Having gotten my camera out to take reference photos during a work field trip to the zoo, I took the opportunity to snap some pictures of the TINI and the meter collection. These have been added to the original Meter Thing project post.
The ‘Meter Thing’ — to be granted a better name when one occurs to me — is a project to display on a set of vintage analog meters several numeric data (or data that can be turned into numbers) scraped from the Internet.
The heart of the beast is an older model TINI, a little Java computer with Ethernet and loads of I/O, all in the shape of a 72-pin SIMM — roughly the height, width and maybe a third the thickness of a pack of gum (although newer models use the DIMM form factor). This sits in an extremely simple breakout board, which basically just provides a RJ45 network jack and a breadboard-compatible set of DIP pins for all 72 conductors on the SIMM. The meters I bought in a lot of ten on eBay. They are all from different sources, are different sizes, and have different units and scales displayed.
The first challenge is to generate the analog signal for the meters. My original idea was to use 1-Wire digital potentiometers. The TINI supports 1-Wire exceptionally well, which is not surprising, as it has invented by the same people. 1-Wire would let me add meters as needed, just attaching them to the 1-Wire bus; I could then direct data to them by the unique ID of each 1-Wire potentiometer.
The problem with the digital potentiometers is the lack of range. Using the potentiometers to drive the analog meters directly did not give me the even coverage I need. The meters, regardless of their displayed units, are ammeters. Adjusting the resistance gives me a reciprocal curve (if I’m using the term correctly): x/1, x/2, x/3, et cetera.
I need some sort of ‘real’ digital/analog conversion; either PWM or some more sophisticated DAC chip. 8 bits of resolution are probably enough; if a meter has an arc of 60 degrees, that gives me increments less than half a percent. I have a couple of candidates in mind.
More background on this project and its current status to come.
This project is actually sort of a sub-project; it will later be used to drive more interesting things.
This is my first attempt at an L298 H-Bridge motor driver board. It is based primarily on some sample schematics from the L298 data sheet; some inspiration was also gleaned from other similar projects available on-line. This will also be my first attempt at etching a PC board, which is a little daunting.
The design is fairly straightforward; it isn’t much more than a breakout board for the L298, plus the minimal handful of additional parts to support it. I’m going deliberately simple in order to keep it as generic as possible; I originally bought my L298 ICs with the intention of providing forward and reverse for a pair of standard DC motors, but it now looks like my first application will be driving a bipolar stepper motor.
Introducing the Clock Project!
‘The Clock Project’ (as reads the label on the plastic box in which its parts reside) is something I started quite some time ago. I had been trying to think of some sort of object to create, something primarily artistic but also with some actual function. My original idea was to build a coffeemaker, but all my sketches of things I could build ended up looking like drug paraphernalia – while that’s arguably what a coffeemaker actually is, it really isn’t my style. I abandoned that idea and started thinking about building a clock.
The clock is going to be driven by a 1RPM timing motor, with a train of gears reducing that to minutes and hours. My plan is to have different faces for seconds, minutes and hours, as opposed to the standard system of coaxial hands on a single face. I don’t know why the standard clock design is like that; it seems to add unnecessary complexity, both in design and use. It’s a bit abstract to have two completely different numbering systems on the same face. My intention is also to have the clock rotate the face itself rather than move hands. This also seems like a better design; even lightweight hands are inherently off-balance, at least as traditionally implemented.
More to come, once I get some images rendered and web-ready.
This blog has lain fallow for too long, so I’m just going to start over. I’ve started (and abandoned) a lot of projects since I began to set this up, so anything here is painfully out of date. I’ve finished almost all of the site’s re-skinning, but there are a few odds and ends yet to be done (I have not yet touched the PHP).
It seems like a good time. Two-and-change decades of school permanently impressed upon me the feeling that September is a time for new beginnings.