The Owad Laboratory

Unboxing the Laser Cutter

The Chinese 40W laser cutter, sometimes called the K40, has been around several years now, and prices have finally dropped below $400. After waiting for discounts to line up, I was finally able to purchase one last week for about $360 shipped. How bad (or how good?) is a $360 laser cutter?

The unit is larger than I pictured it, given the cutting size. The box is 37"x25"x16". With its weight and bulk, it was too large for me to get my arms around, so I slid it in the front door and unboxed it.

 

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BitScope mount for iMac

I've owned a BitScope BS10 for a few years, using it primarily as a logic analyzer. I recently bought the probe adapter, which makes it easier to connect standard probes, and more convenient to use as an oscilloscope.

 

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The Ham Radio Exam

I've been thinking, for quite some time, about getting a ham radio license. I've been going to hamfests (mostly for the computers) since middle school, but never knew anybody well who had an amateur radio license.

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3d Printer Switch with Octoprint & SmartThings

My MakerGear M2 doesn't have a power switch, and it isn't convenient to turn off its power strip, so I connected it to an Iris Smart Plug with a little power switch on it. That solved the problem, and also let me turn the printer on and off with Alfred, but tempted me to intergrate with Octoprint. Octoprint has a plugin, System Command Editor, that lets you execute shell commands from Octoprint's Power menu. That makes the Octoprint part easy - now it's just a matter of controlling a SmartThings device from Linux.

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Raspberry Pi & Nexdock: Bluetooth via the command line

I received my Nexdock today and have begun configuring a Raspberry Pi 3 to work with it. I wasn't able to find current instructions for getting the Nexdock keyboard and trackpad to work with the Pi using the command line, so I've documented the procedure that I used.

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Uses for fishpaper

Fishpaper is an insulative paper that used to be common in antique radios. It's often used to insulate transformers.

The history of the name is pretty interesting. According to Alvin G. Sydor:

In 1729 Stephen Gray made the discovery of the conducting and non-conducting power of different substances. Gray found that by using woven silk served as an excellent insulator. Some years later it was found that the paper industry could provide what was equivalent to woven silk. Later it was discovered that if the paper was saturated with fish oil its ability as an insulator was much improved particularly when used in harsh environments and high voltages.

Recently, I've been using it for fast and cheap electronics cases. This is one of my backup servers:

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Cleaning handles with a brass wire wheel brush

I bought a Remline tool chest at an auction on Saturday. I've been wanting to get something a bit larger than my current chest, and I couldn't pass up these handles:

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Sonar trumps eTape

I’ve given up on the Milone eTape entirely. I just couldn’t get it to work reliably. Instead, I decided to go with a RadioShack Ultrasonic Range Sensor as my backup method for detecting water. It’s mounted on the basement ceiling and will alarm when it detects an inch of water on the floor. The floor is sloped, so an inch isn’t nearly as bad as it sounds. It’s been working well. I’m leaning towards a pressure transducer for the main sensor.

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Calibrating Milone eTape

Milone's eTape is proving to be rather finicky. Per Milone's instructions, I have it installed in a 1" pipe, so that it can't stick to the sides. Readings fluctuate by up to 1/2", even with no change in water level. The eTape seems very sensitive to any sort of pressure. It needs to be suspended to give a proper reading. I neglected to suspend it during one test, and in an empty pipe, readings gradually reached 14", apparently just from the pressure on the bottom of the tape. Worse, according to this discussion, it appears that the eTape can be permanently damaged if it is submerged. That seems to contradict the Operating Instructions, which state:

The vent hole allows the eTape to equilibrate with atmospheric pressure and must not be submerged in the fluid to work properly. The vent hole is fitted with a hydrophobic filter membrane to prevent the eTape from being swamped if inadvertently submerged.

I've emailed Milone for clarification.

Update:

According to Chris at Milone, it's ok to submerge the vent hole, but submerging the connector tab will permanently damage the sensor - a detail I'd have thought would be worth mentioning in the Operating Instructions. The newer eTapes that come in tubes are sealed so that this isn't a problem. Chris says that bare eTape can be sealed by using RTV or Silicone II to completely cover the connector tab.

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Prototyping a Sump Pump Controller

Most mechanical relays and switches are rated for 1 million cycles or less. That sounds like a lot at first, but if you have a sump pump that runs every 30 seconds, that's less than a year. Lowes used to sell a sump pump with a lifetime warranty. Every year, the manufacturer would mail me a new switch, and about every three years, a new pump, until they finally insisted on refunding my money.

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