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Big thanks to Technician1002 for his help.
For this I used a dynamic Akai ADM-20 microphone plugged in to my Dell laptop and I used Audacity to record the audio and find out the velocity.
Originally I used a condensor microphone which was no good. To get good audio, you really need to use a dynamic microphone or have some sort of mixer to change the recording settings and bypass the computer soundcard settings.
I set my targets 5 meters away from the muzzle and placed the microphone in the middle at 2.5 meters. I also faced the microphone away from the muzzle and toward the target to get better recordings. This method of chronographing isn't very difficult though it can be harder to setup as you need a target with which the projectile can be heard impacting or a projectile that will do this. You also need to be at a fixed distance and be wary of your surroundings to avoid echo or bad accoustics.
Big thanks to Jimmy101 for his help.
I tried this method mainly because I thought it would be interesting and a fun project, it was. For this you'll need two phototransistors. I picked the only clear phototransistors available at my local JayCar store. You'll also need something to mount these to that shields most of the phototransistor from light and keeps them at a fixed distance apart. Jimmy101's website page above was very helpful, so be sure to check it out. My phototransistors are mounted in wood with only the top of them open to the light. They are then mounted in a thin metal rail which is fixed to a flat piece of wood to stop it from being blown away. My circuit is wired in parallel with no resistors and connected to a stereo channel 3.5mm audio plug. I also used Audacity to record with.
I found this method slightly better for my purposes as I am limited in shooting space and this mehtod only requires that the projectile leaves the barrel, no target is needed, only something to stop the projectile. It will also give you a higher velocity reading because you can measure the muzzle velocity instead of the velocity from a distance. I have a very basic knowledge of electronics, yet I was able to construct this so don't be put off if it sounds difficult.
This chronograph is also very cheap to construct ($5) and easy to build. Only problems I've had with it is the lighting, it wont work under fluorescent lights as they turn on and off rapidly which will interfere with the signal. Some people use LEDs to enhance the spike generated when the phototransistor is blocked from light, I found this a bit difficult so instead I just use a cheap 500w flood lamp which does the job nicely. Though the chronograph will work great (large, clear spikes) outside as long as it isn't too dark or cloudy. I found it even worked in overcast weather fine.
Anyway, here are some results of these chronographs compiled in to a video along with some photos below:
nice work mate and a good write up. I am liking the second method alot more, seems to be more accurate...
It should work in any lighting, as long as there is some light... All you need is constant light, (so dont use this next to a strobe, remote controls fluro or energy saving lamps... Dont they use PWM to control brightness?? )when you use more light it will just make the spikes bigger and easier to see.
I think it would be a topps idea if there was a program or at least some kind of way to automate the process... Maybe using a program like auto hotkey, ratt or scar
Also, i have to say that jaycar is a godly shop... The one in act is rly awesome and the staff actually know what they are talking about! Not like that dicksmiths electronics... "hello i am looking for a transistor" ".....um like one of them old time radios?? We dont sell them here" *facepalm*
Me: "Hello i am looking for a phototransistor"
Them: "You want to put photos on a flash drive?"
Me: "No, a PHOTOTRANSISTOR"
Them: "A photo what?"
Me: "...transistor. One word."
Them: "Oh sorry, our electronics guy isn't here today..."
By the way, there is a program called SoftChrono which automates the audio chronograph method. I couldn't figure it out though.
what is that guy doing working in a shop which 50% electronic components!!
yeah, when i installed that one it came up as spywear... so it was gone in a matter of seconds
Looks good. The phototransistors I've seen all respond well over the visible spectrum (the ones labeled IR phototransistors). Haven't actually used them with AC lights (worklamps, etc.), but I'd think that a worklamp would oscillate as well (though I may be wrong) at 60hz.
But if it's working it's working. Good job!
Yup you're right, there is some noise but nothing compared to a fluorescent. Though the muzzle blast seems to be defeating what the light is fixing because the mist interferes with the peak/spike, so I need to sort out some muzzle brake thing. I've removed the "stock" on the V.A.L which should reduce some of it.
Those would be the darker coloured ones? I read somewhere they only work well with IR and not so well with other light, I'm probably wrong.
IIRC, it's the air condensing. I guess you could just call it steam. The gas (air) heats up when it is compressed and when you release it in to room temperature it cools.
i think its 50hz
edit: i googled it and the use use 60 and in oz me use 50hz
now i look like a douche
Last edited by Crna Legija on Wed May 19, 2010 5:56 am, edited 1 time in total.
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yep 50 here 60 in US i think
Great video and work.
In Audacity there is another view to fill the screen and perhaps see it better.
To get technical, there are 2 power peaks in one cycle, one positive and one negative. On 60HZ power the flicker rate is 120 times/sec.
It can be seen in an incandecent bulb in this slow motion video.
The incandescent bulbs have a weak flicker due to the thermal mass.
While the power to your houses may have a 60Hz cycle, florescents do not anymore. With the old magnetic ballast, they would cycle with the power to the house, but the new electric ballasts cycle much faster. The cycle somewhere in the 30k-50k hertz range. Anyone who complains about the flicker of compact florescents is either full of s*** or using 5-10 year old technology.
In other news, I was working on my stat project, which involves measuring the speed of various projectiles, at various ranges, but we weren't finished by the time the sun set. The chrony started reading "LB" for low battery, but really the problem was it was getting too dark. We hung up 3 100w incandescents, shining down on the sun screens, and were able to keep shooting well into the night.
This was using the standard shooting chrony though, not a home made one.
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It is true that many CF bulbs use a high frequency inverter. It is not true that all CF bulbs are free of line frequency flicker. Due to the heat and failure rate of electrolytic capacitors, many CF bulbs to save weight and size in the base no longer use electrolytic capacitors to keep the bulb lit during the polarity crossing, so many dim to very low power (low output) at the 120 hz rate. To prevent short life due to re-strikes, most do not go completely out on the voltage reversal. This makes some bulbs dimmable by phase controlled dimmers and some are marked as dimmable. Those with filter caps in then when place on a dimmer will go out until strike voltage is reaches and they will strobe at low voltage resulting in early failure.
It is a mis-conception that because a CF bulb uses a high frequency inverter that is it devoid of low frequency filicker. Is some bulbs this assumption is false.
This video shows some bulbs exhibiting this flicker. After they start the flicker is less pronounced. Some bulbs have heavier flicker. Most have low to no low frequency flicker.
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