Holiday Special 19

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When I posted my projects for the RF Project 14 in November, I mentioned that things might get busy, meaning I would not have much of a chance to post more projects. Well guess what? I was right! The Christmas-New Year period was exceedingly busy as I blogged on my own personal blog and tried to finish a few different projects that I have always wanted to do. Seeing that the Holiday Special Project14 deadline is coming up, I thought I'd do my best to cobble together a short project.


When I think of holiday periods, I think of gifts. When I was a child, one of the toys that people would play with is an Etch-a-Sketch - a board with some magnetic material that turns dark on the action of the magnet, which is suspended by cords along two axes with two controls on the front that control the X and Y axis motions independently. Using this, one could draw some rather simple images without needing paper, or pens. I never had an Etch-a-Sketch as a child, but then again, I was never really artistic anyway.


But then, just as the holiday season approached, I got news that I was awarded the B&K Precision / Sefram DAS240-BAT RoadTest review. Just two days before new year, the unit arrived, which got me thinking ... could this become an expensive modern digital Etch-a-Sketch? The answer was yes!


Building the System

Lucky for me, the DAS240-BAT supports direct measurement of resistance as it has an internal bias generator and the unit is capable of plotting in X-Y mode. All I have to do is supply the resistance.

Rummaging in my junk box, I found two new 500-ohm linear carbon-track long-stem potentiometers. I soldered a wire to one end of the track and the wiper and covered the connection in heatshrink. I then wired it to the input pluggable terminal block with the resistance across the +/- connections and the bias tied into the negative side as instructed by the manual.

I twisted the wires for some noise suppression, while plugging it into the 20-channel input module. Using some Blu-Tack, I stuck the potentiometers down to the table so they could be manipulated safely and then grabbed the camera.


In Action

I'm not much of an artist, nor have I used an Etch-a-Sketch before, but I tried my best to do a project with heart, by literally drawing a heart. Then I decided to try and draw my name ... I guess I don't have much finesse when it comes to turning pots ... as you'll see in the video

But I suppose it could be improved if I had used higher-quality 10-turn potentiometers as the 270-degree range of these pots combined with the mechanical backlash means that it's hard to get it to move precisely. The same sort of set-up can be used with a voltage source and infinite persistence in X-Y mode to do the same thing on an oscilloscope.



It's portable, it has an X and Y control and it draws an image. But it's not an Etch-a-Sketch ... it's a sophisticated, expensive piece of test equipment being tested in a rather whimsical manner. It's a pretty expensive way to get Etch-a-Sketch-style functionality, but it does work and it took all of about an hour to complete (from ideation through to uploading the blog and video). A project with heart? Maybe. A holiday project? Definitely.


It's also a bit of an experiment of mixing a Project14 with a RoadTest - within the next month or so, the full RoadTest review for the B&K Precision / Sefram DAS240-BAT should be complete and published, so I hope you look out for it as there's been a lot of interesting findings to say the least.