Searching \ for '[EE] sensor ideas...' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: techref.massmind.org/techref/io/sensors.htm?key=sensor
Search entire site for: 'sensor ideas...'.

Exact match. Not showing close matches.
PICList Thread
'[EE] sensor ideas...'
2006\07\22@195009 by CSB

flavicon
Hello,
 I'm trying very hard to find a good solution for this but
haven't managed yet...

The project is a chronograph, to measure muzzle exit velocity.
Object can be metal (pellet) or plastic, so I can't rely
on a magnetic field. A capacitance sensor would be a bit
complex, since the nature of the object is not pre-
determined and exterior influence must be taken into account
(self-calibration, etc. etc.) So I see one possibility: an
optical sensor. Well, at least one, and the second sensor
could be a mecanical one (intercepts projectile)

My device needs to tolerate a lot of imprecision from the
operator. I.E. I can't expect the projectile to go exactly
accross a laser beam...

I thought of an IR led w/ phototransitor on the other side.
But I don't know if a small object could cause a noticeable
change at the photodetector, since most of the light is
still going to reach it around the projectile.

Would modulating the IR help discern a small variation ?

Or, a comparator circuit whose trigger level is very close
to the 'ambient' light level ?

Has anyone experimented with such sensors/applications?

Any ideas will be greatly appreciated...
Christian  VA2CBW

2006\07\22@200721 by Jinx

face picon face
> Has anyone experimented with such sensors/applications?

Ages ago, briefly. My neighbour was a hunter experimenting
with cartridge powder mixtures. He wanted to know how the
variations affected range and velocity

We came up with a couple of ideas that looked promising

One was a conducting strip of aluminium (cooking) foil under
a little tension that was shattered by both the bullet and the gas.
This breaking started the timer, a PIC running a 10us IRQ

At the receiving end, a light aluminium target (made of an old
printing plate), attached to a microswitch lever, was knocked
over to stop the timer

The only down side was that damage is sustained and it all had
to be reset, unlike optical, which I would have preferred

2006\07\22@200930 by Jinx

face picon face
> My device needs to tolerate a lot of imprecision from the operator

Why is that, Christian ?

2006\07\22@203025 by Denny Esterline

picon face
Chronographs are a fairly comon device nowadays.
A bit of googling turned up this one http://www.eabco.com/chronyshooting.htm
All the ones I've seen use upward pointed emmiter and a curved top reflector. The presence of the bullet blocks enough light to sense.

-Denny



{Quote hidden}

> --

2006\07\22@203856 by Bob Axtell

face picon face
CSB wrote:
{Quote hidden}

I think you can use a piezo microphone, like is used to detect breaking
glass.
It is extremely sensitive. It could be attacted to a mylar target
mechanically, and
when it is pierced by the bullet, the piezo would vibrate, sending a
pulse to the
PIC. You could use another one at the end of the test as well.

The only problem is that the mylar sheet will slow the bullet slightly
when it goes thru
the first sheet, making the measurement slightly inaccurate. If
possible, the initial
start sensor should be optical, I should think...

The start sensor COULD be an IR reflective device; as the bullet left,
the IR would
reflect off of its surface, and can then be detected.  To work it would
have to be located
close to the end of the muzzle, no more than 5mm distance. The sensor
would be subject
to gases, etc.

--Bob

2006\07\22@204159 by Matthew Miller

flavicon
face
How about using a microphone (with associated circuitry) to start the timer
and use Jinx's idea of a metal plate and microswitch to stop the timer?

Matthew

2006\07\22@204501 by CSB

flavicon
On Sun, 23 Jul 2006, Jinx wrote:

>> My device needs to tolerate a lot of imprecision from the operator
>
> Why is that, Christian ?
>

I'm thinking along the lines of 'productivity'... I.e. no need to set
the gun in a firm support, to line up exactly with a narrow beam. The
best would be : a large (~ 4cm, 1-2 inches) PVC pipe, through which
the operator just shoots, and as long as the projectile doesn't hit
the inside wall, the velocity reading will be valid (ignoring
Pythagoras for a moment).

The aluminum foil idea is a good one, but with very light objects
the speed diminution could be a problem. The desctructive nature of
the test is a bigger problem, though - changing the aluminum foil
eventually gets annoying and expensive (therefore counter-productive!)

A mechanical sensor is a reasonable solution for the second reading,
but the first sensor really has to be passive.

Maybe if I used a diffused IR led on one side, on the other side I
could sense a 'dip' in the photodetector when the object goes through
?

It really intrigues me how commercial chronographs work... I don't
suppose anyone has the schematic for one of them p-)

Christian  VA2CBW

2006\07\22@210440 by Jinx

face picon face
> I'm thinking along the lines of 'productivity'

To be honest, if it's something that's going to be used on a
regular basis, I'd rather buy one. They appear cheap enough

http://www.eabco.com/chronyshooting.htm

I'm sure wherever you are, they're available at a similar price

2006\07\22@210742 by CSB

flavicon
On Sat, 22 Jul 2006, Matthew Miller wrote:

> How about using a microphone (with associated circuitry) to start the timer
> and use Jinx's idea of a metal plate and microswitch to stop the timer?
>
> Matthew

Microphone= to 'listen' when the bullet goes past? Hmmm.... Could work. What
if I mounted a small microphone at the end of a small tube, perpendicular
to the projectile's path? Then amplify the signal and 'listen' for a variation.
If the mic is at 0.05 m from the source, it would take about 145 us for the
sound wave to propagate... It could be a problem with very high-speed shots,
though I don't expect them to be supersonic!


Well, it sounds (aha) a lot like the second sensor will be mechanical. It's
easy, and pretty unambiguous. One down, one to go...

Thanks for the ideas so far, I'm getting a better idea of what could work.
I still want more (ideas), though !


Christian VA2CBW

2006\07\22@211145 by CSB

flavicon


On Sat, 22 Jul 2006, Bob Axtell wrote:

> The only problem is that the mylar sheet will slow the bullet slightly
> when it goes thru
> the first sheet, making the measurement slightly inaccurate. If
> possible, the initial
> start sensor should be optical, I should think...

That's also what I think. Mylar sheet? I would not know where to find
any... and I would expect it to be most expensive!


> close to the end of the muzzle, no more than 5mm distance. The sensor
> would be subject
> to gases, etc.

Hadn't thought of that... Even if these are going to be mostly air guns,
some vaporized grease / debris is always a possibility...


Christian VA2CBW

2006\07\22@211627 by CSB

flavicon
> http://www.eabco.com/chronyshooting.htm

Hmm... not really expensive, but I'm sure it can be
made for less, and besides, where would the fun be !z

But how on earth does that one work ??? I see no
leds, no aluminum foil ! (no dwarves holding chronometers,
either :-)

Christian VA2CBW

2006\07\22@214029 by Jinx

face picon face
> But how on earth does that one work ???

IR it seems

http://www.shootingchrony.com/manual_CIR.htm

Presumably a curtain of IR is projected onto several receivers

http://www.eabco.com/images/chrony02.gif

"Setup is a snap. Just open the Chrony like a book, stick a nine-volt
battery inside, slide the metal rods that hold the sunscreens in place
and turn the one button on. Then, start shooting"

Some articles mention "sky-screens"

http://www.recguns.com/Sources/VIIC13b.html

"The chronos reviewed herein all utilize light-sensitive sensors that
detect then amplify a drop in the light level when the projectile passes
over it to trigger the start and stop gate circuits"

> (no dwarves holding chronometers, either :-)

They actually were in the picture but a contractual snafu had them
all airbrushed out

2006\07\22@214639 by Matthew Miller

flavicon
face
On Sat, Jul 22, 2006 at 09:12:11PM -0400, CSB wrote:
>
> Microphone= to 'listen' when the bullet goes past? Hmmm.... Could work. What
> if I mounted a small microphone at the end of a small tube, perpendicular
> to the projectile's path? Then amplify the signal and 'listen' for a variation.
> If the mic is at 0.05 m from the source, it would take about 145 us for the
> sound wave to propagate... It could be a problem with very high-speed shots,
> though I don't expect them to be supersonic!

I don't know how well a microphone will register the passage of a
projectile, but what I had in mind was to place the microphone next to the
muzzle. The report caused by the bullet and exhaust gases exiting the barrel
is what the microphone responds to. I want to think that this is the type of
setup that has been used by high-speed photography of bullets...

Matthew

2006\07\22@220414 by CSB

flavicon
On Sun, 23 Jul 2006, Jinx wrote:
>
> Some articles mention "sky-screens"
>
> http://www.recguns.com/Sources/VIIC13b.html
>

Ah ! thanks for the link, it answered quite few questions!
most importantly, it proves that optical sensors are a
practical solution...


Christian VA2CBW

2006\07\23@004644 by Dave King

flavicon
face
Microphones are overwhelmed by the muzzle blast. Or they are
with our avalanche guns. We found we could hear the breach work,
hear it recoil, even tell when the round hit, but the actual
point where it exited the muzzle was always referred to as "somewhere in
this bit" of the recording. We actually were
able to hear the impacts on a 3km shoot. Mind you we shoot 4lb
mortar like rounds so they tend to go smack nice.

Dave


{Quote hidden}

> -

2006\07\23@095640 by olin piclist

face picon face
CSB wrote:
> no need to set the gun in a firm support,

I'm no gun expert, but if the gun isn't firmly anchored, wouldn't the
resulting kickback make a noticeable decrease in the bullet speed?  After
all, momentum still has to ballance.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\07\23@095932 by olin piclist

face picon face
CSB wrote:
> Hmm... not really expensive, but I'm sure it can be
> made for less, and besides, where would the fun be !

This conflicts with your earlier statement where you said the main goal was
productivity.  Either you can buy something effective and ready to go off
the shelf and get on with things, or you can create your own that will
certainly cost more and probably won't be as good but will be a lot more
fun.

Make up your mind and pick one.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\07\23@114424 by CSB

flavicon

On Sun, 23 Jul 2006, Olin Lathrop wrote:

> This conflicts with your earlier statement where you said the main goal was
> productivity.  Either you can buy something effective and ready to go off
> the shelf and get on with things, or you can create your own that will
> certainly cost more and probably won't be as good but will be a lot more
> fun.
>

What's wrong with trying to optimize cost, efficiency and fun? Is there
anything preventing me from wanting an inexpensive home-made solution that
works the way I want it to? I thought that was the whole idea of 'doing it
yourself' ...




> I'm no gun expert, but if the gun isn't firmly anchored, wouldn't the
> resulting kickback make a noticeable decrease in the bullet speed?  After
> all, momentum still has to ballance.


Kickback => do you mean recoil ? (just so we talk about the same thing)
I don't think it will make a noticeable variation in speed. If, say, the
gun is moving backwards at 5 fps after the shot is fired, and the projectile
is moving out of the muzzle at 500 fps (or anywhere between 100 and a few
thousand), that means the bullet speed relative to the ground is 495 fps...
a 1% error. Of course I have no real data on that, but I'm sure the
difference won't be that big.

And it gives a better idea of what speeds can be attained in a normal
situation. If I'm timing an anchored gun, the speed obtained will be greater
than those that will be attained in a normal situation, i.e. with a human
holding the gun, dealing with real recoil.


Christian VA2CBW

2006\07\23@121929 by Mohit M. \(Lists\)

picon face
Olin Lathrop:
> I'm no gun expert, but if the gun isn't firmly anchored,
> wouldn't the
> resulting kickback make a noticeable decrease in the
> bullet speed?  After
> all, momentum still has to ballance.

Wouldn't that kickback/recoil happen right after the bullet
exits the muzzle? IMHO, it shouldn't make _any_ difference
to the bullet speed.

Mohit.

2006\07\23@160133 by Peter

picon face


On Sun, 23 Jul 2006, CSB wrote:

> What's wrong with trying to optimize cost, efficiency and fun? Is there
> anything preventing me from wanting an inexpensive home-made solution that
> works the way I want it to? I thought that was the whole idea of 'doing it
> yourself' ...

Quick, cheap, good, inexpensive, marketable, reliable, built using info
from a free mailing list - pick any zero.

Peter

2006\07\23@161836 by Wouter van Ooijen

face picon face
> Quick, cheap, good, inexpensive, marketable, reliable, built
> using info
> from a free mailing list - pick any zero.

In my experience for piclist answers to well-formulated questions (that
is important!)

Quick : within 8 -48h (reasonbly quick IMO)
cheap : my internet connection is not free, but not too expensive either
(but reading the messages takes quite some time - so maybe no that cheap
after all)
good : if you filter out the good answers :)
inexpensive : isn't that the same as cheap?
marketable : hey, that's my own responsibility!
reliable : as long as I do the filtering...
built using info from a free mailing list : just don't ask for the
perfect programmer design, prototype board design, language, compiler,
first PIC, religion, political persuasion, ...  

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\07\23@165032 by Richard Prosser

picon face
Maybe when the kit is operating, someone could do an experiment?
RP

On 24/07/06, Mohit M. (Lists) <spam_OUTmohit.listsTakeThisOuTspamgmail.com> wrote:
{Quote hidden}

> -

2006\07\23@190948 by Jinx

face picon face

> Wouldn't that kickback/recoil happen right after the bullet
> exits the muzzle? IMHO, it shouldn't make _any_ difference
> to the bullet speed.

According to

http://www.bsharp.org/physics/stuff/recoil.html

Secondary Recoil

There are actually two distinct recoils from a gun:

the first, primary recoil, which I've described above, conserves
momentum of the gun-bullet system.  However, a larger secondary
recoil comes slightly later, when the bullet leaves the muzzle: then
the hot expanding gas behind the bullet shoots out of the muzzle,
and the muzzle recoils further like a rocket.  This is, again,
conservation of momentum, but in this case is is the gas momentum
out of the barrel that makes the secondary recoil.  Gun manufacturers
make baffles that reduce the flow of gas out of the muzzle to reduce
secondary recoil. Primary recoil cannot be reduced, since it is
simply associated with the forward momentum of the bullet

A Myth Busted

http://www.abc.net.au/science/k2/moments/s1422497.htm

2006\07\23@191502 by olin piclist

face picon face
CSB wrote:
> What's wrong with trying to optimize cost, efficiency and fun?

Nothing.  My comment was because you were making conflicting statements.  If
the goal is to build one yourself regardless of cost, for experience,
education, or fun, by all means go right ahead.  If however the goal is to
maximize productivity (something you also said), then go buy the $300 ready
made solution guaranteed to work off the shelf where someone else has
already paid for the expensive and time consuming development.  There is no
way you're going to build one yourself for $300 unless you value your time
less than $3/hour or so, not to mention the opportunity cost of not having
one until you finish cobbling it together and making it actually work.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\07\23@201037 by CSB

flavicon
On Sun, 23 Jul 2006, Olin Lathrop wrote:

> CSB wrote:
>> What's wrong with trying to optimize cost, efficiency and fun?
>
> Nothing.  My comment was because you were making conflicting statements.  If
> the goal is to build one yourself regardless of cost, for experience,
> education, or fun, by all means go right ahead.  If however the goal is to
> maximize productivity (something you also said)

I didn't mean "productivity" as in "more tests per minute for the least
total cost" ... I wrote "no need to set the gun in a firm support, to line
up exactly with a narrow beam. "

That means that I can just hold the gun and fire, instead of screwing the
thing on and off of a support. That's all.

Of course, making compromises is necessary because of those antagonist
objectives. I know very well I'm not going to keep the butter and the money
(or is it "the cake"? I'm not even sure that's an english expression).



Christian VA2CBW

2006\07\23@203622 by John Ferrell

face picon face
It might make an interesting entry for a contest... or perhaps a magazine
article or just something of interest to post on the web.

John Ferrell    W8CCW
"My Competition is not my enemy"
http://DixieNC.US

{Original Message removed}

2006\07\24@005918 by Gus S Calabrese

face picon face
Has anyone suggested putting one sensor on the gun ( anywhere ) and  
measuring the acceleration of the gun at firing time ?

Gus S Calabrese
Denver, CO
720 222 1309     303 908 7716 cell
Please include and do not limit yourself to "spam2006". I allow  
everything with  "spam2006"  in the subject or text to pass my spam  
filters.



2006\07\24@055023 by Russell McMahon

face
flavicon
face
> ...just don't ask for the
> perfect ... religion, ...

This you can ask for, but only offlist :-) :-) :-) :-) :-)



       RM

2006\07\24@055025 by Russell McMahon

face
flavicon
face
>> What's wrong with trying to optimize cost, efficiency and fun? Is
>> there
>> anything preventing me from wanting an inexpensive home-made
>> solution that
>> works the way I want it to? I thought that was the whole idea of
>> 'doing it
>> yourself' ...

> Quick, cheap, good, inexpensive, marketable, reliable, built using
> info
> from a free mailing list - pick any zero.

1.    Sir, please nominate your second so mine can approach her/him re
terms of engagement.

2.    Do you submit your 10++ posts / day over the last 4 months as
proof of any of the above :-) ?


       R
       :-]


More... (looser matching)
- Last day of these posts
- In 2006 , 2007 only
- Today
- New search...