# Thread: DIY chronograph for measuring bullets??

1. ## DIY chronograph for measuring bullets??

Guys I have searched the web all over does anyone have plans for building your own Chrono I want to measure my pellet guns muzzle velocity.
I found one using a PIC but there is no code or schematic . has anyone ever built one with a prop or basic stamp?? thanks
I bet it would be a very cool project

2. ## Re: DIY chronograph for measuring bullets??

I don't know about the Stamp, but I know that it would be very easy to do with a Propeller.

What sort of sensor were you planning to use to sense the moment that the pellet passes a particular point?

3. ## Re: DIY chronograph for measuring bullets??

If I remember correctly there was a Nuts&Volt project doing that. The sensor part would apply to any micro.
If I can find the issue I'll post it.
Massimo

4. ## Re: DIY chronograph for measuring bullets??

the article I wrote in the June 2009 issue of Nut&Volts(BALLISTIC CHRONOGRAPH) might be what you are looking for - Dave

5. ## Re: DIY chronograph for measuring bullets??

I've wanted to build a chronograph ever since mine broke (friend accidentally shot it with a 9mm, moron).
The software would be really easy on the propeller, but the sensors would be the only thing that may be a bit tricky, but I am sure there are some sensors specifically designed for this use.

6. ## Re: DIY chronograph for measuring bullets??

I did do the math wrong (if you read my previously unedited post) it's logarithmic return, so here we go:

100MHz clock using counters would get 1 ft/s resolution at 10,000 ft/s
80MHz clock using counters would get 1 ft/s resolution at 8,950 ft/s
100MHz clock using PASM would get 1 ft/s resolution at 3,160 ft/s
80MHz clock using PASM would get 1 ft/s resolution at 2,830 ft/s
Oh, and SPIN at 80MHz I estimated would be somewhere around 225 ft/s

There, hopefully I did that math right.

7. ## Re: DIY chronograph for measuring bullets??

Originally Posted by Bobb Fwed
...(friend accidentally shot it with a 9mm, moron)....
Great. Then he's just the guy you'll want to go out drinking with. Check out this:

http://www.nytimes.com/2010/10/04/us/04guns.html?_r=1

8. ## Re: DIY chronograph for measuring bullets??

Thanks guys, Electric I was thinking I could use a PVC pip about 1-2 inch ID and about 12 inches long then put to IR sensors in tube near each end so one IR and one IR sensors then at the other end 1 IR and one IR sensor then I could shoot gun into PVC pipe and somehow program prop to display value os pellet from one IR sensor to the other ?? What do you think??

Oh Camelot how could I get a copy of nut and votls article thank you

9. ## Re: DIY chronograph for measuring bullets??

Article is here: http://nutsvolts.texterity.com/nutsv...06/?pg=36#pg36
The circuit is a little more complicated than I had hoped, but I can't think of any simpler way to do it. The "signal" you are getting as the projectile passes will be very weak, and it needs to be amplified a significant amount. But other than the sensors (which I thought would be the problem), the concept in the article is pretty straight forward.

10. ## Re: DIY chronograph for measuring bullets??

Originally Posted by vettezr1
...I was thinking I could use a PVC pip about 1-2 inch ID and about 12 inches long then put to IR sensors in tube near each end so one IR and one IR sensors then at the other end 1 IR and one IR sensor then I could shoot gun into PVC pipe and somehow program prop to display value os pellet from one IR sensor to the other ??...

In principle that sounds like a reasonable idea, but the devil will be in the details of your set up. Imagine standing in a room with a light bulb 10 feet away. The light bulb is turned on and then somebody tosses a baseball so it crosses your line of sight half way between you and the bulb. For an instant the light bulb will be eclipsed, but the room will still be alit by the light of the bulb. Similarly, if your IR emitter and sensor aren't designed very well, then your sensor will still detect light bouncing around inside the pipe even though the emitter itself might be eclipsed. So your emitter and detector need to create a beam of detection that is very narrow. And your pipe needs to be lined with some sort of IR absorbing material, preferably something like felt or whatever with a flocculent surface. The pellets, I'm guessing, aren't very big, so you'll probably have a heck of a time lining up your shots to cross the light beams. I'm guessing pellets at 1000 ft/sec, so one foot gives you about a millisecond of time. I suppose the Prop could resolve that without too much trouble.

But, as I said, the details of your construction will be what matter most.

11. ## Re: DIY chronograph for measuring bullets??

Bob thank you sir, Electric you are correct I built a bread board version the pellets are 177-22 caliber very small and travel at around 650 FPS-1200 FPS with special alloy material. FWIW the idea is sound but in real world results
I can not get the detectors to respond that fast I had some luck with a smaller ID pipe to keep the projectile in the path of IR devices but then I ended up hitting one end of the pipe .. Bob I am going to give your desgin a shot but I am wondering if I might need some kind of RC trigger another problem is the gun will emit a cloud of compressed air into the pipe changing the lighting significantly I see some ideas posted on the web but nothing I have been abel to replicate Thank you guys if I get something working well I will post it in finished projects Oh I think I will have to use the prop I was trying it with stamp BS2 to be exact but its just not fast enough or I need a better circuit

12. ## Re: DIY chronograph for measuring bullets??

Originally Posted by vettezr1
...Bob I am going to give your desgin...
Not to take credit, where it's not due: it wasn't my design. the link I posted is the Nuts & Volts article you were asking about.

13. ## Re: DIY chronograph for measuring bullets??

@vettezr1

What you need for this project is:
1 - a laser diode and 2 mirrors to create a "light curtain" at each end
2 - possibly a photodiode detector rather than a phototransistor (for higher speed)
3 - a light baffle at the entrance to reduce background light
4 - a peak detection circuit that produces an output pulse for fast light level changes

14. ## Re: DIY chronograph for measuring bullets??

Originally Posted by kwinn
@vettezr1

What you need for this project is:
1 - a laser diode and 2 mirrors to create a "light curtain" at each end
2 - possibly a photodiode detector rather than a phototransistor (for higher speed)
3 - a light baffle at the entrance to reduce background light
4 - a peak detection circuit that produces an output pulse for fast light level changes
kwinn,
are you suggesting that he try to detect light reflecting off the pellet? rather than the eclipse of the light source? If so, that's an interesting idea. You think the pellets are reflective enough?

15. ## Re: DIY chronograph for measuring bullets??

No, I don't think there is enough light reflected from a pellet to make that practical. What I had in mind was a narrow beam of light that was reflected back and forth several times between two mirrors before arriving at the detector. The beam would travel down at a small angle each time it was reflected somewhat like the raster scan on a tv picture tube.
This would make the aiming less critical and produce a better signal.

16. ## Re: DIY chronograph for measuring bullets??

Originally Posted by kwinn
...What I had in mind was a narrow beam of light that was reflected back and forth several times between two mirrors before arriving at the detector....
I can see how that would work, but I would be somewhat concerned about how to accurately and rigidly position the mirrors. I think each mirror would need 2 degrees of freedom to get things just right. I've been looking at some laser line generator lenses, but these things cost a heap of money. \$155-ish.

How about using two light guides made out of acrylic sheet? He could figure out the pellet flight path using paper stretched over each end, polish the edges of both the emitter and receiver sides of the acrylic light guides, space them fairly close together around the holes in the paper, align them/square them up using a removable sheet of acrylic as a guide, then blast away. I'm not sure how efficiently IR goes through acrylic, however. He might have to change to an optical color. But maybe light guides would help cut down on the random reflections?

17. ## Re: DIY chronograph for measuring bullets??

What I had in mind was more like the attached diagram. The laser beam would reflect between the parallel mirrors in a tight enough pattern that the pellet could not pass without breaking or at least blocking a large portion of the beam.

The hard part would be alignment, but if a visible wavelength was used it should be doable.

18. ## Re: DIY chronograph for measuring bullets??

Originally Posted by vettezr1
the pellets are 177-22 caliber very small and travel at around 650 FPS-1200 FPS
The challenge here will be the narrow aperture times, ~14us, so easiest is to
find a Logic output interrupter,
(rather than a Transistor output, which will have saturation problems)
and it turns out Digikey seem to have just the thing :

5mm:
http://media.digikey.com/pdf/Data%20...1A58HRJ00F.pdf
10mm:
http://media.digikey.com/pdf/Data%20...1A58HRJ00F.pdf

with typical delays of 3us/5us , and the Logic output feeds straight into a Logic Pin.

You could start with two, and then see if one can give enough precision ?
Two would give same-edge action, and so be more tolerant of sensor variations, and
measuring both /-/ and \-\ would further average errors.