# DIY Chronograph for $1



## Veni Vidi Vici (Jan 23, 2011)

OK, well maybe it needs some more testing. That's where you guys come in. 

I saw this on instructables and I had to try it out.

Here's the full story of what I've done.

I have not shot my bow through a real chronograph yet, so first I had to get an estimate of my speed. My bow is rated at 308 fps at 60# and 29" draw with a 300 grain arrow. I went to this online calculator and used it to back calculate what my 70#, 30", 350 grain IBO rating would be. Turns out the equivalent rating is ~326fps. Now, I actually shoot at 60#, 28", and 396 grains. Using that same calculator, my estimated speed is around 266 fps.

Back to the DIY chrony ....

Per the above instructable, I downloaded and installed the free sound software audacity. This software does a ton of things, but the feature I needed was recording from a microphone and displaying the graph of the sound track.

At first I tried the microphone that is on my laptop, but I didn't get good results with that. It was easy to see when the arrow hit the target, but it was difficult to pick out the right point during the shot. So I bought a $1 microphone at the dollar store. As luck would have it, that seems to work much better.

I carefully measured the distance from the target to my bow. Then I placed the laptop halfway between the two. It makes the math easier if the microphone is the same distance from the target as it is from the bow. I started the recording and took a shot. Then, using the features in the audacity software, I located the time when the arrow hit the target. This is pretty easy, because it is a very distinct spike. Then I had to play with which point during the shot portion of the soundwave to use as the beginning time. Once I had the two times, I subtracted the lowest one from the highest one and divided the distance by that time. Voila! I had the average speed of my arrow over that distance! 

I'm pretty consistently able to use this sound technique to measure within +/- 4 fps of what the archery calculator program says it should be. When I get a chance, I'd like to shoot through a real chrony and see if there is a different point in the sound track I should pick for the start time.

If you guys feel like playing around with this, and you know your "true" chrony speed, give it a shot (pun intended!) and report back with your results.

BTW, the audacity software might have other uses, too. You could probably use it to tell how loud your bow is with/without silencers, etc.


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## Camo-omega (Jan 18, 2011)

that's a really awesome idea. definitely alot of thought put into this. where did you get this program and how much did it cost if any? I'm not so much interested in the diy crony cause it's a tid bit too much math for me but measuring how much sound the bow creates could be very helpful


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## Veni Vidi Vici (Jan 23, 2011)

See my OP. It's free, and there is a link to it. As far as the math goes, as long as you put you microphone halfway between the bow and the target the speed is the distance to the target divided by the time it takes for the arrow to get to the target.


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## SMBHUNTER (Oct 12, 2010)

Wow great idea! Does the graph use db's as its measurement? I am very interested in checking out what kind of noise my bow is producing at the release point.


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## Veni Vidi Vici (Jan 23, 2011)

OK, here are some pictures of how to do this to get you started.


I've circled the portion of the recording that is the shot and impact. I also circled the input volume control. Setting this to .5 worked best for me. This might vary with different microphones or distances from the mic to the bow/target.













Drag your cursor to select the shot portion of the recording.













Click on Fit Selection in Window. I also grabbed the bottom edge of the track window and stretched it vertically.













Left or right click on the bar on the left to scale the vertical up or down. Also, use the zoom + and zoom - to stretch the horizontal until your display is similar to this one.













This is where the action is. The line on the left is where I chose to click for my start time. The oval at the bottom shows the time associated with this position. It's pretty obvious where the sound of hitting the target starts. I entered these values in a spreadsheet and calculated the speed. The spreadsheet has results from two different recording attempts on it. You can see that it's not too hard to get consistent results.













The tricky part of this whole thing is identifying which point represents the launch time. Since I already had an estimate of my speed (I want to use a real chrony soon to verify this), I was able to identify that the first part of the launch sequence is noise that occurs during the launch BEFORE the arrow is off the string. I'm assuming that the noise climbs to its peak after the arrow is clear of the string. This all seems reasonable, but if more people (who already know their speeds) can try this out we can probably learn more about how to select the start point. The measuring system seems very consistent, but the interpretation part is what needs some work.


The question was asked about whether the output can be displayed in dB. The answer is, yes, but I'm not sure how to interpret the display. If you click on the Audio Track pop-up menu, you get this menu:










You can select Waveform dB, and the graph will change. But the scale is from 0 to a large negative number, so I'm not sure how to interpret this.


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## CandianQuest (Mar 31, 2010)

well of course it will be a bit slower than what the calculator says cuz a chrono uses the first foot or couple inches in front of the bow to tell you the speed, and all arrows slow down over distance (force friction with the air) it will slow down, resulting in a slightly slower reading than what a chrono would give you, but it still will be really close.


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## alleycatdad (Aug 15, 2010)

Can the software record in stereo? If so, could you get some longer mic cords and actually place one near the bow and the other near the target? Shouldn't cost more than a few bucks for cables and plugs if you make em yourself.


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## TJK (Dec 2, 2010)

I've use audacity before and I think this would great. I already made the spreadsheet and typed some random numbers in and it seemed to work I’ll be trying it out soon. Thanks for the great idea.


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## Veni Vidi Vici (Jan 23, 2011)

alleycatdad said:


> Can the software record in stereo? If so, could you get some longer mic cords and actually place one near the bow and the other near the target? Shouldn't cost more than a few bucks for cables and plugs if you make em yourself.




I believe it can, but your hardware has to be able to support multiple input channels. My laptop doesn't.


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## alleycatdad (Aug 15, 2010)

Duh! Didn't think of that. What about capturing with, say, a video camera or a stereo digital sound recorder w/mikes and importing it? Another step, I know...if you lived close I'd loan you my recorder to try, but I suspect youdon't...

S


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## TJK (Dec 2, 2010)

Hey guys I just did some testing with this. Only I used my cell phone (not a smart phone). I just used the voice record and then put it on my computer (I don’t have a laptop) audacity would not open it so I had to use Switch file converter (free) to convert it to mp3 and then I used audacity.


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## Veni Vidi Vici (Jan 23, 2011)

Hey guys, I figured out how to do all of this without sound, but still using a laptop and audacity. The new way is much more like a true chrony as you don't need much distance so drag won't be a factor. I started a new thread for that one  here.


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## TJK (Dec 2, 2010)

I went to the pro shop here in town and shot through there chronograph it said I was shooting 149 fps I shot 6 shots using this method and got an average of 142 fps. That is close enough for me and no money invested. I also have and excel file that i made that you can put in the nubers and it does all the work for you but i don't know how to upload it


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## Veni Vidi Vici (Jan 23, 2011)

That's great, TJK. It's nice to have some confirmation on this, and that was a great idea using your cell phone to record. Check out my other thread on how to improve this method just by adding some wire.


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## droppixel (Nov 5, 2010)

This is awesome and if it weren't dark outside I would be out trying it right now! Just got the software loaded up, but it isn't showing me the times of the cursor selections. Going to have to fiddle with it a little and get it all figured out. This should be fun.


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## Veni Vidi Vici (Jan 23, 2011)

The times should show up down on the bottom bar towards the left when you click on the graph. Make sure you check out my other thread for an improved version!


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## droppixel (Nov 5, 2010)

Don't have access to an external mic that I can use for the second option. Did a few runs with my mbp and was getting pretty good sound pickup. If I am analyzing the waveforms correctly I am seeing in the 290s which would put me just about with with the calculators I have seen. Going to try to get on a chrono later today and see if this is close to what the chrono says. I'd be rather happy and surprised if it were.

Thanks for sharing the idea, this is pretty cool. If I can pick up the mic jack I will probably give the other option a try as well. Might have an older one hidden in my closet, but not totally sure.


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## Veni Vidi Vici (Jan 23, 2011)

droppixel said:


> Don't have access to an external mic that I can use for the second option. Did a few runs with my mbp and was getting pretty good sound pickup. If I am analyzing the waveforms correctly I am seeing in the 290s which would put me just about with with the calculators I have seen. Going to try to get on a chrono later today and see if this is close to what the chrono says. I'd be rather happy and surprised if it were.
> 
> Thanks for sharing the idea, this is pretty cool. If I can pick up the mic jack I will probably give the other option a try as well. Might have an older one hidden in my closet, but not totally sure.


Be sure and post your results!


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## jim p (Oct 29, 2003)

Which version of audacity are you using?


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## Veni Vidi Vici (Jan 23, 2011)

jim p said:


> Which version of audacity are you using?


v. 1.2.6 (latest version)


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## 20ftup (Mar 19, 2007)

Any bets on who puts an arrow into their laptop??? Sounds like a fun thing to try tho


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## 09Dreamseason (Feb 11, 2010)

20ftup said:


> Any bets on who puts an arrow into their laptop??? Sounds like a fun thing to try tho


I'm currently building this and going to power the coils on his "improved version" and I thought about that same thing........so I spent a few bucks more and got a 6 foot audio cable at Radio Shack to put my laptop on a table next to me from where I'm shooting. The 6 foot audio cable costs $7 and I picked up an audio jack to solder the coiled wires to in order to have a clean system to plug the audio between the chrony and my laptop audio jack! I'll post pictures in the new "improved" thread when I have it completed.


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