Hackaday Links: November 4, 2012

Wait, you’re using a Dremel to cut PCBs?

Cutting copper-clad board or – horrors – depanelizing PCBs is a pain if you don’t have the right tool. Over at Hub City Labs they’re using a small, cheap metal shear & break. Bonus: it can cut and bend sheet metal, so the Hub City folks can also make enclosures.

Color Codes? Yes, Color Codes.

[Joe] sent in a cool utility he whipped up called resisto.rs. Plug in a resistor value, and it’ll spit out the 4-band, 5-band, and surface mount labels for that resistor value. Pretty neat.

Parallel Ports

Parallel ports may be a dying breed, but that didn’t stop [Electroalek] from putting together a VU meter that connects to his LPT port. It’s an extremely simple design; just connect some LEDs and resistors to the pins of a parallel port, and you can easily control them via software on a computer. Playing around with an LPT port used to be common knowledge, so we’re glad to see [Electroalek]’s work here.

The power is out, but Radio Shack is still open

[Jason] is stuck in New Jersey without power and needed a way to charge his phone. He whipped up a cell phone charger using an RC car battery and an LM317 voltage regulator. It’s an easy circuit to piece together, and judging from [Jason]’s picture will hopefully keep his cell phone charged until the power comes back on.

Shooting 50 Nerf darts all at once

If [Rob]’s project log is to be believed, it looks like they’re having a lot of fun over in the Sparkfun warehouse. They decided to have a full-scale Nerf gun war for a summer intern’s last day. [Rob] came up with a DIY Nerf shotgun that shoots 50 darts across the room, just waiting to be found sometime in the next decade.

There’s a great video of [Rob] firing the single barrel (yeah, they made a trident-shaped one as well) gun at well prepared but unsuspecting coworkers. Be sure to check out the comments of this post to see Hackaday readers frothing at the mouth because PVC pipe isn’t a pressure vessel guys. You’ll all surely die.

43 thoughts on “Hackaday Links: November 4, 2012

    1. I just have a pair of medium sized metal shears that are good for almost all fiberglass/pcb cutting needs, perhaps the only exception being when I need precision cuts — for that a small table saw serves well.

      Using dremel for cutting PCB is a very bad idea because you don’t want to breathe the tiny glass/epoxy particles that fill the air when you’re doing so.

  1. Does any software exist that can take a photo of a resistor and then tell me the values? Because of my colorblindness I am incapable of learning to interpret resistor bands.

    While it’s powerfully educational to have my four-year-old daughter telling me resistor colors, now that she’s mastered it I’d like a utility that can do it for me and also tell me the specs.

    1. I am not color blind, but I have issues with that too so I tried finding a way to differentiate the color bands from images, but I never got it working for the different possible lighting conditions since the range from Brown to Yellow where all being mistaken for their adjacents. I’ll give it another go in a few months, but the best solution I found was an autoadjust ohm meter left on.

  2. The Enco Model #130-5710 is what I use to cut my SeeedStudio boards. I bought it about 8 years ago and it is still going strong. The current web price is $55. At 40lbs, it is quite heavy, so look around for the Enco free shipping code. I think this month’s free shipping code is NCCOCT, but I could be wrong. I did build a little platform hold the PCB while I cut it. I have no relationship with Enco other than being satisfied with this particular product (that I use exclusively for cuting PCB’s.)

  3. Great, now Brian is mocking us for being concerned when someone makes an unsafe device by pressurizing PVC pipe.

    It’s a stupidly dangerous thing to do. People tend to keep doing it in projects. These projects keep ending up as features on Hackaday.

    Until one of those three things changes, we the community will continue to warn people that pressurizing standard PVC pipe is dangerous.

    Your sarcasm regarding this serious matter is neither helpful nor appreciated Brian.

    1. Show me one PVC air cannon that has exploded and caused injury to the operator.

      I mean, I’ve posted a story about a 2000 pound, rideable, hydraulic spider. Named Stampy. That’s an *extremely* dangerous build, if someone doesn’t know what they’re doing. Liquid fuel rocket engines? Sure, they’ll take an eye (and an arm, and a head) out.

      But no. What’s the one build that HaD commentors latch on and say is super dangerous? Nerf guns.

      I’m not saying they’re inherently safe. I just can’t believe that out of all the projects on HaD, a PVC nerf gun is the most dangerous.

      1. They aren’t the most dangerous projects, but quite easy, so the chance that someone does something without thinking is much higher (kids/teens/…). You can’t really build giant robots or advanced rockets without collection iformation and learning about the risks and how to manage them.
        For easy projects, they are not as obvious. If people decide to take that risk and do so outside of crowds, fine, but that should be an educated decision.
        I don’t know about overpressure damages, but I remember a few reports about spud guns gone horribly wrong, and I can imagine similar things that might happen with air pressure.

      2. Thank you for using the obvious argument. I have made many and seen afew go. All the ones that broke were destined to fail or were fail tested on purpose. Nobody hurt, nothing spectacular.

        Here is a fun physics thought experiment: If you can shoot a 30 gram weight at 100 m/s out of a tube that weighs 2kg, how much kinetic energy will it impose on an operator if it failed?

        using the inverse square rule and taking geometry into account the delivered kinetic energy drops from 66 to around 15 joules, or the equivalent of 1-2 paintballs hitting you.

        A thrown snowball has more chance to cause physcial damage than an air pressurized pvc pipe that fails.

      3. Brian, if this guy wasn’t wearing a motorcycle helmet, he probably would have needed to go to the hospital. http://www.youtube.com/watch?v=AQo81nqx-W8

        PVC air guns aren’t the most dangerous things featured on HaD, but that’s not the point. Doing an air-cannon with safe materials isn’t much more expensive and essentially eliminates a catastrophic failure mode.

        Air-cannons are also in the very easy first build category, and aren’t in the same league as as hydraulic rides and liquid-fueled rockets.

        It’s like making candy rocket motors. There is a relatively safe way of doing it, and many very unsafe ways. You might do it in an unsafe fashion because you never got bitten, but you should feel obligated to tell others how to do it in the safest way possible because you don’t want them getting hurt while enjoying your hobby.

        Really, this is very basic stuff like “don’t start an RC plane engine with your fingers.”

      4. Anecdotal, but a friend of mine nearly lost an eye from a pvc based potato gun (not compressed air, but still pressure failure of pvc) when it failed catastrophically and a piece of shrapnel hit him in the face, he was about half an inch low of getting serious lasting damage.

        The problem with PVC isn’t just that it fails under pressure, the problem is HOW it fails. It shatters into rather sharp pieces.

      5. Since you asked, a piano student at the university in my town blew two of the fingers off of his right hand with a PVC spud cannon. See here.

        Granted, he was using black powder and not compressed air, but pressure is pressure. Maybe the “don’t try this at home” disclaimer could be a bit less snarky?

      6. There needs to be something pointed out here that is VERY important. As signednpoole has pointed out, PVC pipe IS pressure rated, it’s printed ON THE PIPE! ABS pipe is generally not pressure rated, and that fact is printed right on the pipe as well. PVC in sizes used for potable water in household plumbing is rated to AT LEAST 100 psi (higher IIRC) to withstand normal municipal water pressure (40 – 80 PSI).

        Now, non-compressed air potato style cannon use various propelents with UNKNOWN and in many cases IMPOSSIBLE TO PREDICT (aquanet anyone?) combustion pressures. This cannot be accounted for with ANY material choice. THIS IS THE DANGER! Compressed air can be controlled and kept within the spec of the pipe. Combustion pressure from unmetered propellants cannot be controlled and is unsafe and can result in catastrophic failure of any pressure vessel (including barrels/beeches designed for firing large projectiles, see comment about blackpowder potato cannon…..)

        It stands to reason as well that firing objects the size of potatoes should already dictate that the project be undertaken by an individual capable of understanding the risks and running the build and operation of the device responsibly.

        Instead of whining about how unsafe something is why not point out resources about why it is unsafe and how to do it safely? That way those that want to replicate the project and stand a better chance of keeping fingers, eyes, and their life can learn WHY the original build was unsafe instead of being needlessly afraid. There is far too much crying foul from those who have not done these things first hand or even taken the time to read the article!

        If its not safe, then for chrisakes teach us the safe way to do it or point us to someone who can. If you can’t do that, find someplace else to troll.

    2. so how do you make it more safe really?
      will duck tape the thing help prevent the sharp pieces from flying?
      is it possible to add a safety pressure release valve of a short to the build?

      constructive criticism is always welcomed :)

  4. Wrong, I profoundly appreciate it.

    And calling this “stupidly dangerous” is disrespectful to everyone who’s done this carefully and successfully.

    Also, see ASTM D1785. PVC is, in fact, pressure rated. Some schedules of pipe to thousands of psi for the transport of pressurized liquids. And the fittings and glues manufactured for PVC pipe have to maintain the pressure rating of the system when properly applied. Jerkface.

    I was around during this build, there was a lot of care taken to ensure that the schedule of pipe used was being stressed well below spec and we were all very nervous and careful near the pressurized device.

    Sometimes, informed confidence can be mistaken for a lack of respect for a dangerous situation. People have fun doing dangerous things, though, and so long as they understand the risks and work to mitigate those risks, then they can continue to have fun doing/building dangerous things for a very long time.

    Anyone who attempts this build and hurts themselves in the process was bound to hurt themselves doing something. I like to think that the hacking community is a risk-neutral community that understands that in using tools and materials in unexpected ways we take a risk but learn something in return.

    The subtext of this entire website is “This is the wrong way to do it, if you do it this way you could get hurt, look how cool it was though.” and I resent the idea that I could be denied access to projects like these because an editor or publisher deems it too “stupidly dangerous” for the lowest-common-denominator.

    1. I’m going to respectfully ask you to refrain from this type of rant until you learn the difference between “pressurized” and “compressed.” Failures involving pressurized liquids are nothing like failure involving compressible gases. And failures of a brittle substance are different from failures of a ductile substance.

      1. Could you please explain the technical difference between a pressurized liquefied gas and a compressed gas (provided that the pressurized liquefied gas is a gas at room temp, such as nitrogen, or perhaps both the “compressed gas” and “pressurized liquid” are at an elevated temperature, such as water above it’s boiling point?) The point? Compressed gas pressurizes it’s own container, liquefied compounds will pressurize their container when at a temperature high enough to produce a vapor pressure and above.

        Liquids (more specifically all chemical compounds that are liquid under temperatures of interest, such as hydraulic fluid, CANNOT be pressurized or compressed. They can be stored in a pressurized vessel where the pressurizing force comes from compressed gas, mechanical, gravitational, or other means. There is NO reason to believe that the sudden release of energy from a pressurizing force capable of delivering equivalent action is any less dangerous that the release of energy from a “compressed gas”.

        For the sake of this argument, all materials can be considered brittle when subjected to loads far in excess of their yield strength. Steel, although ductile, will shatter like PVC when its limit is exceeded in similar circumstances (see Hand Grenade). ABS is more ductile than PVC but is certainly not a better choice. Glass tubing embedded in a several ton block of concrete would be brittle but would likely not fail from pressure in this situation.

        I’m going to respectfully ask you to refrain from making statements until you can create logical cohesive arguments that you have put some thought into and back them up with specific circumstances that validate your point, or make your misunderstanding clear enough so that we can help clarify the facts of the matter.

      2. While I provisionally agree that there can be a difference between pressurized liquid failures and compressed gas failures, I’ll ask you to remember that failure mechanics kick in *above* the material’s elastic limit.. not at 20% of it.

        I’m also at a loss to understand your reference to brittle/ductile failure in regard to PVC.. as a plastic, you could argue it either way. Personally, I’d lean heavily toward ‘ductile’ since I know something about fracture mechanics, and would expect the material ahead of a sharp-pointed crack to compress — distributing force through a large volume of material and thus lowering the amount of force available near the tip of the crack that could exceed the material’s elastic limit — rather than providing a hard fulcrum that concentrates force in a small volume of space near the crack’s tip.

        I’ll also ask you to limit your failure scenarios to those which are limited by the total amount of energy in the system, rather than handwaving in an assumption of infinite pressure supply.

        He has a pressure tank maybe 2′ long charged to 60psi (in pipe probably rated for 300psi). As soon as he opens the valve, the pressure can only decrease. The most likely failure scenario is development a longitudinal crack in the pressure chamber while he’s charging it (hoop stresses are twice as large as longitudinal stresses, so it will split the same way a hot dog does).

        Contrary to your apparent assumptions, PVC does not shatter like glass in that scenario. The crack lengthens, gas escapes through it, and the pressure in the chamber falls. The only remaining question is whether energy can enter the system from the compressor faster than it can escape from the system through the lengthening crack.

        Total energy matters though. If a 1mm cube at 1000psi fails, it goes ‘pop’. If a 10m cube at 50psi fails, it can kill someone.

      3. @ Harry
        I’m curious why you bring up steam and liquid nitrogen. You’re not going to compress nitrogen into a liquid at room temperatures. As for steam. PVC/ABS pressure ratings are for compressed liquids, not gasses compressed into liquids under pressure. They’re meant for transporting domestic water, or pressurized transfer of liquids in a factory. Things that are liquid at room temperature. The pressure ratings also are rated at a specific temperature so if you’re transporting steam in PVC pipe you’re probably above it’s pressure temperature rating anyways.

        In a 50cubic inch pipe you can only fit 50 cubic inches of water/incompressible fluid. While you can fit how ever much gas into it as you have pressure to force it in with. There are more than a few videos of destructive testing of PVC filled with compressed air.

        The whole reason the nerf dats, AA cells, Potatos, &c get launched is because pressure and volume are proportional to energy.
        If I can launch a hand full of nerf darts 50ft across a warehouse or a potato through plywood why is it so hard for people to grasp that that energy could also go into launching bits of the pressure vessle into your face?

      4. Oh, condescension… Nice… I guess anyone could’ve made that mistake, quoting the ASTM and all: “This specification covers poly(vinyl chloride) (PVC) plastic pipe, schedules 40, 80, and 120 for use with the distribution of pressurized liquids only.”

        The difference, I suppose, being that water cannot be compressed, but is transported under pressure. Pressure for which the pipe is rated.

        I swear, man, I’m not trying to be a jerk. Troll on elsewhere.

      5. Thank you macegr for pointing this out.

        To elaborate:
        The energy stored in pressurized matter is the product integral of pressure with respect to volume change.

        This means that for an incompressable liquid there is NO energy stored. Nada. No matter how much pressure it is under. For a compressable gas…

        As for failure modes, I can tell you that large fireworks launched from tubes require metal or ABS. PVC need not apply. This is entirely because the failure mode is less likely to kill the technician launching the thing.

        If you know the risk, go for it. But people new to the hobby DON’T know the risk. I was what, 15 when I built my first spud gun? Certainly didn’t know the difference between ABS and PVC.

    2. While I agree there are too many chicken littles running around everytime a PVC air launcher makes it on the site. I have to side with macegr on this one. There’s a reason the ASTM is for -Liquids-. Most of the pipe even says ‘not for compressed air’ or something to that affect.

      That said: We get it PVC isn’t good for compressed air guns. The fact that there’s an arguement in the comments everytime one is posted means the readership realizes this. We can stop harping on it everytime one comes up. Like another poster said, this is a hacking site. The projects posted are going to be using things in ways the designer never intended them to be used -that’s the point- !

      1. Thank you for stating, the Liquids rating. It drives me nuts, when people say its pressure rated. It matters what TYPE of rating! My reason for the safety factor, comes from school. If you couldn’t work safe, you couldn’t work period.

  5. I’m not sure it is good practice for an editor to belittle the readers. This is sure to turn off many active readers and will probably cause the readers that didn’t quit visiting this site in disgust to think for several seconds before offering their opinion/insight/tips/kudos/etc.

    1. I forgot to mention: It also will find you a pair of resistors that has the value you want. E.g. If you need a 5K Ohm resistor, it will find that a 7500 Ohm and a 15000 Ohm resistor, connected in parallel are exactly that resistance. Then you can click on the values and it will show you want that resistor looks like.

      And… you can bookmark it on your smartphone, and it will be instantly available, even when you don’t have a data connection, because it has a manifest to stay in the cache. So it’s an app, as well as a web page.

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