5 ms·

Show HN: A high-speed laser camera trigger for under $2

88 points by ascorbic 12y ago

bnejad 12y ago
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!
- ascorbic 12y ago
  Thanks!
joe_bleau 12y ago
$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?
- erichocean 12y ago
  He said explicitly he's excluding it (and a few other things).
- sp332 12y ago
  I picked up a 1 mW pointer for £1.98 on eBay. That's about $3.38 USD.
  - michaelmior 12y ago
    > I’m only including the cost of components, and not things like cables, breadboards or the laser pointer (or flash).
    - oldmanjay 12y ago
      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"
- mcpherrinm 12y ago
  I'm sure I've bought laser pointers at Dollarama before (for $1 CAD) and those included batteries: Even if the total BOM is $3, it's still pretty cheap.
- ascorbic 12y ago
  A cheaper, safer replacement for the EG&G air-gap flash is exactly the final goal of my project, but it will take a few months. Expect a Kickstarter. The BOM doesn't include the laser. I'm using the laser sight on the air pistol, and I tested it with a cheap eBay laser pointer.
erichocean 12y ago
This post completely sums up what makes HN great.
- omegant 12y ago
  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.
  - glibgil 12y ago
    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.
    - omegant 12y ago
      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.
  - marincounty 12y ago
    And the Gold Rush! I like original stuff like this. Sometimes, if I feel like pulling off my head when I have to read about another App. Yes, I know this is a Programers site, so I expect to read about New Apps, and Websites, but there seems to be a plethora of Developers just looking for the next big payday? It seems like the only people getting rich are the one's who market to developer masses, or if you get lucky Mark might buy your App for 3 Billion dollars.(I still haven't recovered from that transaction. I believe they only had one vague patent?)
laxatives 12y ago
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
- aceperry 12y ago
  Nice pics!
- kator 12y ago
  Very nice write-up!
- ascorbic 12y ago
  That's really cool! Love the setup pics too.
- ScrewYouGuys 12y ago
  Nice! Hope that milk didn't end up on your cereal afterwards!
aceperry 12y ago
Gotta wonder about the schematic, looks like it's wrong. The battery and the cathode of the opto is not connected correctly.
- kwantam 12y ago
  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.
  - sigterm 12y ago
    I don't see how the opto can ever be turned on? Its cathode is always at highest potential in the left half circuit.
    - aceperry 12y ago
      Yeah, the LED in the opto isn't even connected correctly. I doubt it would ever light up. I left a post on the website explaining how it should have been setup.
    - kwantam 12y ago
      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.
  - 12y ago

88 points by ascorbic 12y ago

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!

ascorbic 12y ago
Thanks!

joe_bleau 12y ago

$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?

erichocean 12y ago
He said explicitly he's excluding it (and a few other things).
sp332 12y ago
I picked up a 1 mW pointer for £1.98 on eBay. That's about $3.38 USD.
- michaelmior 12y ago
  > I’m only including the cost of components, and not things like cables, breadboards or the laser pointer (or flash).
  - oldmanjay 12y ago
    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"
mcpherrinm 12y ago
I'm sure I've bought laser pointers at Dollarama before (for $1 CAD) and those included batteries: Even if the total BOM is $3, it's still pretty cheap.
ascorbic 12y ago
A cheaper, safer replacement for the EG&G air-gap flash is exactly the final goal of my project, but it will take a few months. Expect a Kickstarter. The BOM doesn't include the laser. I'm using the laser sight on the air pistol, and I tested it with a cheap eBay laser pointer.

erichocean 12y ago

This post completely sums up what makes HN great.

omegant 12y ago
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.
- glibgil 12y ago
  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.
  - omegant 12y ago
    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.
- marincounty 12y ago
  And the Gold Rush! I like original stuff like this. Sometimes, if I feel like pulling off my head when I have to read about another App. Yes, I know this is a Programers site, so I expect to read about New Apps, and Websites, but there seems to be a plethora of Developers just looking for the next big payday? It seems like the only people getting rich are the one's who market to developer masses, or if you get lucky Mark might buy your App for 3 Billion dollars.(I still haven't recovered from that transaction. I believe they only had one vague patent?)

laxatives 12y ago

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

aceperry 12y ago
Nice pics!
kator 12y ago
Very nice write-up!
ascorbic 12y ago
That's really cool! Love the setup pics too.
ScrewYouGuys 12y ago
Nice! Hope that milk didn't end up on your cereal afterwards!

aceperry 12y ago

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

kwantam 12y ago
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.
- sigterm 12y ago
  I don't see how the opto can ever be turned on? Its cathode is always at highest potential in the left half circuit.
  - aceperry 12y ago
    Yeah, the LED in the opto isn't even connected correctly. I doubt it would ever light up. I left a post on the website explaining how it should have been setup.
  - kwantam 12y ago
    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.
- 12y ago