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Homebuilt Phototransistor Chronograph

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Homebuilt Phototransistor Chronograph

Unread postAuthor: boyntonstu » Wed Nov 18, 2009 1:20 pm

[youtube]http://www.youtube.com/watch?v=0CTSGCbYAWk[/youtube]

A FEW POINTS:

1. Start Audacity recording and note the time of the shot on your watch.
Go to your PC and stop recording a minute later.
Look back one minute for the shot information.

2. AFAIK This chronograph working 100 feet from the PC is the furthest that I have seen.

3. PIP #1 is smaller than #2 because the light bulb is too bright.
(I broke a smaller bulb and I used what I found in my shop drawer)

4. The circuit is very simple, and consists of 2 phototransistors, wire, and a 4k resistor.

BoyntonStu
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Last edited by boyntonstu on Wed Nov 18, 2009 3:10 pm, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 18, 2009 1:42 pm

Quite a ghetto setup but it seems to work, perhaps you ought to shield the bulbs and photodiodes better so you can avoid the whole timing affair.
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Unread postAuthor: boyntonstu » Wed Nov 18, 2009 1:49 pm

jackssmirkingrevenge wrote:Quite a ghetto setup but it seems to work, perhaps you ought to shield the bulbs and photodiodes better so you can avoid the whole timing affair.


The 100 feet of wire picks up crap.

I am using phototransistors not photodiodes.

Timing 1 minute is simple enough.

Notice the lack of noise at the time of the shot.

Ghetto is my middle name.

I would rather build it for $10 than buy it for $10.01.

It gives me pleasure to make something the way I want it to be.
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Unread postAuthor: Technician1002 » Wed Nov 18, 2009 2:09 pm

Well done. To make the blips easy to find. I insert the steps;
View,
Fit in Window.
That saves scrolling to search.

Effect,
Amplify.

This makes the tallest blip as tall as you want it and easy to find. Using the default gain will bring the blip all the way up to 0db. Using a lower setting can keep the peak from 100%.

Highlight the peaks with the cursor and then;

View,
Zoom in.

Makes finding the event very simple without searching. It stands out like a sore thumb.
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Unread postAuthor: boyntonstu » Thu Nov 19, 2009 12:33 pm

Image

Have Chrono, will Travel (100 feet).


Neatened things up a bit and added cord storage.

I may add a sight at the top of the wood towers that hold the PVC.

My next maybe project; run everything off an ac/dc adapter.
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Unread postAuthor: jimmy101 » Thu Nov 19, 2009 1:22 pm

As long as you are using the 100' of wire you can drop the light bulbs. Just point the whole thing at bright sky. More than enough light there.

Are you using the line input or the MIC input for the PC? If you use the MIC input you can omit not only the light bulbs but the battery/power supply, and probably the resistor, as well. (A MIC input usually supplies 2.5V at about 1mA, which can be used to operate the phototransistors.)

You can also short across one, or both, of the photo transistors with a DVM and get a reading of just how big your voltage swings are. Note the reading on the DVM, then put your finger in front of one of the gates and note the new voltage. The difference it the voltage swing (duh :D ).

In my experience a few tens of millivolts is all that is needed, though bigger swings are always nice. Smaller swings can also be used but eventually noise starts to be a problem. The DVM lets you get an idea if everything is setup correctly without having to start the recording, walk to the gun, do a shot then walk back to the PC ...

If you do convert to a wall wart power supply you may have problems with there being too much noise in the signal. Wall warts don't give the cleanest voltages and the fluctuations will show up in your recordings, probably as a very ugly 120Hz signal (from 60Hz mains). A couple big caps might be needed or you'll need a very big swing in the signal.

Point your rig at a 120VAC light and get a recording of an incandescent light acting as a rectifier and frequency doubler. (Nice thing about the sun is it doesn't blink.) Point a TV remote at one of your detectors and record the remote's signal.

Changing the bulbs to 3V flashlight bulbs and running the whole thing off a couple 1.5V batteries might work better than the wall wart, and it omits the need for 120VAC or a large 12V battery.
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Unread postAuthor: boyntonstu » Thu Nov 19, 2009 3:06 pm

jimmy101 wrote:As long as you are using the 100' of wire you can drop the light bulbs. Just point the whole thing at bright sky. More than enough light there.

Are you using the line input or the MIC input for the PC? If you use the MIC input you can omit not only the light bulbs but the battery/power supply, and probably the resistor, as well. (A MIC input usually supplies 2.5V at about 1mA, which can be used to operate the phototransistors.)

You can also short across one, or both, of the photo transistors with a DVM and get a reading of just how big your voltage swings are. Note the reading on the DVM, then put your finger in front of one of the gates and note the new voltage. The difference it the voltage swing (duh :D ).

In my experience a few tens of millivolts is all that is needed, though bigger swings are always nice. Smaller swings can also be used but eventually noise starts to be a problem. The DVM lets you get an idea if everything is setup correctly without having to start the recording, walk to the gun, do a shot then walk back to the PC ...

If you do convert to a wall wart power supply you may have problems with there being too much noise in the signal. Wall warts don't give the cleanest voltages and the fluctuations will show up in your recordings, probably as a very ugly 120Hz signal (from 60Hz mains). A couple big caps might be needed or you'll need a very big swing in the signal.

Point your rig at a 120VAC light and get a recording of an incandescent light acting as a rectifier and frequency doubler. (Nice thing about the sun is it doesn't blink.) Point a TV remote at one of your detectors and record the remote's signal.

Changing the bulbs to 3V flashlight bulbs and running the whole thing off a couple 1.5V batteries might work better than the wall wart, and it omits the need for 120VAC or a large 12V battery.


Thanks, good suggestions.

I made it out of my junk pile inventory.

It is basic, but it works fine.

Unfortunately, my Dell laptop mic input does not supply dc.

Have you uploaded a photo of your chrono?


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Unread postAuthor: Technician1002 » Thu Nov 19, 2009 4:04 pm

A quick note on using soundcard mic inputs. To reduce background noise, many sound cards heavily filter the input to speech frequencies. this can filter out high speed events and round them out, so instead of getting a pop with a sharp easy to measure risetime, you get a rounded molehill waveform. Avoid the mic input on most sound cards.

Use the audacity amplify function instead. It will preserve the rise time.

See this sound card page for more info on this.
http://www.epanorama.net/documents/pc/soundcard_tips.html
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Unread postAuthor: jimmy101 » Fri Nov 20, 2009 2:25 pm

boyntonstu wrote:I made it out of my junk pile inventory.

It is basic, but it works fine.

Unfortunately, my Dell laptop mic input does not supply dc.

Have you uploaded a photo of your chrono?

BoyntonStu

http://www.inpharmix.com/jps/Jims_chrono.html
Your MIC input doesn't supply DC? That's pretty unusual and means that the typical electret (sp?) mic will need a battery. Usually you need a stereo plug to use the MIC input. The tip of the jack is the audio, the base is the common/ground. The ring is either nothing or ~2.5V at ~1mA. Some MIC inputs put the voltage on the tip, in which case the tip is both the power source and the signal line. If that is done then the ring doesn't do anything. There are probably other setups as well. Unfortunately, the audio ports of most laptops, and many desktops, are so poorly documented that you pretty much have to either guess or directly measure their specs.

Technician1002 wrote:A quick note on using soundcard mic inputs. To reduce background noise, many sound cards heavily filter the input to speech frequencies. this can filter out high speed events and round them out, so instead of getting a pop with a sharp easy to measure risetime, you get a rounded molehill waveform. Avoid the mic input on most sound cards.

Soundcards often roll off the low end of the spectrum as well. In particular, they often start to attenuate below 200Hz or so to reduce 60 and 120Hz noise that's pretty significant around a computer. In addition they of course roll off below the audio lower end of 50Hz or so.

For most samples the rise time, or it's distortion by the card, is pretty irrelevant. I would strongly suggest against using the rise time itself as any kind of an actual measurement. If you pick a consistent spot on the peaks, like the first significant data point up out'a the noise, then the rise time affects largely cancel themselves out. Both peaks have essentially the same distortion, both times are shifted by very nearly the same amount, the delta time (the only thing you really care about) is correct. At least, it's almost certainly correct within one or two data points which is the intrinsic accuracy and precision of the sound card.
Use the audacity amplify function instead. It will preserve the rise time.

Or just zoom. I don't think "amplify" does anything different than zooming if all you are trying to do is click on a point in the trace. You can zoom, or "amplify" or "normalize", they all accomplish the same thing in the context of just picking off two time points.
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Unread postAuthor: chinnerz » Mon Dec 28, 2009 8:48 am

looks good, just like something i would make.
i am kind of new to all of this but i have done some electronics at school. can you plz provide a circuit diagram?
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Unread postAuthor: jackssmirkingrevenge » Mon Dec 28, 2009 8:55 am

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Unread postAuthor: chinnerz » Mon Dec 28, 2009 9:05 am

wow, do you have those book marked? Because that was some quick work!
Also thankyou! I have decided that this will be my next project.
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Unread postAuthor: jackssmirkingrevenge » Mon Dec 28, 2009 10:27 am

chinnerz wrote:wow, do you have those book marked? Because that was some quick work!


No, I just know >>how to search effectively<<

Also thankyou! I have decided that this will be my next project.


I would make a launcher first if I were you, no use having a speedometer if you don't have a car ;)
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Unread postAuthor: chinnerz » Mon Dec 28, 2009 9:30 pm

i do have 1, it’s a bit basic (just uses a ball valve and compressed air), but it launches nails halfway into 19mm pine at 80psi . and i have always wanted to know how fast it shoots.

also thanks for the search help.... i didnt see it... now i know im going blind.
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Unread postAuthor: inonickname » Mon Dec 28, 2009 10:35 pm

I'm quite amazed at how simple this can be to setup.

I've ordered some phototransistors and 3.5mm stereo jacks to make one with. Just need to make a nice box to rig it up in.

If ambient light is insufficient what would be the best kind of (portable light source- batteries) to use? Ultrabright led's? Regular old bulbs? Et cetera.

Nice work Boyn :wink:
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