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Build Your Own 10Mbit/sec Optical Data Link 145

redcliffe writes: "This website has complete plans to build a 10 megabit per second optical data link that can work over up to 1 kilometre. It uses fairly cheap components, such as standard LED's instead of laser diodes. This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it."
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Build Your Own 10Mbit/sec Optical Data Link

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  • And does it have the option of an optical 100MB switch? Or perhaps an interface to isolinear chips?
  • Why not 802.11b? (Score:4, Insightful)

    by msolnik ( 536110 ) on Saturday December 22, 2001 @01:15PM (#2741553) Homepage
    The equiptment is cheaper easier to make/get and can get further range. I can get upto 15 miles in Houston with 2 15db direction antennas that you can get for 40$ a peice.
    • by laserjet ( 170008 ) on Saturday December 22, 2001 @01:23PM (#2741578) Homepage
      You have a good point, and 802.11b probably would make sense in most conditions. The only benefits that this would offer you are 1) if you work in an area that has too much RF interference for 802.11b to work correctly, and 2) this would be more secure that 802.11b. For instance if you want to run a connection to your neighbor across the street, to intercept your connection, someone would have to get exactly in line with the transceiver, whereas 802.11b is broadcast all over the place.

      Aside from that, it just looks like they built it because they could, and that, is reason enough.

    • 802.11b only works over distance when the path isn't impeded. Buildings, mountains, etc in the way will degrade it. In general, an optical circuit has superior performance than a metallic circuit which has better performance than an RF circuit. But there are very good reasons for doing 802.11 networks. One of them is it is hard to legally lay fiber/wire when you are a hobbyist.

      Boston area people interested in free 802.11 nets should take a look at
      • "802.11b only works over distance when the path isn't impeded."

        since when does IR not need direct line of sight? or did i miss the part how light can pas thru solid buildings and is unaffected by heat waves
        • since when does IR not need direct line of sight?

          The lack of blinky light innovation of the average person amazes me. Improvise:

          Bounce it off the building down the street. Perhaps up the power and bounce it off the clouds like weather radar. Integrate your LED Christmas lights as the emmiters. Hook up the ethernet AUI connection to the flyback circuit on your television for Van Eck transmission. Complete the optical link by using the FBI's monitors in the van down the street as the optical receiver. The possibilities of bending light around the corner are endless!
          • sorry I was not think about bouncing it off things but its going to be pretty hard to aim it and get a usable connection if you are doing all that just to get a wireless connection :)
    • Why not use any existing technology? The reason is that it's a cool project to do between you and your geek friends. Anyone could go out and buy necessary hardware to do anything.. but to say you built it, it's pride you can't buy. =)
    • Hang on, you've said that your antennas cost $40 each, this brings your total to $80. This, with the added wireless cards (costing $100?) would bring the price up to at least $280.

      And as these antennas are directional, you lose one of the main advantages of radio and 802.11 - being omni-directional. Surely therefore, even though 802.11 has greater range directionally, over a shorter distance, this LED implementation might be more cost effective?

      Just wondering...

      • Well you can get the 64/40 bit WEP 802.11b Orinoco cards for $60 from places like - wait, I see some Proxim ones for $40... I haven't dealt with (got Dell OEMed Orinoco stuff before I found out about JustDeals) but the price sure sounds good.

        I agree on loosing the omnidirectional stuff but another card would solve that problem ;).
    • Yeah, for long distance 802.11 is going to be the way to go, although I am going to experiment with methods of getting more range out of it. If you only have a short distance, like to go a couple of streets away, this may be cheaper.
    • In some european country you have to ask and pay to trasmit radio signal over a public area (so also over a street and so on)... So, direct comunication like this could result in a cheaper choice.
    • 802.11b is effective in Europe, but the emission regulations mean that we can't use boosters to get the sort of range that hackers do in the US and Australia. We can't even use very high-gain antennae. So this is pretty cool. Remember also that this is only the 2nd model he has build - this could get a lot better with some time, and it is adding to the further congestion of the 2.4Ghz spectrum.
    • It's cheaper and easier where the local legislation doesn't require you to register the link, and terribly expensive where you pay per transmitter per kilohertz. Russia (And maybe .cz) is such a country.

      One of Irkutsk ISP's works with 802.11b only. The license fees are about 1000 roubles per month while the average monthly income is 3000 roubles (30 roubles are 1 US$). And the second ISP uses 802.11b covertly. (The prices may be outdated)

      There are even more strange countries. For instance, German telecoms have per-minute phone fees but legal CB data, so Germans produce 9600-baud CB modems and use the CB network.

      Also, don't forget that the 802.11 requires either the expensive access point placed somewhere on a roof or the thick and expensive cable from a roof to your computer.
  • bah (Score:2, Funny)

    by nomadic ( 141991 )
    This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it.

    Well where's the fun in that?
  • by Anonymous Coward
    you wont be able to see em from 1km away, so how would you kow where to aim the things?
  • Well, what happens if you have an infestation of pigeons around where you live? LED's aren't easy to clean if they're in a tube
  • by Anonymous Coward on Saturday December 22, 2001 @01:29PM (#2741591)
    You'll shoot your eyes out! You'll shoot your eyes out!
    • > turn dial to 1
      > shoot floyd with laser
      A red beam shoots forth from the laser and strikes Floyd. He shrieks and curls into a ball in the corner.

      > turn dial to 0.5
      > shoot floyd with laser
      A near-invisible infrared beam shoots forth from the laser and strikes Floyd in the eyes. Floyd blinks, and trundles out of the room.

      Many years later, Floyd begins to see dark floaty bits in his vision. Floyd looks confused, and trundles off to play hider-seeker.

  • by kordless ( 48957 ) on Saturday December 22, 2001 @01:30PM (#2741594)
    "This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it."

    It looks as if the author has learned this first hand if the font size on the instructions is any indication.

    Check out Grub []!
  • From the website, The operation is very reliable and immune to interference.

    um... immune to interference? So, you've got a link going to the divorcee down the block and the two of you are getting naked on-cam, and the blinds are open (of necessity) and you don't think the little crowd of neighborhood kids at your window is going to interfere?

  • Sigh... (Score:4, Informative)

    by cperciva ( 102828 ) on Saturday December 22, 2001 @01:33PM (#2741601) Homepage
    It uses fairly cheap components, such as standard LED's instead of laser diodes. This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it.

    The mere fact lasers are used in most fiber optics does not immediately render them dangerous. Typical power levels are on the order of a few mW, far too low to cause any permanent damage.
    • Re:Sigh... (Score:2, Interesting)

      by mlknowle ( 175506 )
      Exactly - the biggest saftey risk here is those nasty cuts you can give yourself with Fiber Optic tubing.

      I once had a .5mm strand of the stuff stuck in my thum - it took weeks of soaking in warm water to get it out.
      • Re:Sigh... (Score:5, Informative)

        by dattaway ( 3088 ) on Saturday December 22, 2001 @04:16PM (#2741987) Homepage Journal
        I wish this were true. Many years ago, I was fascinated by lasers; unfortunately, infrared isn't too visible. Several years later, I now have dark stuff floating around in my eyes. For a person 33 years of age, I would not recommend looking at concentrated sources of energy, no matter how small.

        It may be a milliwatt, but its still heat: focused smaller than the head of a pin. It may burn. Damage in the eyes shows up many years later.
        • by Anonymous Coward
          i have one too and asked the eye doctor about it, he said it's normal and doesn't have to do with laser irradiation - it's a warp in the transparent body of the eye. and i'm younger than you.
        • Floaters are normal. Well if your retina could be flacking off but seeing floaters isn't so surprising in a 33 yo. or 25 yo. for that matter.

          But even those LED's they are using will hurt your eyes if you stare at them for a few minutes. IR is nasty, it dries your contacts while looking like a not so bright red LED...
    • Re:Sigh... (Score:1, Insightful)

      by Anonymous Coward
      Having said that, those few mW are very consentrated compared to say 70W lightbulb.
    • power/area on the retina is what matters.

      Laser systems can be beamshaped to provide much
      higher power densities than incoherent thermal sources.
    • first off. i wouldn't consider a LED any less dangerous than a laser. yes, a laser will generally generate a higher powered and more focused beam, but the "dangerous" lasers used in telecomm very often will not exceed 5 to 10dBm.

      5mW = 6.99dBm. i wouldn't trust looking at anything with +dbm fairly concentrated source... would you?

      on that note, there's lots of info on laser safety at google []

      a nice pretty chart [] courtesy of waterloo pointing out what's at risk: your retina, your colour vision, night vision, and skin burns. it's skin burns that are unlikely at such low levels, not eye dammage.

      here's an abstract from a ubc page: []
      "Laser light in the visible to near infrared spectrum (i.e., 400 - 1400 nm) can cause damage to the retina resulting in scotoma (blind spot in the fovea). This wave band is also know as the "retinal hazard region"."

      i had a co-worker that used to tell me not to worry about the 1500nm range, as "it's only the 1310nm range that you have to be worried about, sheesh." i was nutorious for turning off the laser every time was changing connections.

      i probably had a over a mil worth of devices and test equipment on my bench. had a nice automated test (LabView) running. 5dBm Tx laser (MZ pumped up to 10gig internal modulation - yeah baby!), a few km (miles, whatever) of fiber, variable attenuator (VOA), and a nice 10gig Rx (APD).

      so anyways, the freeking comm cables (HPIB) controlling the VOA went skitzoid or something. the VOA reset to ZERO attenuation. only a few seconds later, and the APD was fried. (currents jumped from low double/tripple digits to four digits. in mA. so yes, that's amps.)

      my stomach sank as i saw the bit error rate (on the BERT) go to 100%. several grand. poof. gone... just like that.

      i got the idea pretty quick that even components designed to handle that stuff get very cranky very quickly. let alone your eyes. you've only got 1 chance with 'em... don't muck it up.

      - from then on in my very short distance tests had a 12dB fixed optical attenuator (less than $20?) instead of relying on a VOA (probably a few grand).
      - oh... and i stuck to what i was supposed to be testing: over a few hundred km instead of a few km. heh heh hah... oops.

      • From Health Canada []:
        But at levels between 1 and 5 mW, so much light rushes into the eye that it suffers a temporary condition called flashblindness. It is similar to the effect that occurs during flash photography where the image of the flash source remains in the eyes for a few seconds and then fades away. There is no long-term effect from flashblindness.

        It may not be particularly pleasant to have one of these lasers hit you in the eye, but it won't do any permanent damage.
        • Neat.. Health Canada actually has something useful. and... I somehow feel like I'm in a session of parliament, because you should probably quote more of the Health Canada page [] you linked to:

          The power of light emitted by these battery-operated lasers used to be less than one milliwatt (Class 2 lasers). But now the power has increased to between 1 and 5 mW (Class 3a laser) to obtain a brighter beam. Unfortunately, it also makes the laser more dangerous to the eye.

          Below 1 mW, even in the worst case situation at night, the eye directly exposed to the laser light has time to activate the blink reflex, approximately 0.25 seconds, before injury occurs. But at levels between 1 and 5 mW, so much light rushes into the eye that it suffers a temporary condition called flashblindness. It is similar to the effect that occurs during flash photography where the image of the flash source remains in the eyes for a few seconds and then fades away.

          There is no long-term effect from flashblindness. Normal vision usually recovers after a few seconds. But if one forces oneself to look directly into the beam, then permanent blindness might occur depending on exposure duration. This would be equivalent to looking directly at the sun for a few seconds.

          One thing I did forget about is the blinking part. Since 650nm is actually red [], the physiological response is to blink. This is one of the reasons class 4 lasers so dangerous: you may be looking directly into the beam and not blink until pain is induced, but by that time it's likely too late and dammage has been done.

          There's no doubt that at the Rx end significant attenuation will have occured and it will be harmless. But it's not exactly bright (bad pun) to be looking at the Tx end close-up for more than a second or so. After all, we're talking about 5mW here. []

        • This reminds me of an idiot mother who gave their young child a 5 mW laser pointer to play with.

          I was in a restaurant, and got a blast of red light in the eye. I noticed a child playing with a bright laser pointer. I wagged my finger at him for shining it in my eyes, and went on eating dinner. Later, I looked over, and much to my horror the mother had left the table and the kid was shining the pointer directly into his little brother's eye, who took it as a test of manhood not to look away. Having more balls than brains, I took it away from him and returned it to his mother (who returned 15 minutes later - she was on the payphone across the street) with a suggestion that she not allow the child to play with such a non-toy. She wasn't happy that I intervened (and threatened to call the cops), but I mentioned that walking away from two sub-4 year olds at a restaurant (knives on the table, dangerous toy, etc) wasn't exactly something that she'd want me to mention to social services.

  • This is absolutely great! A primo example that goes back to the roots of Slashdot.

    Excellent link, great article.

    Now where's my soldering gun?

  • by shoppa ( 464619 ) on Saturday December 22, 2001 @01:58PM (#2741660)
    i.e. you won't burn your eyes out if you accidently look into it.

    Reminds me of my favorite warning sticker:

    Warning: Do not look directly into laser with remaining good eye
    Despite how effective the sticker was at reminding us to keep our goggles on, the safety people made us take it down.
    • Here's a true story.

      A professor a a university in England (I think it was Cambridge) somehow accidentally looked directly into an extremely powerful laser that just happened to be in one of the labs. The laser struck him in the eye, blinding him instantly. That wasn't the nasty part, though.

      No, just when you were wondering how it could be any worse, the laser somehow reflected back from his eye and struck him in the other eye, blinding him in that eye too.

      Sounds like one of those anecdotes your Physics teacher used to make up so that you'd be extra careful around lasers, but there you have it. Physics teachers are always the best when it comes to making up anecdotes... ;)

  • As with everything in life, my time is often worth money. So who wants to be the first to tinker around and start churning these out?
    • Then you should be hawking your second hand hardware on eBay rather than hanging out on Slashdot. Years ago, stories like this were far more common on Slashdot, this is "News for Nerds, Stuff that Matters".

      It's not about marketing it, selling it, etc. It's about doing it yourself.

  • Laser? (Score:3, Informative)

    by mindstrm ( 20013 ) on Saturday December 22, 2001 @02:13PM (#2741702)
    The article quite clearly states that for 10M, they use a laser diode...
  • Hmm (Score:3, Funny)

    by Chazmati ( 214538 ) on Saturday December 22, 2001 @02:16PM (#2741712)
    From the "Making the electronics" section (emphasis mine, of course):

    Solder remaining parts into the transmitter. Put the three 74HC04's in stack (like they are fucking), and solder pins of equal numbers together. The schematic follows.

  • Got AUI? (Score:5, Informative)

    by Uller-RM ( 65231 ) on Saturday December 22, 2001 @02:26PM (#2741739) Homepage
    Has anyone else bothered to read this enough to notice that it will not work with twisted pair Ethernet? It requires an AUI connection. They even say in the FAQ, redesigning it to work with TP would be a pain in the arse.

    In order to use the circuit, you have to either buy an AUI->TP transciever, or set up a bridging machine.

    Just saving a bit of time for some people who are no doubt running out to Ripoff Shack grabbing l33t bl00 leds.
    • Re:Got AUI? (Score:2, Informative)

      by neonstz ( 79215 )
      Well, getting used NICs with AUI should be a problem I think. I've bought quite a few at large garage sales. If it is a problem getting one however, just get a Sun Sparcstation 5 or some other machine with built-in AUI. :)
    • Re:Got AUI? (Score:2, Informative)

      by Zog ( 12506 )
      It's not the end of the world. AUI adapters are easy to find and are pretty cheap (mine was ~$10 from a store that sells random computer cables/adaptors; they can be had online for about the same).

      Also, using AUI makes a fair amount of sense - it *is* simpler, so you don't have to worry about the signals as much, so it's easier to make at home :)

      Now, compare the price of parts plus the AUI adapter (I'll let you do that one) to the price of a cheap (though crazy fast) commercial link, and it should make sense why this is good. Also, as someone else already stated, there's the simple fact that you're using your very own homemade optical datalink ;)
    • Huh? A LOT of older ethernet network cards have AUI connectors. You don't see them on the 100mbps cards but since this maxes out at 10mbps anyways, who cares? If you're going to spend the time building this device, getting ahold of a compatible network card is not the biggest obstacle. :)


      Play with my webcams and turn my lights on/off at []
  • by Animats ( 122034 ) on Saturday December 22, 2001 @02:34PM (#2741761) Homepage
    This works because the AUI interface is still around. That's the original, really simple, interface used with the original Xerox PARC Ethernet tranceivers in the 1970s. It still works.

    Others have done similar things with the AUI interface. Here's an RF link [] using the same technology.

    If you want more range from the optical link, I'd suggest putting an optical interference filter (from Edmund Scientific) in front of the receiver. Pick one that matches the color of the transmitted beam, and you'll reject most other light.

  • by Brian Stretch ( 5304 ) on Saturday December 22, 2001 @02:45PM (#2741786)
    These, or higher-speed commercial point-to-point transmitters, seem like a neat way to set up a wireless backbone for a (community) wireless network. Then you just hang WiFi transmitters off the backbone access points. Actually, I'd want something a bit faster than 10Mbps for a backbone (aggregate multiple transmitters?), but you get the idea. I'm not sure it'd be superior to using the new 802.11a 5GHz gear for such a backbone, but in either case, you avoid dealing with the local telco monopoly, which is always a Good Thing.

    Maybe put small caching proxy servers at the access points backed up by a big one at the end of the network? Or just the latter. If you're liable to wind up with a Linux box at the access points anyhow...

    I've already got a cable modem and I'm lazy, so I'll let someone else run with this :-).
  • For real, who has seen/done this? The opportunities for creative mayhem seem mindboggling. Start on Saturday morn, open ur wholesale catalog and take a walk to the neighborhood hardware store....Monday coming around like the wheel has just been re-invented.

    This rox, liono.
  • by Alien54 ( 180860 ) on Saturday December 22, 2001 @03:05PM (#2741832) Journal
    There was this old story [] about a company doing something similar with lasers between skyscapers, etc. I suppose the usual fog and bird problems apply. And maybe some mean spirited neighborhood kids with a couple of balloons

    Personally, I wouldn't mind a way to do this sort of thing by shortwave. It would be great for WAN applications between cities [shrug]

    • Yeah, and somebody did actually mention Ronja in the comments back then.
    • In addition to AirFiber, there's also Terabeam doing building-to-building optical technology. They're in the 100Mbps - 1Gbps speed ranges, with distances of 1km if you don't have fog, or 500 meters if you get fog (they're based in Seattle, so they've had plenty of weather to get real experience with :-) I think there are also a variety of other equipment makers.
    • Is that this is just _now_ getting posted, about Ronja, that is.

      If you look through the comments of that "old /. story" you posted (sort the thing "Oldest First", the comment will be on the first page toward the bottom), you will see a comment in there I made in which I included the following link:

      My comment's title was "Homebrew it!" - I noted that Ronja seems to be the best - instead of lasers, ultra-high brightness LED's are used - no great distances here, but aiming doesn't have to be as accurate, fog/rain/birds are less of a problem, the hardware interface is rather simple, and the LED's (and other parts) are cheap!

      Makes me wonder what took this so long to be noticed...
      • Never saw that one. You should have submitted it as a story.....
        • Probably should have - I probably didn't because many of the stories I have submitted in the past (with the exception of a few "Ask Slashdots") have been turned down (only to "of course" appear later).

          Anyhow, it may have not stood out in my post because I got lazy and didn't set the links up properly - just bleched them on the page...
    • My school uses a 10Mb line-of-sight microwave system that covers about 3-4 blocks, between the main building and an annex; living int the rainy Pacific Nortwest, if rain caused it problems we would know.

      IIRC, Ma Bell used to use microwave connections for long-distance lines
  • Dr Evil (Score:1, Redundant)

    by sporty ( 27564 )
    Alas, poor mini-me will have nothing to hump. (/austin powers 2 reference)
  • ****Caution - do not look into laser with remaining eye!****
  • Eye burn? (Score:4, Informative)

    by rew ( 6140 ) <> on Saturday December 22, 2001 @04:09PM (#2741971) Homepage
    This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it."

    Ehmm. Modern High efficiency LEDs also carry the "don't look directly into this" warnings. And those things are BRIGHT.

  • I live in Vancouver, and wintertime reduces the range of these devices to much less than 1 KM. Much of the time when it's raining, visibility isn't that great, and these things require telescopic lenses to get even 1KM range.

    I would have to wonder whether this would be much more effective indoors however. It's much more secure (to block packet sniffers, simply close the curtains) than wireless would be, if only you could make the device small enough to put a little blinkenlight in your ceiling that would relay packets around. (in the ceiling because you don't want your cat getting in the way of your data transfers...) It might be a neat project. :)
    • For transmitting this data inside a room, I'd suggest using infrared LEDs. Not only could the data be bounced off walls (which would eliminate a lot of the bulky shrouds and lenses), but also you wouldn't have an eerie orange glow above your head (and perhaps prevent your cat from getting an epileptic fit).

  • This sounds a wonderful project to try ... I always wanted to get into actually building things (rather than building virtual things / using premade parts that just "plug") ...

    What this page is missing is an approximate on how much I will have to spend, all things considered. There's a nifty listing for the parts and some pointers on what lenses may cost, but no total or any indication what price-regions we are talking about.

    So, could any of the more technically inclined people here give a reasonable estimate on whether to spend $50, $200, or $1000 for one working link ? Thanks in advance ...
  • by new500 ( 128819 ) on Saturday December 22, 2001 @07:48PM (#2742444) Journal

    . .

    Hey, flame / mod me away here - I deserve it because I've been looking for a thread in which to post this rejected story sub from a week ago . . But what the heck here it is anyway :

    ( I was originally going to say this post is well OT because of the distance limitations of the below, but what about using this transmission in a PA system at a stadium, or a train station, where volumes and hence transmission possibilities are greater / farther? And just how much is over the air networking really explored by companies? This story is already dang good and right where it hurts for community and campus networks, but if I were building this kit for business I'd be thinking that planning permission would be the area I'd be researching most. In other words, do the "amateurs" have a real chance at a lead in this technology, especially price / performance wise? After all, you and I personally *don't* have to make budgets for contingent liability just in case the town planning dept. gets difficult. I'm all for guerilla networks - take a look at the below . . )

    Aerial Acoustic Communications

    Network with just a pair of pc speakers and a $5 mic! This recent paper [] explains the theory and writes up the experiment.

    This may not be the answer to all your needs - 1000bps was one of the best results - but the authors talk about short distance communications for PDAs, or a television using sound for remote control. The environmental noise against which the authors deployed Spread Spectrum techniques, and a reference to audio steganography make for interesting reading, and radio hams may appreciate the use of FSK. Is this the future, or just a hint that playing albums backwards wasn't really the way to get the message?

    There's also a lecture video here [] which was held at PARC on 11/8/01. You can grab the stream as a file using ASF Recorder [] or you can read up on some applications musings here []. Happy Listening . .


  • This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it."

    This is just like the sad story of napster etc

    Company: No, it's completely legal because you can use it for networking, which isn't at all illegal.

    Feds: Okay then, implement some filters or something to stop people using it as a weapon

    Company: But we'll lose all our customers!

  • ... 10 megabit per second optical data link that can work over up to 1 kilometre.

    Does this data link retain it's speed of 10mb/sec even when you get further out towards a kilometer? I'm sure that you probably lose some packets along the way, kind of like CAT5.
    • Re:One kilometre. (Score:3, Informative)

      by redcliffe ( 466773 )
      AFAIK, it either works or it doesn't. Like you get 10mb/sec or you get nothing. There is no link quality control on it from what I can see.
    • Data speed is not like the speed that you get in a car. Basically the link is based on the wavelength of the data. So over distance, wavelength does not change.
  • This harks back to the days of strings and tin cans from a long time ago where kids would run the string to their next door neighbors. Well, now kids will be making 10mbs wireless connection and instant messaging, video conferencing, or fragging each other in Quake...this is the Advancement in Technology in comparison...
  • This is a interesting funny project to buid your 2 computer network using 2 laser toys. laser.htm []
  • This also makes it a lot safer to work with, i.e. you won't burn your eyes out if you accidently look into it."

    The site says the EIRP is 10kW -- you will most certainly be hurt if you stare into this thing!

  • From the "Fundamentals of Manufacturing Operations" section:

    When cutting tin with tin cutters, take care not to cut off your finger.

    Seems like good advice.

Honesty is for the most part less profitable than dishonesty. -- Plato