

[James Thompson]

Use 2 one-way valves like the airline valve for fish pumps, and between
them a small soft rubber bulb. Around that fashion the actuator of a
solenoid that will squeeze the bulb and pump the water. hmm maybe even
adapt a small aquarium air pump to do water. I have one here I will try
out and get back to you.

OK. It works very well. I removed the chamber from an aquarium air pump
and with it submerged, by tapping the rubber cap - it pumps fluid just fine.
All it needs now is a small magnet attached to the rubber cup and a coil
over it. By pulsing the coil, you will get drops of water.
The pump I used is brand Aquaculture single outlet JTT

 

[Rich Grise]

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

Have you tried an accumulator and needle valve? Or maybe something like
a fuel injector thingie? For making drips, that is - the talk of the
astables is for the duty cycle of the motor, right?

Cheers!
Rich

 

[Rich Grise]

try an auto wrecker, some vehicles have solenoid based fuel pumps, all you'd
need to do is open it up and short out (or bypass) the contacts (so it doesn't
run at its own rate) and feed it 12V pulses. (actually if the rate you want
is low enough or the pulses narrow enough you may not need to modify it at
all.

What about an EFI injector? Or would running water through one wreck it?

Thanks,
Rich

 

[John Fields]

What about an EFI injector? Or would running water through one wreck it?

 

[John Fields]

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...

 

[jasen]

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.

60Hz? that's a high rate for 6mm drops

they'd have to be doing 0.36 m/s to avoid the next drop behind them

at 10m/s^2 it'd take them 36 ms to achive that speed

I guess you could use a stream of water and just let it break into drops as
it falls, or maybe modulate it somehow.

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...

you'll probably get 120Hz modulation for free with that setup


Hmmm.


flow modulator:

__
L.V. AC supply ===== [ ]
/ \ ---- sub-woofer
/ \
_/ \_ valve
| | T
tank | .|------+------- water input
|~~~~~~~~|
| |
`---||---'
`------ hole

Bye.
Jasen

 

[randomname]

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

Welcome aboard

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.

If you get this part working, could you let me know how it's done? I'd
love to try drop detection in the future... but with it you really need
a PIC to get the slow motions forwards/backwards. That's why I'm
gunning for constant drip

My goal will be to generate 1/4" diameter drops that fall through
12" with a new drop being generated every 16ms or so.

1/4" drops sound a little big... you should probably use a McDonalds
straw for that (which I'm going to try tomorrow). I'm using 3/16" OD
aquarium tube, and my drops are 3/8", which are a very nice size.

As per the 16ms... that will prove to be very difficult. The fastest
drip I can get before it turns into a stream (in which case the drops
are extremely erratic and tiny, but much more frequent) is such that
there are 3 drops in the air at any given moment. Considering the fall
is 3.5 inches.. that means there's a drop roughly every 45ms. It
should be tough to cut that in third.. and if you manage somehow do let
me know!

Another issue you'll run into is that 12" is pretty high. Mine was
originally this height. I figured: hey, I want to watch the drop for a
long time and see a nice splash at the end, too.

The problem here is that even at the 45ms rate, where the drops hit is
a very chaotic area. You'll get bubbles crowding up, and splash
everywhere, and since these arent periodic it will ruin the effect.
I've found the best height to be a little under 4". The impact region
really is the most impressive part of this piece, IMO. It gets ruined
when the drops come from too high, too fast. (Since the drop rebound
hits the next drop falling)

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.

If you're rate of dripping is 16ms, and the height is 12", then you
will have 16 drops in the air at any given time.

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.

I wish I had a valve. My valve is a c-clamp tightening the rubber
tube.

Anyway, best of luck. Can't wait to see how you do!

-sam

 

[James Thompson]

Welcome aboard


If you get this part working, could you let me know how it's done? I'd
love to try drop detection in the future... but with it you really need
a PIC to get the slow motions forwards/backwards. That's why I'm
gunning for constant drip


1/4" drops sound a little big... you should probably use a McDonalds
straw for that (which I'm going to try tomorrow). I'm using 3/16" OD
aquarium tube, and my drops are 3/8", which are a very nice size.

As per the 16ms... that will prove to be very difficult. The fastest
drip I can get before it turns into a stream (in which case the drops
are extremely erratic and tiny, but much more frequent) is such that
there are 3 drops in the air at any given moment. Considering the fall
is 3.5 inches.. that means there's a drop roughly every 45ms. It
should be tough to cut that in third.. and if you manage somehow do let
me know!

Another issue you'll run into is that 12" is pretty high. Mine was
originally this height. I figured: hey, I want to watch the drop for a
long time and see a nice splash at the end, too.

The problem here is that even at the 45ms rate, where the drops hit is
a very chaotic area. You'll get bubbles crowding up, and splash
everywhere, and since these arent periodic it will ruin the effect.
I've found the best height to be a little under 4". The impact region
really is the most impressive part of this piece, IMO. It gets ruined
when the drops come from too high, too fast. (Since the drop rebound
hits the next drop falling)


If you're rate of dripping is 16ms, and the height is 12", then you
will have 16 drops in the air at any given time.


I wish I had a valve. My valve is a c-clamp tightening the rubber
tube.

Anyway, best of luck. Can't wait to see how you do!

-sam

Sam, if you want me to take a picture of the pump from the aquarium air pump
I will. By controlling the amplitude of the pulse on the coil that pushes
the pump chamber - you control the amount of fluid it pumps per pulse. This
pump is small, not the size of the whole air pump as it don't use the 120
volt coil.
You said in another post that you would prefer not to make the pump yourself
but is that not the fun of it?
I am also going to build a few of these for Christmas presents as it would
truly make unique gifts. Thanks for the inspiration

 

[John Fields]

Welcome aboard


If you get this part working, could you let me know how it's done? I'd
love to try drop detection in the future... but with it you really need
a PIC to get the slow motions forwards/backwards. That's why I'm
gunning for constant drip

---
I'm planning on using an IR opto switch, with the drop breaking the
beam as it falls. Basically an IRLED as the emitter and a
phototransistor as the detector. The IRLED will keep the
phototransistor in saturation until the drop interrupts the beam, at
which time the detector will come out of saturation, its output will
go high, and that high-going edge will be used to start the strobe
delay.

If you substitute an LDR for the delay timing resitor then you can
change its resistance by shining an LED (or an incandescent lamp) on
it. That way, you can use, say, a slow ramp generator to illuminate
the lamp and change the delay, so the column of drops will rise and
fall slowly, automatically.
---

1/4" drops sound a little big... you should probably use a McDonalds
straw for that (which I'm going to try tomorrow). I'm using 3/16" OD
aquarium tube, and my drops are 3/8", which are a very nice size.

---
3/8" drops?
---

As per the 16ms... that will prove to be very difficult. The fastest
drip I can get before it turns into a stream (in which case the drops
are extremely erratic and tiny, but much more frequent) is such that
there are 3 drops in the air at any given moment. Considering the fall
is 3.5 inches.. that means there's a drop roughly every 45ms. It
should be tough to cut that in third.. and if you manage somehow do let
me know!

---
Change of plans... I want to have the 12" fall, and I want only one
drop to be visible when it's halfway down, so I'll need to generate
drops every 6", which is 176ms apart. That's about 5.7Hz, so
there'll be a lot of flicker, but that's where I want to start.
---

Another issue you'll run into is that 12" is pretty high. Mine was
originally this height. I figured: hey, I want to watch the drop for a
long time and see a nice splash at the end, too.

The problem here is that even at the 45ms rate, where the drops hit is
a very chaotic area. You'll get bubbles crowding up, and splash
everywhere, and since these arent periodic it will ruin the effect.
I've found the best height to be a little under 4". The impact region
really is the most impressive part of this piece, IMO. It gets ruined
when the drops come from too high, too fast. (Since the drop rebound
hits the next drop falling)

---
I'm more interested in manipulating the drop(s) in the column than I
am in the impact, right now, so I plan to diffuse the drops when
they return to the tank so they won't create pressure pulses which
could affect the pump. Maybe that's part of the problen you were
having originally with your pump's stability?
---

If you're rate of dripping is 16ms, and the height is 12", then you
will have 16 drops in the air at any given time.

 

[randomname]

Sam, if you want me to take a picture of the pump from the aquarium air pump
I will. By controlling the amplitude of the pulse on the coil that pushes
the pump chamber - you control the amount of fluid it pumps per pulse. This
pump is small, not the size of the whole air pump as it don't use the 120
volt coil.
You said in another post that you would prefer not to make the pump yourself
but is that not the fun of it?
I am also going to build a few of these for Christmas presents as it would
truly make unique gifts. Thanks for the inspiration

Yea a picture would be great. Have you tested it out? I'd like how
well it performs.

My best results are 22 drops/second, 6mm drop diameter.

-sam

 

[randomname]

I'm planning on using an IR opto switch, with the drop breaking the
beam as it falls. Basically an IRLED as the emitter and a
phototransistor as the detector. The IRLED will keep the
phototransistor in saturation until the drop interrupts the beam, at
which time the detector will come out of saturation, its output will
go high, and that high-going edge will be used to start the strobe
delay.

If you substitute an LDR for the delay timing resitor then you can
change its resistance by shining an LED (or an incandescent lamp) on
it. That way, you can use, say, a slow ramp generator to illuminate
the lamp and change the delay, so the column of drops will rise and
fall slowly, automatically.

This is over my head... I know an LDR changes resistance as a function
of light received. But how will you ramp it? Seems like it could be
done, but you'll need another timer to somehow set when the ramp gets
reset, no?

3/8" drops?

Yea I misread my ruler... it was late at night. Turns out my drops are
about the size of your hypothetical drops. I actually calculated the
size using the given drops/second, mL/second, density of water, and 4/3
pi r^3... turns out they are about 6mm.

Change of plans... I want to have the 12" fall, and I want only one
drop to be visible when it's halfway down, so I'll need to generate
drops every 6", which is 176ms apart. That's about 5.7Hz, so
there'll be a lot of flicker, but that's where I want to start.

I just set mine up to that speed. It look's pretty cool... it appears
to be much more stable at this drip rate.

I'm more interested in manipulating the drop(s) in the column than I
am in the impact, right now, so I plan to diffuse the drops when
they return to the tank so they won't create pressure pulses which
could affect the pump. Maybe that's part of the problen you were
having originally with your pump's stability?

The impact is really beautiful. The good news is that at 5Hz you
should be ok, I think the rebound drop will be on its way down when the
next drop comes to hit it. Should look pretty cool, actually.

More than enough! At 22Hz, you need .08L/min... so you get the idea of
the small quantity of water that needs to be delivered. Let me know
how it goes!

-sam

 

[Rich Grise]

The problem here is that even at the 45ms rate, where the drops hit is
a very chaotic area. You'll get bubbles crowding up, and splash
everywhere, and since these arent periodic it will ruin the effect.
I've found the best height to be a little under 4". The impact region
really is the most impressive part of this piece, IMO. It gets ruined
when the drops come from too high, too fast. (Since the drop rebound
hits the next drop falling)

You could try a piece of scotch-brite at the landing zone - the drops
wouldn't splash much, I'd think.

And slant it, so the water runs off into your reservoir.

Good Luck!
Rich