My previous DIY Chronograph thread gave all of the details on the software, so I'm not going to go over it again here. The problem with that method, as I explained on that thread, is determining exactly when to select the point on the soundwave to represent your arrow's launch. The bow makes some noise throughout the entire launch sequence, so picking exactly when the arrow comes off of the string is just a guess.
I started thinking, "What if I could detect the launch without using a microphone?". Here's what I have now.
![Image]()
I took some extra invisible fence wire I had and wound two coils in series. The coils are about 10" in diameter, 16-17 turns each. I mounted them (that's what duct tape is for) to a board and measured the distance between them. Then I took the ends of the wire and attached them to a microphone jack (from the same $1 dollar store mic I used originally).
When an arrow is shot through the coils, the software detects this very precisely. Since the arrow is now passing through two coils spaced apart, I can see each event. Using the audacity software to record the shot and measure the time between the events is what makes this ultra-cheap chrony work.
Here's a screenshot of the initial recording. There are a couple of things to notice. First, the microphone input slider is all the way to the right this time. The coils don't generate much of a signal, so you need everything you can get. Second, after I started recording, I left-clicked on the 0.00 on the left bar multiple times to zoom in as much as possible. I then took the shot and hit stop. The small blip on the graph is the shot. I selected this area and used the Fit Selection in Window button to blow it up. It took a couple of times and I also dragged the window larger, but I ended up with a good view of the two blips that are the arrow passing through each coil.
![Image]()
![Image]()
![Image]()
After a few times, this is the view I ended up with. If you notice that the second blip is flipped compared to the first blip, that is because I wound my second coil in a different direction than my first coil. This was by accident, and it doesn't effect the end product.
Because the blips feather in and out at each end, I decided that the most consistent place to use as a time selection was the middle of the straight diagonal connecting the high and low humps of each blip. Here's the first selection:
![Image]()
And here's the second selection, along with my spreadsheet showing the results of 5 consecutive tests. Not too bad, huh! :teeth:
![Image]()
I started thinking, "What if I could detect the launch without using a microphone?". Here's what I have now.
I took some extra invisible fence wire I had and wound two coils in series. The coils are about 10" in diameter, 16-17 turns each. I mounted them (that's what duct tape is for) to a board and measured the distance between them. Then I took the ends of the wire and attached them to a microphone jack (from the same $1 dollar store mic I used originally).
When an arrow is shot through the coils, the software detects this very precisely. Since the arrow is now passing through two coils spaced apart, I can see each event. Using the audacity software to record the shot and measure the time between the events is what makes this ultra-cheap chrony work.
Here's a screenshot of the initial recording. There are a couple of things to notice. First, the microphone input slider is all the way to the right this time. The coils don't generate much of a signal, so you need everything you can get. Second, after I started recording, I left-clicked on the 0.00 on the left bar multiple times to zoom in as much as possible. I then took the shot and hit stop. The small blip on the graph is the shot. I selected this area and used the Fit Selection in Window button to blow it up. It took a couple of times and I also dragged the window larger, but I ended up with a good view of the two blips that are the arrow passing through each coil.
After a few times, this is the view I ended up with. If you notice that the second blip is flipped compared to the first blip, that is because I wound my second coil in a different direction than my first coil. This was by accident, and it doesn't effect the end product.
Because the blips feather in and out at each end, I decided that the most consistent place to use as a time selection was the middle of the straight diagonal connecting the high and low humps of each blip. Here's the first selection:
And here's the second selection, along with my spreadsheet showing the results of 5 consecutive tests. Not too bad, huh! :teeth:
