Laser Cutter Exhaust Interlock Is Silly, Educational, Useful

If there’s one maker space that has an excess of mad scientist type hackers, it has to be LVL1 in Louisville, KY. They sure do a lot of crazy stuff, like this simple device to defeat the laser cutter smoke monster. Nobody got the memo about the “simple” part. Instead they created a functional, educational and aesthetically pleasing element for the hackerspace.

LVL1 has a large format laser cutter. Laser cutters emit nasty smoke. Said smoke needs to be vented outside. To do so, it needs to pass through a scrubber/filter so the neighbouring Pigs don’t complain. So they installed a larger, better filter. The Pigs are happy, until the filter gets clogged and the smoke monster decides to escape. Next they install a pressure switch which disables the laser when the filter gets clogged. Laser cutters have a myriad of safety interlocks, so quite often, it isn’t apparent which one caused it to trip. Hence, the Laser Cutter Enable Module – LCEM.

The simple part was to install an indicator that lights up when the pressure switch is enabled, and off when not. But when it’s off, it isn’t clear if the pressure switch is off, or the indicator has failed. Simple, just install a bi-color LED – Red for off, Green for On. But then what about color blind folks who cannot tell the two colors apart? So, finally, two LED’s with clearly labelled text marking them as Enabled and Disabled.

A simple (this time for real) circuit was finally agreed upon. The SPDT contacts of the pressure switch drive the LED in an optoisolator. Its output drives a DPDT relay via a transistor. One set of contacts light up the two indicator LED’s and the other set of contacts goes to the laser cutter enable contacts. Of course, the optoisolator is totally redundant and over kill too – it’s input LED shares the same power supply as the output transistor! Remember the missing memo?

It was time to assemble the circuit. This is where the mad scientist dudes got really creative. On one half of a piece of acrylic, the schematic diagram was etched using the laser. This ensures n00bs get some education. And the remaining half had the circuit laid out in old-skool wire wrap fashion. Holes were drilled and connections were drawn (using the laser, of course) for the various components. Parts were inserted, and wires were soldered to make the connections. The result is what they call the PCB/Mounting Plate/Educational Schematic/Acrylic thing. Of course, exposed connections and wires are no good. So they made a sandwich consisting of a flat acrylic base, and a cut out frame in the middle to accommodate the wire connections and joints. All of this to light up an indicator. Because.

Thanks [JAC_101] from LVL1 for sending in this tip.

If you want to read more about LVL1 shenanigans, check out this post about their Rocketry group, or this post when Hackaday visited LVL1.

20 thoughts on “Laser Cutter Exhaust Interlock Is Silly, Educational, Useful

  1. This is how we learned electronics at many universities back in the 80’s and 90’s. I built a FM radio on a wooden board with brass nails and parts exactly like this directly over the schematic.

    The final exam of building an AM radio from scratch was more fun. I was given extra credit for adding in Upper and Lower sideband capability with the AM. I also had mine working at the 180 meter band instead of broadcast.

    Sadly they dont make EE’s do it this way anymore.

    1. “LVL1 is located near a place that turns pigs into wonderful breakfast meats…”
      Not sure what your point is.

      I love the schematic etched into the plastic. I usually place a paper schematic inside whenever I build a black box, but this ensures it won’t get lost.

      1. “LVL1 is located near a place that turns pigs into wonderful breakfast meats…”
        Not sure what your point is.

        In some parts of the world, “Pigs” is a derogatory term referring to law enforcement. I didn’t catch the part about breakfast meat (which I love). I apologize for the confusion.

    2. From the article…

      “And even though LVL1 is located near a place that turns pigs into wonderful breakfast meats..”

      Nothing to worry about, unless bacon makes you sad.

  2. Yes, that note was in the referenced article but not pulled fwd into the review above… hence the confusion.
    My favorite bit was
    “…The crowd then remarked about statistics keeping, quantitative measures and raspberry pi. These wonderful suggestions were immediately suppressed and work on the indicator began…”
    which was also only to be found in the source article…..

  3. This seems silly, the pressure switch can provide the enable to the laser cutter directly. If you want to get fancy with indicators, just have an LED or strobe actuated by the NC terminals, so when the filter clogs up you have a visual indicator. The circuit is poorly designed and is analogous to the DVM with the useless fuse yesterday.

    1. This is just par for the course, looking at other LVL1 writings and projects. There’s no engineering like overengineering. At least not in a hackerspace worth its salt. ;)

  4. I was going to complain that they had unnecessarily crossed the wires over leading to the coil terminals – relay coils not being known for their polarisation – but then I looked at the rest of the circuit. Wtf, man.

    Was this an attempt to push the tide out in their parts bin?

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