Gotta wonder about the schematic, looks like it's wrong. The battery and the cathode of the opto is not connected correctly.
Show HN: A high-speed laser camera trigger for under $2
11–20 of 29 posts
Re: Show HN: A high-speed laser camera trigger for under $2
#12Gotta wonder about the schematic, looks like it's wrong. The battery and the cathode of the opto is not connected correctly.
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.
Re: Show HN: A high-speed laser camera trigger for under $2
#13$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?
I picked up a 1 mW pointer for £1.98 on eBay. That's about $3.38 USD.
> I’m only including the cost of components, and not things like cables, breadboards or the laser pointer (or flash).
Re: Show HN: A high-speed laser camera trigger for under $2
#14This post completely sums up what makes HN great.
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.
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 (2694 days ago). I couldn't find evidence that this site cut its teeth on hardware hacking.
Re: Show HN: A high-speed laser camera trigger for under $2
#15This post completely sums up what makes HN great.
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.
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?)
Re: Show HN: A high-speed laser camera trigger for under $2
#16Did something very similar for a final project in a physics/electronics course. https://www.dropbox.com/s/ox5wxmnhzg045b4/Final.pdf
Very nice write-up!
Re: Show HN: A high-speed laser camera trigger for under $2
#17Gotta wonder about the schematic, looks like it's wrong. The battery and the cathode of the opto is not connected correctly.
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 insi…
I don't see how the opto can ever be turned on? Its cathode is always at highest potential in the left half circuit.
Re: Show HN: A high-speed laser camera trigger for under $2
#18Earlier quoted context omitted.
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 insi…
I don't see how the opto can ever be turned on? Its cathode is always at highest potential in the left half circuit.
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.
Re: Show HN: A high-speed laser camera trigger for under $2
#19Earlier quoted context omitted.
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 insi…
I don't see how the opto can ever be turned on? Its cathode is always at highest potential in the left half circuit.
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.
Re: Show HN: A high-speed laser camera trigger for under $2
#20Gotta wonder about the schematic, looks like it's wrong. The battery and the cathode of the opto is not connected correctly.
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 insi…
>the transistor pulls current from the node between the two resistors
The battery is connected incorrectly for this scenario to work. Node 2 of R2 should be connected to the positive battery terminal for correct flow to the LED.
>the phototransistor's collector won't pull much closer than a couple hundred millivolts to its emitter while conducting that much current
The transistor won't operate like that given the way it is biased in the circuit.
>most optocoupler diodes have a forward drop of 2V or more
The data sheet for this opto lists the forward voltage drop as 1.3 - 1.7 volts.