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Archive for May, 2013

Makergear M2: Platform Stabilization

The M2’s build platform consists of an 8×10 inch glass slab atop an aluminum spider, all supported by a trio of fairly stiff springs. Back when I was experimenting with excessive acceleration, I inserted some silicone rubber cylinders to boost the spring constant and stabilize the platform

The same vibration isolators that provided the vacuum cleaner’s floor brush rollers came through again:

Silicone rubber pads for M2 platform - punching

Silicone rubber pads for M2 platform – punching

I removed the screws and springs one by one, tucked a cylinder inside the spring, and reinstalled it:

Silicone rubber pads for M2 platform - installed

Silicone rubber pads for M2 platform – installed

The trick is to park the nozzle near the edge of the platform where it will rise without the screw holding it down, measure the distance twixt nozzle and platform, lower the platform by a (known!) 50 mm, install the cylinder, raise the platform, then tweak the screw to put the same distance between the nozzle and the platform as you started with.

This probably doesn’t make much difference with the default 3 m/s2 acceleration, but up around 10 m/s2 it seemed wobbly. No suprise: that’s over 1 G of lateral acceleration and the platform weighs a pound or so.

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Hexagonal Chain Mail

Everybody at the Squidwrench Show-n-Tell loved the chain mail. I printed up a sheet of Ablapo’s hexagonal chain mail before the show (because it takes forever) and it came out very nicely on the M2’s larger platform:

Hexagonal Chain Mail - on platform

Hexagonal Chain Mail – on platform

The first layers sprinkle a bazillion little shapes all over the platform:

Hexagonal Chain Mail - first layer

Hexagonal Chain Mail – first layer

It makes a nice doily for my desk lamp:

Hexagonal Chain Mail - lamp doily

Hexagonal Chain Mail – lamp doily

The odd blue coloration must be an optical effect, because it’s not visible on the black PLA.

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3D Printing Show-n-Tell

So the local hackerspace put on a show in Highland and, being the guy with the 3D printer, I volunteered for a few hours of stand-up comedy.

A pile of stuff provided talking points:

3D Printing This Way - with clutter

3D Printing This Way – with clutter

Four pages of solid model images on nice glossy photo paper let me talk about what must happen before the plastic emerges:

I loves me some OpenSCAD modeling, yes, I do…

Signage festooned with sample critters dragged ’em in off the street:

3D Printing This Way - signs on post

3D Printing This Way – signs on post

The printer produced a steady stream of tiny owls:

M2 - Mini owl on platform

M2 – Mini owl on platform

And the ever-popular whistle:

M2 - Whistle on platform

M2 – Whistle on platform

A good time was had by all!

3 Comments

LED Output vs. Current: Efficiency Loss

Some data points from that circuit produced this graph:

LED Output vs Current

LED Output vs Current

Relative to the output at 5 mA, the efficiency drops off pretty much linearly:

LED Efficiency vs Current

LED Efficiency vs Current

That’s computed as the ratio of the actual light output to the output at 5 mA scaled by the current ratio.

So putting the screws to the LEDs does produce more light, but not quite as much as you’d expect. Above maybe 40 mA, it’s not worth the effort.

Now we know…

 

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LED Driver + Zero-bias Photodiode Amplifier

This may come in handy for something, like measuring LED output:

LED Output Tester - Schematic

LED Output Tester – Schematic

The LM324 converts the input voltage to an LED drive current, scaled by the sense resistor and the gain of IC2B to 25 mA/V. The feedback loop closes through the MOSFET and C6 rolls off the response, so there’s a nasty overshoot on the leading edge of input pulses where the current increases faster than the op amp can tamp it down:

Red LED - 25 mA 14 uA

Red LED – 25 mA 14 uA

The LM356 acts as a transimpedance amplifer to convert the photodiode current to voltage. The PIN-10AP specs say it should operate in photovoltaic mode with zero bias and that more than -3V of bias will kill the photodiode; the LM356 should hold its inverting input at virtual ground, but the two 1N5819 Schottky diodes enforce that limit. There being zero volts across the diodes, they don’t leak in either direction, so it’s all good.

The circuit is an embarrassing hairball on solderless breadboard, so use your imagination…

You could mash this together with the LED Curve Tracer, although you’d want better low-current resolution from the Arduino output.

4 Comments

One Problem With Electronic Medical Records

This seems innocent enough:

Medical eRecord Security

Medical eRecord Security

Of course, that laptop:

  • Runs Windows
  • Has unused USB and Firewire ports
  • Has active WiFi networking
  • Doesn’t have a screensaver timeout
  • Was left alone with a patient
  • Is not locked

I mentioned to my doctor that, if I were of malign intent, I would now have complete control of every PC on their network. That didn’t make much of an impression, as the same thing happened on my next visit.

Of course, moving to electronic records makes a lot of sense, but if you think they’ll be any more secure than any other online personal information, you’re wrong.

12 Comments

Garden Sprayer: End of Life

The hose attached to this garden sprayer had failed last season, but the hose fitting had become one with the sprayer. Soaking it with penetrating oil for far longer than seemed necessary didn’t help, so I tried brute force:

Garden sprayer hose fitting

Garden sprayer hose fitting

After convincing myself that wasn’t going to work, I cut the fitting off and tried the old standby of collapsing the threaded shell inward with a small punch:

Garden sprayer - rolled-in fitting

Garden sprayer – rolled-in fitting

That didn’t work, either: the shell really had become one with the sprayer.

As it turned out, the plastic sprayer body had begun to crack in several high-stress locations and would shortly become Yet Another Project. I cut my losses and tossed the hose and the sprayer.

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