# Diy Chronograph



## MAV (Mar 18, 2012)

Geko posted a DIY chronograph using free Audacity software (thanks Geko). At work during lunch I found a archery message board where several people made there own chronograph. This was so simple I thought it should be shared, my plate is full until after Xmas but this is on my to do "A" list for sure. Instead of the microphone these guys used 2 coils of wire (the bigger the loop, the more wire), one guy used the invisible dog fence wire another used some of that lacquer coated motor winding type wire. They made 2 loops about 20 winds each and placed them on a board a known distance apart, spliced the wires into a microphone input jack and plug into a PC. Now they shot a magnetized field tipped arrow through the loops and recorded it on the Audacity software. Simple. One guy even wrote another software program just for this chronograph. Input is input, so if you pass a magnetized ball bearing through a coil of wire it will create input for the software. You pass the same steel magnetized slingshot ammo past a second coil of wire over a accurate known distance you now have a chronograph. You have to magnetize your BB's, no big deal, if you miss and hit the coils, no big deal. Do a search and check it out, let us know how you do! I'm booked up right now, to many pokers in the fire.

Mark


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## Hrawk (Oct 25, 2010)

Hall Effect Sensors (what you have described above) do work quite well but can be a bit limited by the needed magnetic flux and size of the coils.

Another simpler way to do this is using a pair of photo diodes. These can be picked up for a dollar or two each.


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## MAV (Mar 18, 2012)

Hrwak, all I would need is my net-book (8 hr batt life) and the said chronograph (2 loops on a board) to rock. I read a post about the photo diodes and the width of the reading ability of the one I read about was 5mm. 5mm! You had to interrupt the path by at least 2.5 mm to get a reading. They used it on bench rest rifle. I aint down to 5mm yet. This is a hoop of wire, you make a hoop, hook up your Fluke meter and gravity drop a magnetized ball bearing through it, if you get a reading put it together and go for it. If no reading, wrap more and try it again.

Mark


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## MAV (Mar 18, 2012)

Sorry, a Fluke meter is a slang for a multimeter.


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## Hrawk (Oct 25, 2010)

It's all good, I know what a Fluke is. Still to this day amazes me that Phillips create at least one good product.

You do not have to use focused phototransisters though. The ever populour Shooting Chrony uses a gang of 5 phototransisters as it's detection mechanism. This gang of 5 gives a detection window of about 100mm wide at approx 100mm above the sensors.

When hooking these up to an audio recording device such as your laptop / notebook, you are not looking for a digital singnal, simply a varience in the amplitude of the waveform, just like using the hall effect sensors or 'loops' as you call them.

The above pic is simply the first one I found that showed the basic wiring.

However you choose to go, either method will work.


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## MAV (Mar 18, 2012)

Thanks Hrawk, great conversation! No insult intended about the Fluke definition. I'm sure many here never heard of a "Fluke" as it is a slang. I guess the real proof is a side by side test for accuracy. Not scientific, but take for granted the store bought F1 or what ever is correct and see how close the home-made and free software comes. Interesting...

Mark


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## Imperial (Feb 9, 2011)




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## AJW (Apr 24, 2011)

MAV & Hrawk - What a great posting !! Very informative, very interesting. Since most people don't have a chrony this should be a popular DIY project. Thanks guys, my hat is off to you.


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## Hrawk (Oct 25, 2010)

You'll find that the 'home made' chronographs using an audio card in a PC can be VERY VERY accurate indeed based on the sampling speed of the hardware.

Even the most basic audio cards, when put into mono mode, can handle 96,000 to 115,200 samples per second !!! (which is actually higher/faster than some chronographs).

You will also get more accurate results from your sensors (coils) being spaced further apart.


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## MAV (Mar 18, 2012)

OK, That's it. I cant take it anymore. I'm building one Saturday. Have nothing for a side by side test, but I'll post what ever happens unless a fellow member beats me to it and my post would be rendered redundant.

Mark


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## Henry the Hermit (Jun 2, 2010)

I started measuring speed with a Netbook, microphone and two pieces of paper spaced 10 feet apart, using Audacity to measuring the time between sound events. I've never compared the results directly with my Chrony, but early readings are very close to what I get now with the Chrony. The only problem with that method is correctly determining the exact start of each audio event.

BTW, I had 2 Fluke 77s, both of which went TU after about 3 years. My Fluke 73 has been going strong since 1996 and I still use it frequently.


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## MAV (Mar 18, 2012)

My Father is 85 years old and has a old Simpson, he said I can have it... When he is done with it. LOL! The Simpson still works great!

Mark


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## MAV (Mar 18, 2012)

I wonder if the coil method would give better results for determining the events?


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## Hrawk (Oct 25, 2010)

MAV said:


> I wonder if the coil method would give better results for determining the events?


The key to your accuracy here is making both coils as identical as possible so they both display an almost identical waveform on your capture device. This makes it much easier to accurately calculate the time between events by selecting the same point in each waveform. In a good setup, these will both resemble sharp peaks in the graph.

Due to the design, the coils are likely to pick up a lot of background interference or RFI. The quality of the coils will dictate the signal to noise ratio. The higher the better.


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## Henry the Hermit (Jun 2, 2010)

MAV said:


> My Father is 85 years old and has a old Simpson, he said I can have it... When he is done with it. LOL! The Simpson still works great!
> 
> Mark


The Simpson 260 was the best multimeter available when I got into electronics in 1961. It was first manufactured in the 1930s. I doubt you can find a better analog meter even today. Alas, low voltage solid state development made it obsolete for technical use.


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## MAV (Mar 18, 2012)

This is great! I'll build the chronograph and test Saturday. I'll post, then we can pick it apart. Still with out a "store bought"" chronograph for a benchmark I cant tell a level in accuracy. I'll build it, try it out, and we will just have to crunch from there.


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## Hrawk (Oct 25, 2010)

Sounds great.

If you get the chance, could you make up a build log / tutorial as you go for the benefit of others who might want to have a go making one ?


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## MAV (Mar 18, 2012)

Hrawk said:


> Sounds great.
> 
> If you get the chance, could you make up a build log / tutorial as you go for the benefit of others who might want to have a go making one ?


Yes. I will.

I was thinking, 7/16 steel. Say the coils are 2 feet apart, set it vertical and drop the steel BB 1 foot above the first coil. The mathematical formula for gravitational acceleration would tell me what speed the BB should be when traveling between the 2 coils. This has a possibility to calibrate or verify the accuracy of the chronograph. I have a brother who is a math teacher, I'll toss this at him and see if he can give me a FPS between the 2 coils, then I'll do actual test and see how close they are. This is going to be a blast!


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## MAV (Mar 18, 2012)

Hrawk said:


> Sounds great.
> 
> If you get the chance, could you make up a build log / tutorial as you go for the benefit of others who might want to have a go making one ?


Yes. I will.

I was thinking, 7/16 steel. Say the coils are 2 feet apart, set it vertical and drop the steel BB 1 foot above the first coil. The mathematical formula for gravitational acceleration would tell me what speed the BB should be when traveling between the 2 coils. This has a possibility to calibrate or verify the accuracy of the chronograph. I have a brother who is a math teacher, I'll toss this at him and see if he can give me a FPS between the 2 coils, then I'll do actual test and see how close they are. This is going to be a blast!


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## Hrawk (Oct 25, 2010)

Average velocity 







 of a falling object that has travelled distance 







 (averaged over time):











Instantaneous velocity 







 of a falling object that has travelled distance 







:











Or just use this website : LINK


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## MAV (Mar 18, 2012)

Thanks Hrawk, I'm still going to see what my brother can tell me. The fomula you posted works in a vacuum. At risk of making this more complex then necessary I would like to see if he can figure the air resistance at my altitude and give a little closer target number to work with. I need to Google and find the average air density at 800 feet above sea level and then I think I have every thing needed to crank out the target number.

Mark


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## MAV (Mar 18, 2012)

Nothing, got nothing. Made a coil, have continuity, through coil, coil picks up a magnet passing through on a multimeter, nothing when I plug it in my net book and try it with audacity. It is not seeing it. Dang, this sounded promising.


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## MAV (Mar 18, 2012)

Messed around some more, it's not seeing the input. The $100 F1 Chrony looking better all the time. Dang.


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