
Show HN: A high-speed laser camera trigger for under $2 - ascorbic
http://www.vela.io/posts/building-a-laser-camera-trigger-for-2-dollars/
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laxatives
Did something very similar for a final project in a physics/electronics
course.

[https://www.dropbox.com/s/ox5wxmnhzg045b4/Final.pdf](https://www.dropbox.com/s/ox5wxmnhzg045b4/Final.pdf)

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ScrewYouGuys
Nice! Hope that milk didn't end up on your cereal afterwards!

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erichocean
This post completely sums up what makes HN great.

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omegant
Find that lately there are less of this kind of Hacking articles and those
talking about interesting and inusual things, and much more about New
frameworks or libraries.

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glibgil
I went back into the archive and tried to run into a hardware hacking post
before a framework post. It went, startup, startup, Google buys YouTube,
startup, startup, then this
[https://news.ycombinator.com/item?id=1981](https://news.ycombinator.com/item?id=1981)
(2694 days ago). I couldn't find evidence that this site cut its teeth on
hardware hacking.

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omegant
It not specific on hardware, it's general about all things not about
programing and new products. Also it's not about new posts, at the new section
I keep finding them. It's that they hit the front page less frequently and
when they make it the fall to the second or third page in a mater of one hour,
compared to the framework or product posts that stay very high with relatively
less points. Maybe it's not the case, maybe it's just the habituation to HN
contents after three years of daily reading. If it happens I don't know if
it's due to the new curation team (for example now I find that conversations
are not growing so much into long rants about small details as before) or to
more people flaging non "programmer" stuff more than before.

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joe_bleau
$2 sounds really cheap--did I miss the laser on the bill of materials?

Anyone else hoping for a modern and inexpensive replacement for the legendary
classic EG&G microflash?

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sp332
_I picked up a 1 mW pointer for £1.98 on eBay._ That's about $3.38 USD.

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michaelmior
> I’m only including the cost of components, and not things like cables,
> breadboards or the laser pointer (or flash).

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oldmanjay
I like that! I'm going to start giving estimates like that

"I'll do this for free, not including my hourly or the cost of materials"

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aceperry
Gotta wonder about the schematic, looks like it's wrong. The battery and the
cathode of the opto is not connected correctly.

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kwantam
Looks correct to me. The idea is to trigger in the _absence_ of the laser---
i.e., when the beam is broken by a projectile.

When the laser shines on the base of the phototransistor, the transistor pulls
current from the node between the two resistors. Assuming the laser causes
sufficient electron-hole pair generation in the base, the transistor can pull
a bit more than 1mA (5V/4.7k) from the battery; the photodiode inside the
optocoupler then has 0V across it, and the output of the opto is high-Z (i.e.,
not conducting).

In reality, the phototransistor's collector won't pull much closer than a
couple hundred millivolts to its emitter while conducting that much current
(the transistor goes into saturation), but that's fine: most optocoupler
diodes have a forward drop of 2V or more when they're conducting sufficient
current to turn on the output.

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sigterm
I don't see how the opto can ever be turned on? Its cathode is always at
highest potential in the left half circuit.

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kwantam
Ah, I see the confusion. The power supply should be connected such that the
positive terminal is on the left. If you look at the breadboard, you can see
that this is, in fact, what's built. My description of the circuit's operation
above is accurate when the power supply is properly connected.

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bnejad
This is an awesome post, I love seeing these kind of projects. The money shot
at the end with the BB is very cool. Nice job!

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ascorbic
Thanks!

