I’m delighted by the clear plexiglas design. And having the mechanical assembly — particularly the extruder — put together really highlights how small this thing is. That’s not a bad thing — for a given build capacity, the smaller the machine is, the better.

Support Assembly

The extruder parts arrived as a bag of plexiglas pieces with their protective plastic coating on and a couple of bags of mechanical parts. Before using each piece, the blue plastic has to be peeled off.

There’s room in the CupCake for a bit of whimsy — the vertical supports that hold up the edges of the filament feed are shaped like and referred to as dinosaurs. Very cute.

It was a pain getting all the tiny blue plastic pieces off the inside of the laser-etched letters — but totally worth it.

Superglue

The left and right “dino” bases are made of two layers of plexi laminated together with superglue. I hadn’t face-glued plexiglas before, so I was curious how visible the glue joint would be and made a test patch with some scrap first. Interestingly enough, the glued area turns out to be clearer than the surrounding area — I think the glue filled in some of the scuff marks on the old stuff I was using.

Regardless, it did suggest to me that the glue marks would be somewhat visible, so I carefully daubed the glue in areas that would be hidden under the edge of a perpendicular piece, then clamped them for half an hour.

After removing the clamps, the glued pieces slid right apart, in contrast to my test pieces that I don’t think I could separate without shattering the plastic and gouging myself. My friend Mike Smith suggested the best explanation I’ve heard yet — the new plexi may have had a release agent on it, which I cleaned off the old pieces when I washed them to get the dust off.

Ideally I would have taken the pieces apart, cleaned them, and tried again. However, I’m a fraidy cat around superglue and wasn’t sure how to clean the (still wet) glue off the pieces so I could go wash them without somehow sticking them to myself in the process.

Instead, I clamped them overnight; and by morning, they seemed secure. I speculate that in the moving and sliding around, the liquid glue cleaned away enough of the release agent (or dissolved it more evenly throughout the glue instead of forming a barrier between the glue and plastic) that it was able to hold well.

Lesson: Wash plastic with soap and water before gluing.

The instructions had actually said to assemble the supports first, then glue the second layer on afterward. That sounded trickier to me, so I had laminated the two pieces in advance.

Here’s a good reason not to do that: Tightening the screws caused stress marks in the plastic and/or glue that were much more visible than the glue marks I had been concerned about.

Lesson: To avoid stress marks, assemble and torque first; glue second.

Motor and Pulley

The CupCake uses a toothed pulley (made for toothed belts) to grip and feed the plastic filament into the heater assembly.

The pulley has two set screws at 90° and the assembly instructions say to tighten the proverbial daylights out of them — but the motor shipped with only a single-flat shaft. If I’m going to bother tightening daylights, at least I’m going to do it with a flat for each set screw; so I filed a second one at the appropriate place.

An unanticipated advantage of having the flat not extend to the end of the shaft is that the pulley can be loose-fit for final positioning yet still unable to fall off the shaft. Slick!

The filament feed assembly is made of layered plexiglas to mount the different parts and to provide a channel to feed the supply filament. The motor mounts to the first piece, and the others bolt together in a big sandwich.

I mounted the pulley as far onto the motor shaft as it would go; but the first time I assembled, the pulley still didn’t align properly with the filament channel. I took the assembly back apart and shimmed the whole motor a little further out with a layer of washers (these particular ones not included) between it and its mounting plate and it aligns now.

I love the crystalline, Fortress of Solitude (albeit not spiky) appearance of the filament feed. The idler wheel — also plexiglas and not shown here — goes in the recess at the right, and (after shimming the motor) perfectly mates with the filament drive pulley and the filament channel.

The completed filament feed, sans heater.

The white plastic spacer is on the upper left machine screw because only about half of the screw is threaded; and without the extra thickness of the dino head, the nut can’t thread far enough to grip the sandwich. In fact, the other three just barely don’t thread far enough, but it’s not as noticeable.

The controller board mounts on the front using the four screws. The assembly instructions suggest threading on more nuts as standoffs to clear the protruding idler axle, then mounting the board, then mounting more nuts to finish it off.

In the midst of all this glistening plastic, adding a stack of silver-colored nuts didn’t appeal to me. I contacted MakerBot to get a quote on laser-cutting me some washers of the same thickness as the dino heads, and they seem amenable and I’m waiting on my parts. This will enable me to

1. Shim out the upper left plastic sandwich to the same thickness as the other three, so the white spacer isn’t needed and all four machine screws are even.
2. Shim out all four machine screws past the last little bit of unthreaded shaft so the nuts hold the plastic sandwich together tightly.
3. Build up a stack of clear plastic spacers as standoffs to mount the PC board, in my opinion more in keeping with the design of the rest of the device.

So for now, I’m leaving the PCB off until I can get my spacers.

Finally, it’s hard to see because everything is clear or white, but the center piece between the left dino front and back layers isn’t quite as wide as the thickness of the plastic sandwich, so there’s a bit of a gap (that only I would notice). Curiously, I think the center pieces are the same side on the left and right dinos, but the right dino doesn’t seem to have this problem.

Heater Assembly

The heater barrel is a DIY job, and the first step is cutting the nichrome to length (optimal resistance 6Ω; mine shipped at 8+Ω and required some trimming) and crimping on wire to feed from the controller to the heater.

The kit didn’t ship with wire, so I ran out to storage to grab some teflon-coated wire from Slim’s stash. I’d used teflon-insulated wire before while working on an avionics and test equipment assembly line and knew of its heat resistance. In quick tests, this wire’s insulation withstood a few seconds of flame without any noticeable deterioration and discolored after much longer than that. A good choice for connecting to a heating element.

(Insulated) nichrome wire wound around the heater barrel; Kapton “space” tape holding everything in place.

Thermistor added to extrusion head and lots more space tape. The painters tape on the PTFE barrel is just holding the wires out of the way for convenience as I wrap.

A note about this construction — it’s possible for the ABS to burn inside the nozzle, at which point it becomes impossible to get the ABS out of the nozzle by conventional means and you have to unscrew everything and soak it in acetone. (Thanks for posting all your exhaustive materials research, nophead!)

So I’m trying to keep the head as easy as possible to separate from the barrel, and I settled for one layer of tape around the thermister. Should be easy enough to undo and redo if it comes to that.

Insulated and ready to go.

Mounting the Heater

The heater barrel mounts to the filament drive via a mounting plate that bolts to the captive nuts in the plastic sandwich. Two of these things are not like the others; two of these things just do not belong.

The (black) 12mm M3 machine screws referenced in the assembly instructions are a bit too short to reach, and it looks like these two non-anodized screws were added as a last minute patch. No real harm done; and I’ll see if I can find some black hex-socket machine screws at the hardware store to replace them eventually.

Hm, anyone know where I can get black M3 washers???

And there’s the whole assembly, minus the aforementioned controller PCB while I wait for my clear spacers.

Don’t panic. If for some weird reason you need one of these, I have more where this came from.

It’s a little hard to see from these shots, but the case profile is a weird trapezoidal shape.

Physically large linear power supply; two main PCBs.

Lithium 1/2 AA cell from April of 1989. Rated for 3.6V and still holding 3.69V after twenty years.

Not sure why they used two PCBs (don’t tell me they really needed the extra 20 square inches), but it’s cute the way this one slides out.

Every one of these had its shield pins broken free of both solder joints. Looked like cold solder, but I assume it was just mechanical stress.

Voila! Four connectors for Cort. And a power cord for my brother, that I’m out of time to swap onto his pump tonight. Tomorrow, then.

I can’t tell that any of this stuff as still useful (which presumably has something to do with why it was out in the Dump in the first place), so it’s destined for disassembly, component removal, case reuse, and recycling. If there’s anything that strikes you as useful, throw a comment down below about what it’s good for, offer to pay me what it’s worth to you plus shipping costs, and I bet we can work something out. I’d love to see some of it go to someone who’d actually make use of it.

HP 13037 Disc Controller

This interests me because of the HPIB (GPIB) interface on the back — makes me want to bust out my old CBM system and see if I could get it going. But it’s not worth the effort just for curiosity.

I’m puzzled by the hole at the left end of the back. I’m guessing this was a controller for a (large) external disk drive and there’s a cable missing or tucked inside.

Case with Intel SBC-640 Power Supply

The blank front with RF connector and the gap in back with unplugged cables lead me to believe that something else used to be in here. The power supply reads 5V @ 10A, 12V @ 4.5A, -5V @ 1.25A, and -12V @ 1.25A. If one didn’t mind the weight of the giant transformer, it seems like it could still be a nice linear power supply.

Case and Panel Meters from Multi-Voltage Power Supply

Obviously stripped of its guts. I’m not sure I’m willing to part with it anyway — I really like those old panel meters.

Sangamo Electric Co. LC-1 Line Conditioner

When I saw “line conditioner,” I thought of AC line conditioning, but that’s obviously not what this is. In fact, I don’t know what it is. 600/900Ω inputs sound familiar to anyone?

I love the fold-down front door, the card cage, and the jeweled power indicator on the right.

General Dynamics Power Supply

This is a heavy, 23″ rackmount power supply with lovely captive rackmount screws. By the labeling of the connections on the rear, I assume it’s a floating power supply; so I’m a little puzzled by the front panel’s positive versus negative labeling of +12V @ .7A, -12V @ 5A, and -15V @ 7A.

Power One Modular Power Supplies in Cage

Cute modular power supplies mounted to cage rails. I’m actually a little tempted to keep and use this — after replacing the terminal block covers on the left two modules, where the AC power daisy-chains across.

The rightmost module is 5V @ 12A or 6V @ 12A:

And the left two modules are 12V @ 3.4A or 15V @ 3.0A.

Custom Power Supply

This looks like a homemade Slim job. I’m a little surprised there’s no onboard regulation. I haven’t bothered to check output voltage.

Maxwell Electronics Corporation 48VDC Power Supply

This adorable power supply is regrettably missing its tubes, and quite possibly more on the inside. It says it was made by Maxwell for the U.S. Department of Commerce, Civil Aeronautics Administration. It makes me wish I had a use for 48VDC (at home) so I could fix this up and have a nice warm tube glow in one of my racks.

Date Accepted: Jan 1959

It doesn’t look like much from this view, but there were four grocery-store shelving fixtures and several additional shelves full of miscellaneous old electronics and miscellaneous other things. With the shelves broken down into flat pieces, the contents completely filled Lawrence’s 15-passenger van, floor to ceiling, with all the seats removed.

Here’s the back corner after all the shelves and most of the storage contents had already been removed. There was a fair bit of Southwest Technical Products equipment back there, which is of no particular interest to me but considerable interest to a couple of other people I’m in contact with. I’ll be going through all the cases and boards, sorting into SWTPC versus other stuff, and cataloging and photographing the items for a separate post.

There were several coils of what I believe Cort referred to as aluminum hard line antenna cable, which he also said is outdated and of no further use. Lawrence will take drop it off for scrap metal recycling next weekend unless by some miracle someone indicates they think it’s still worth something before then.

This TI Silent 700 hardcopy terminal with the dual cassette drives on top really tickles me. This DigiBarn post suggests they could upload and download content over the terminal line. I learned to program on teletypewriters on a timesharing system, and I have a soft spot for hardcopy terminals. The cassette drives are definitely icing on the cake. And I think I have about a dozen more of those drives, loose, from Slim.

The “silent” in the name refers to the thermal paper, by the way, and I’m not sure I like the idea. Using a hardcopy terminal wouldn’t really be the same without the distinctive clatter of the DECWriter pins against the flat metal platen, and the almost anthropomorphic sound of the printhead sliding slightly to the right, to get out of your way and let you see what had just been typed, each time the terminal was idle for a couple of seconds.

Mission accomplished. Just a few non-electronics items left for Maeve to deal with.

Back home and unloaded, here’s what appears to be a campus A/V distribution patch cabinet. It has what I think are SO-239 connectors on the top (I’m not a radio guy) and 1/4″ sockets on the bottom. I’d be happy to part with the SO-239 panels if someone had a use for them.

Although it looks messy now because whoever uninstalled it did so rapidly, the cables were very nicely routed and carefully bundled and laced with waxed string, an art that I fear has become lost.

Finally for today, my first treasure of this trip: an HP 122AR rackmount oscilloscope. Just last week, I was talking to Jeremy about installing a power inverter in my cargo van and setting up a gig box with a rackmount scope and some other tools for portable/mobile electronics troubleshooing and repair. If this works and it’s not too dep, it’ll be lovely for that! (Of course, I’ll have to make it clear that the gig box needs to be treated with care and not dropped out of the side of the van, but I think I can handle that.)

Looks like it has two channels, which is cool. For this application I’d be even more excited if it had two axes (great for troubleshooting vector arcade games, and I do have a couple of two-axis scopes already, just not rackmount), but I’m thrilled with what I got.

Now I need a few sunny evenings or Saturdays to photograph and catalog the rest of what we brought back. There’s a lot of stuff that looks no longer useful to me, and I’ll be willing to work something out to get it into the hands of the right people if it’s still useful to someone else, so I hope to post good pictures and descriptions in the coming weeks.

Our air conditioner was low on refrigerant and the blower fan motor may be running slower than spec and not moving enough air. Between the two problems, the expansion coil inside the furnace housing would ice up, over a few hours completely blocking the airflow and preventing any meaningful heat exchange. I’d then have to switch off cooling mode and run only the fan for a few hours to melt the ice.

On a weekend when I was home all day, I discovered that I could keep the house fairly cool by setting the blower fan to run all the time, manually monitoring the airflow out the vents, and cycling the AC off when airflow was restricted and back on when it opened up. Which sounded like a perfect job for a microcontroller.

Introducing the scungy anemometer, or Airduino v0.1, for short. Also introducing real-life code using the Arduino’s external interrupt pin(s).

Measuring Airflow

My thought was to stick a propeller into the airflow and measure its rate of spin with an optoreflector. Some people have used brushless PC cooling fans and measured the electrical impulses, but I didn’t have any. And I tried blowing air into spare PC (DC motor) fans, but their permanent magnets made them all too stiff to turn.

Knowing I wanted something light and easy to move, I folded aluminum foil into a four-layer rectangle for rigidity, twisted it to make a propeller shape, and stuck a pin through the middle. Holding it in front of an AC duct, it spun freely and rapidly, so I figured it was a good start.

Next, I hoped to use an optoreflector pointed at the propellor to measure rate of spin. An optoreflector has an LED (usually infrared) and a matching phototransistor pointing in the same direction, so it can detect when the light is being reflected off a nearby object. (An optointerruptor has the LED and phototransistor facing each other with a slot between them, to register when something passes through the slot. I don’t know of any commercial optointerruptors with a slot wide enough for my foil fan blade to pass through.)

I had this big bag of optoreflectors and optointerruptors from Slim, so I figured I was golden.

And none of them worked for me. All of them that I tested had a resistance of about 10-100MΩ through the phototransistor, with very little variation between lit and unlit conditions. [See comments for discussion and correction.] I already expected to have to use an op-amp to boost the signal; but on my scope I was seeing about as much 60Hz interference as signal, so I didn’t see much point in going further.

I figured surely I must have some other optoreflectors around the house, but I couldn’t find any. Failing that, maybe I could find a separate IR LED and phototransistor to make a giant optointerruptor? My friend Joel reminded me that I had some in my Boe-Bot, but their receivers turned out to require a modulated 38kHz signal, and I didn’t want to mess with it. I had an ancient IR LED / phototransistor pair from Radio Shack, but (according to my IR detector card) the LED was burned out. (I didn’t know they were still carried, and I should simply have picked up another pair, but it was late in the evening and the store closed. I’ll get myself another pair to play with later.)

I really wanted to get this thing going, so I grabbed a CdS photocell and a green LED. The photocell (with the red and yellow heatshrink in the upper center of the picture below) was already soldered to a three-pin header with a matching resistor for a demo I had given, so I plugged it into a breadboard, bent it over, and aimed it at the LED. I made a propeller mount from a piece of wire and hot glue, and voila! One ugly optointerruptor.

Amplification

That gave me a varying DC voltage with (if I recall correctly) about .1V peak-peak. I wanted to use a digital input on the Arduino rather than having to constantly read A/D conversion, so I needed to amplify the signal to as close to 0-5V swing as possible.

Noise I was seeing in the signal — probably variations in visible room lighting that the photocell was picking up, and which I might have been able to mask out by enclosing the whole board in heavy paper — made me nervous about using a comparator or running the op-amp at infinite gain; I feared I’d end up counting lots of twitches in ambient lighting conditions. I really wanted to have a smoothly varying analog signal as the propeller blade entered the light path, completely blocked the light, and exited, to use a Schmitt-trigger to digitize the signal (more on that in part 2).

I used one op-amp of a TL084 (low-voltage op-amp, so I could use it with my single +5V supply instead of the usual ± supply) in a capacitor-coupled, inverting configuration to boost the signal. I found experimentally that a gain of about 40 gave me a good, consistent read of the LED without being overly sensitive to the random noise.

Next, digital connections and Arduino interrupt programming.

Temperatures must have been quite a bit higher than expected; because although there’s some ice on trees, all the freezing rain that hit the ground stayed wet and is draining away.

So here I am at home, waiting for more limbs from my neighbors’ tree to fall on my garage, and catching up on some electronics.

Another Weekend of Cleanup

Cort and I went to Pittsburg this past weekend to help Maeve clean up more of Slim’s stuff. The focus this time turned out to be books, but we each plundered other areas as well.

I adore these vintage resistor storage cases. The drawers are about 1/2″ high — you don’t need much more than that to store resistors — and they’re totally dreamy. (Um, yup, I’m a geek. )

Engler Hour Meter

Cort and I found this on a shelf in Slim’s garage:

It’s an Engler Instrument Company hour meter model 10N, and I think it’s absolutely gorgeous.

It wants to be built into a rich walnut case for something. (I’m not an active steampunker, but I definitely admire real and faux antique gear with wood and brass and glass and gleaming chrome and flicking needles with paper scales behind them.)

Give it 110VAC and it counts hours. The case is riveted shut, so there’s no resetting it. Still, it wouldn’t be that hard to run it long enough to reset — only about 35 months. (I’m going to need a good reason to do that, though . . .)

Slim’s Microcontroller Development Drawer

I’m not sure which cabinet this came from, but Maeve had taken a whole drawer full of Slim’s microcomputer and microcontroller development gear out to the garage. Cort and I picked through it, boxed it all up, and brought it home.

Some of the detail that follows is as much an inventory for Cort and me so we know what we have and where it’s packed, as it is intended to be of general interest.

Lots and lots of microcontrollers and related chips: Two sticks of TL064 op-amps, three sticks of PIC16C55s, three of PIC16C56es, two of PIC16C57s and two UV EPROMable chips, two sticks of PIC16C71s, a stick of ISD 4004-16MP 16-minute audio recording chips, a stick of ADCs, a bunch of miscellaneous Mozer Digitalker chips, an XC68HC705K15, and a couple of MC68HC811E2INs.

Circuit Cellar RTC52 and RTCIO kits, unassembled. I was never a subscriber, but these appear to have been the foundation of many Circuit Cellar control and automation projects; see for example this touch-tone remote-controllable home automation system from 1991.

A PICBASIC development kit.

Various microcontroller development boards, at least two of each, and heavily biased toward Motorola.

An M68HC705KICS programming board, adorably fitted in a box with cutouts for the power leads and ribbon cable, so it never has to leave its nest.

A RAM board and two MP-09A CPU boards from a Southwest Technical Products Corporation 6800/6809 computer, circa 1978. I would really like to find a good home for these with a SWTPC collector. I think there’s a related chassis in storage as well, which I’ll dig out next time.

Couple of LCD screens in “widescreen” format.

A very funky, battery-powered speed synthesizer board. Cort said Slim picked this up somewhere (probably at the Dayton Hamvention) and the two of them (particularly Cort) poked at it for a long time figuring it out. They were able to get it to make noise, and it has both recorded phrases and a phoneme generator, but they never found any documentation about the dictionary and weren’t willing to spend the time to catalog it by trying every address. Cort also said it draws half an amp.

And a very large, datacenter-style pushbutton switch. Sweet!

For all that effort, we basically got the van cleaned out and the family room counter cleaned off. We could tell we’d made a dent, but there’s obviously a huge amount left to do. Nevertheless, Maeve was overjoyed at the work, and I think the most important thing we accomplished was helping her reduce how overwhelming the job seemed to be. Plus I got her DVD player, worldwide and NTSC-only VCRs, and Tivo hooked up to her TV so she can watch movies again.

As we sorted, we grouped things into six rough categories:

• things that Maeve will use herself
• expensive items that she should sell (possibly to one of us, possibly elsewhere)
• miscellany that one of us was interested in
• miscellany to take to the radio club grab pile
• stuff (mostly non-electronic) that won’t bring enough money to be worth the hassle of selling, but is still potentially useful to someone, to take to the thrift store
• trash

Each of us took home a few things, and I have others to talk about in due time; but the one that impresses me most was Slim’s prototyping station. Cort often talks about how important it was to Slim that people use things and how ready he was to give things away to people who would actually use them.

The radio guys aren’t really building things these days; Cort said that he and I are the only ones doing circuit design, with me doing the most right now. Because of that, Cort insisted that I be the one to take the station. I am very honored; and with great honor comes great responsibility.

The Station

Slim designed and built this himself. To me, it not only is a very impressive piece of work, but also reflects a lifetime of experience prototyping circuits and knowing what features are useful to have at hand. A station like this should come with a manual, and it’ll take me some time to figure it out and become fluent with everything it offers.

Myriad Connnectors

Starting at the top, the station has a multitude of connectors: DB-25 male and female, a card-edge socket that reminds me of my VIC-20 days, 1/4″ and 1/8″ jacks, barrier strip, RCA, BNC, and binding posts.

Each connector breaks out to well-labelled wire sockets in an area near the left of the front panel. These pin sockets are a Slim signature item — he used them on all of his breakout and prototyping stations, and I’ve never seen them anywhere else.

Next to the connector area, in the right of the photo, is an area for a signal generator that looks like it wasn’t finished. Based on some conversations I had with Slim about signal generators, my guess is that he intended to take the board out of a commercial unit, embed it inside the case, and extend its controls to the front panel, rather than construct his own from scratch.

Power Suppply

At the far left of the front panel are power supply connections providing variable + and – voltages and dual +5V supplies. If I’m following correctly, the two 5V supplies run to the ends of the rail above the breadboards, and are jumpered down to the left and right breadboard sections from there.

LEDs

In the upper center are two six-digit sets of seven-segment LEDs. The lower set appears to be broken out for matrix drive (labelled Digits 1-6 and Segments a-g at the left), and the upper set appears to have integral decode/drive (individually labelled A-D and D_p under each digit). There’s also a set of sixteen LEDs for individual use.

Microcomputer

The upper right corner has a microcomputer section with a 24-pin ZIF socket for EPROMs, selectable between 2708 and 2716 (this is old school) and presumably a microprocessor hidden behind the panel. Given the PIA labels, I’d guess it’s a Z80, but it could be something else with an external PIA chip as well.

Everything Else

That’s all the closeup pictures I took, but there are a few more features I’ve already figured out. The row of black knobs across the center are potentiometers of commonly useful values, broken out to pin sockets underneath each one. The row of tracks between the pots and the breadboards delivers power and also has four buses labelled A-D.

Above the tracks are wire sockets for the switches and pushbuttons across the bottom of the case. There appear to be six logic inverters. And at each end are two sets of LEDs labelled H (red), L (green), and P (yellow) — I assume logic probes showing high, low, and pulse.

And of course a breadboard, generously sized, with a bunch of parts still on it. It has a couple of TL064s, Slim’s and Cort’s favorite op-amps, but it doesn’t look like it’s really a circuit in development. It looks more to me like it might be leftover parts that he was moving out of the way.

Using It

My challenge now is to learn to use it effectively. I always have enough clutter on my workbench that I have preferred using small breadboards and pulling out only the parts and connectors I need at the moment. On the other hand, the benefit of a prototyping station like this is always having everything at hand, saving the time of having to dig out the right connectors and displays.

It’ll definitely take some to get used to, and to determine which method really works best for me. Maybe eventually, it’ll inspire me to build my own comprehensive station that’s just right for me; and with Cort’s help, hand Slim’s station down to the next generation of experimenter.

Here’s a project that I’ve been kicking around for a long time (three years–I guess that’s not so long compared to some of my projects ) and finally built–a battery meter. My friend/enabler Slim Cummings in Pittsburg gave me a couple of surplus 3-1/2 digit, .2V panel meters, and I thought they’d be perfect for testing the freshness of AA and AAA cells.

Meter

The meter was the inspiration for the project. It has a 3-1/2 digit (a 1 plus three 7-segment digits–1888) display, a configurable decimal point, and an Intersil ICL7106CPL LCD/LED Display, A/D converter chip. You give it 9V supply, a jumper for the decimal point, and a voltage input; and it samples the voltage and drives the LCD. It’s a very nice package that just begs to be used for something interesting.

Tester Case and Battery Holder

The physical aspects of the project actually took much longer than the electrical. First off, I wanted to find a case with the following characteristics:

• The case would be held in portrait orientation.
• The meter would fit across the width of the case, with the battery holder below it.
• I could fit a 9V battery inside the case to power the meter.

I figured I’d find a plastic project case from Radio Shack with a 9V holder in one end and enough room for everything else to fit . . . no such luck. I figured I’d find something in my junk bin that I could reuse–I was coming close with some old and broken copper-to-fiber media adapters, but they weren’t quite right. Finally I stumbled across the idea of using the plastic case from a data backup tape, and I rummaged around until I found this KAO 8mm data cartridge case.

I’m not wild that it’s translucent–I don’t like seeing the guts of things when I’m using them–but it’s the perfect size. The meter exactly fits across the width, the 9V battery exactly fits in the thickness, and it’s in portrait format. Plus I guess it’s kind of cute opening the case like a cassette case to change the 9V battery.

I picked up a single AA battery holder at Radio Shack a couple of weeks ago, and had to mod it a bit to fit it onto the case the way I wanted. The leads originally routed out holes in the ends of the holder, but I wanted them to go straight down through the case. Fortunately, there was already a hole underneath the terminal at each end (you can see the one at the right end of the above picture), and I was able to fish the wires through and tug them into position to make it work.

The holder also had tabs curving slightly around the front, to help hold the AA cell inside. Since I want to be able to insert and remove cells quickly, I removed the tabs by scoring the plastic flush with the rest of the front of the holder, then snapping them off. I also confirmed at this point that a AAA cell would make contact with both ends of the holder, even though it wouldn’t be held as securely. (AAA cells are shorter than AA cells, as well as thinner.)

I drilled mounting holes in the case for the meter and battery holder, as well as holes for the wires to go through. The plastic was so soft, I didn’t even bother chucking the bits into my drill for most of the holes–I just turned the bits a few rounds with my fingers and I was through the case.

I did get to use my stepped drill bit set to enlarge the meter’s mounting holes–the bezel’s posts have larger-diameter plastic shoulders at the base, my mini-drill doesn’t have bits that large, and the stepped drill bits do an excellent job of enlarging while remaining concentric with the pilot hole.

The last tricky bit of work with the drill was the big ugly hole in the center of the picture of the drilled case. I needed a power switch for the meter, but I was loath to have to have to slide a switch or press a button every time I wanted to use it–I wanted it to spring to life when a cell was inserted to test. Plus for reasons to be described a bit later, I planned for a pushbutton on the front already, and I didn’t want to have two.

The solution was simple enough–a pushbutton switch inside the battery holder, actuated by the insertion of the cell itself. I salvaged a tiny microswitch (“nanoswitch???”) from a dead CD-ROM drive (a limit switch from the optical sled), reamed much too large a hole in the case and battery holder, poked the switch in from underneath, and hot-glued it in place.

Meter Wiring

The meter board is built for a range of 0 – .1999 (.2) V, but has pads to set the placement of the decimal point and to provide your own voltage divider to adapt for other ranges. The documentation gave the resistor values to adapt for 20V and 200V, from which it was easy enough extrapolate the nominal values for 2V operation: 9MΩ and 1MΩ. Well, I have 1MΩ resistors on hand, but not 9MΩ, and certainly not precision.

Fortunately, 9:1 ≅ 10:1.1, so I put a 10MΩ resistor into the pads for R_B (upper left) and chained a 1MΩ and a 100kΩ in series between the pads for R_A. (Those lap-soldering skills from a summer of module assembly at IFR Systems do come in handy.) Also fortunately, the calibration potentiometer had a generous range, so I was able to work around the 1% difference from the nominal ratio.

I also guessed (correctly) that the proper position for the decimal-select jumper was P1, which was missing from the voltage range chart.

Assembly

I had one more set of components to add, but I couldn’t resist wiring it up to see how it worked so far.

I soldered the 9V battery clip’s ground lead to the ground connection at the lower left of the meter board, the positive lead to the microswitch glued into the AA holder, and the normally open (NO) lead from the microswitch to the supply connection on the meter. I also soldered the AA battery holder’s leads to the V_in connections at the upper left. If you look closely enough, you may see that I just tack-soldered them in place with a lot of exposed wire a the end; I plan to come back and organize the wiring more carefully, and didn’t take a lot of extra effort at this point.

Meter in Action

And it works as planned! Not that there was much surprise, but it’s still nice when a project comes together. I was also pleased that the (undocumented) position of the decimal point was correct. Further, I was hoping to avoid cutting a large hole in the box for the panel meter; and I find it adequately legible reading through the nearly transparent case, without a hole.

I put a AA cell into the holder, the switch activated beautifully, the meter sprang to life, and I had a reading of the AA cell’s voltage. I measured the cell’s voltage in situ with my best voltmeter, calibrated the panel meter’s reading via the potentiometer on the back, and measured with my good meter once more to make sure the voltage hadn’t drifted while I was adjusting. Good enough!

Load Testing

Finally, I drilled two more small holes in the case, poked a pushbutton switch through (in the lower left of the above photograph), and wired a 10Ω resistor in series with the switch, and the switched resistor in parallel with the AA holder. From my first inspiration for this project, I’ve wanted to be able to test cells under load as well as unloaded. I find that some cells I’ve owned–particularly, I believe, when they’ve lost capacity due to age rather than use–will show a relatively high unloaded voltage even though they have very few mAh left. I very specifically wanted to be able to test under load to identify this condition.

And it’s proved itself already. The cell shown under test reads 1.163V, which is by no means new, but might still appear to be usable in some types of devices. But when tested with a load, it drops immediately to ∼.8V and continues to fall toward .7V–not nearly as promising. In contrast, another cell I’ve tested measured ∼1.2V unloaded, but still ∼1.1V under load–very likely quite usable yet.

Sorting Batteries

I’ve already switched to using NiMH cells for all my projects and consumer hardware, but I have a number of alkaline AA and AAA cells around the house from the old digital camera and the Visor PDA, with no good idea which are fresh and which need to be discarded. (Y’know, it’s such a pain to test cells with a voltmeter and only two hands.) I can finally conveniently test and sort them into four categories:

• Unused: Save for when I don’t have any rechargeables ready, or give with battery-powered gifts to nieces and nephews who don’t do the whole “rechargeable thing.”
• Still strong: Save for my LED flashlight, which seems to get quite a bit more life out of used cells than do incandescent lights.
• Weak: An interesting problem. They still have some energy stored, but not enough to use in traditional portable devices.

  I’m planning to build a “Joule thief,” a clever and tiny transformer feedback single transistor inverter that claims to be able to “provide a week of continuous low level light from a battery that would normally be considered dead.” Maybe I’ll end up with a bunch of “electronic candles” sitting around for the next ice storm; who knows.

  Update: Here’s another Joule thief project.

• Dead: Take to work and toss into the battery recycling bin. (And scrounge “weak” cells out of the bin to take home and make more “candles,” har har! Just don’t tell my wife that I’m stealing other people’s dead batteries now . . .)

Credit

A huge thank-you to my friend Slim, who gave me the panel meters that started this all; and who’s always generous with his vast experience and equally vast stores of electronics surplus.

Making a PC Board (PCB)

Last week, I had got the PCB layout done (and redesigned to correct an aesthetic error) for a single prototype digit of the clock. Next, I needed to produce an actual board to see how well the design worked, and whether it actually looked right in operation. I’m not willing to spend $60+ on a 3″x4″ board, so commercial production was out. EAGLE has a User Language Program (script) to generate router instructions for milling away the copper around your traces (instead of etching it away), but Joel and I haven’t taken the time to figure out how to output a format that his drill machine can read.

That left me with etching the board myself. I’m used to drawing the traces by hand with a permanent marker, and having discovered EAGLE’s checkbox for printing a mirrored copy of the bottom-side traces would have made it a whole lot easier to draw all the traces correctly. I recently ran across another web page describing an etch-resist iron-on process using plain magazine paper (which unfortunately I didn’t bookmark), and I thought I’d give it a try.

Cutting and Drilling the Board

First, I needed a board with the through-holes drilled, because I’m pretty sure it’s easier to match the traces to the holes by hand than to align the traces correctly to drill the holes on the machine.

I needed a 3″x4″ piece of single-sided, copper-clad board. I have a huge piece of board from my friend/mentor Slim in Pittsburg, who was using it to keep the rain off of tarps in his back yard (or something like that):

When I need to make small boards, I cut a strip off of the end of the monster in some standard dimension (even inches), then cut the strip to length as needed. The carrier is bakelite and very brittle, so shears don’t work like they do with fiberglass; thus when I had cut off my 2″-wide strip, I used a hacksaw blade. It was very tedious, and I was looking for a better method, so Saturday I cut a 3″ strip by holding down a yardstick guide and scoring a snapline with the corner of a cheap chisel. I scored most of the way through before snapping, and it worked so well I cut the short pieces to length the same way, rather than on my scroll saw as I had done previously.

I actually had plenty of opportunity to practice, as I wanted to drill two prototype boards in case the first didn’t turn out, and I decided to drill the boards in a stack to save time, and I put them in the drilling machine upside-down (single-sided board, ‘member?), and I cut two more boards and got them right on the second try.

I’m only slightly ahead of myself here. Before making that particular mistake, I had generated an Excellon drill file out of EAGLE and took it to Joel’s house. DanCAM’s optimizer/translater didn’t like the format, so I compared it to another file I had drilled previously and hand-edited it into the same format. (This is on DOS using EDIT, mind you, because that’s what DanCAM wants to run under.) I think I’ve figured out how to make EAGLE generate DanCAMmable files directly, and I’ve written up the information on my EAGLE Circuit/PCB Layout Tips page.

Iron-On Decals

I knew you could purchase special “paper” that you could run through a laser printer, print the traces you wanted on your board, and then iron them onto the board and peel the paper away. In fact, Joel has a pack of this stuff that he’s been wanting to try for years, and asks if I want to test every time I’m building a complex board. I keep refusing, though, because I assume a sheet will only survive one trip through the printer, the boards I make are much smaller than the 8.5″x11″ sheets, I hate to waste the rest of a sheet, and I was leery of taping a smaller piece to a paper carrier.

So I was intrigued when I recently ran across postings describing a method I had heard of before: Print onto magazine paper (or overhead projector sheets). Supposedly the glossy paper releases the thermoplastic toner adequately when you iron it onto your clean copper board. With two (correctly oriented) copper boards on hand, it was worth a try. Plus I had a secret weapon: a stack of clean clay (glossy) paper salvaged from when I took out the trash and waste at a printing press, clear back in high school.

The first step was to clean the PC board that I was going to iron. I scrubbed it with 600-grit sandpaper to clean the surface and knock down the rough spots around the drill holes, then with 1500-grit to get it as smooth as possible.

I then printed the trace and pad pattern onto the clay paper, put it against the drilled board, and held it up to the light to align the pattern with the drilled holes. It turns out that my printer–an HP LJ 4M+ workhorse from Boeing Surplus that I’ve been using for years–prints slightly smaller than actual size, regardless of what kind of paper I have in it (so it’s not just slipping the rollers on my glossy paper). So the holes didn’t line up from end to end, and I had to cut the paper into three sections to get it to align well enough. I taped the sections onto the PC board so they wouldn’t slip, and I was good to go.

I ironed the paper onto the board as well as I could. In retrospect, I should have put a solid block or board underneath to support it from tipping and sinking into the ironing board’s pad, because the edges didn’t iron on nearly as well as the center. Although this picture is out of focus, you can see how large sections of traces are missing from the edges.

I found it intriguing that the only the front side of laser toner is black–the back side is white, as you can see on most of the traces above. Ha. Ha. That’s the surface of the paper carrier, of course, which stayed adhered to the toner even after soaking in water long enough to slip the rest of the paper off.

I drew in the missing traces with my trusty Staedtler marker, including touching up the gaps between the sections of paper I had cut apart. I etched in FeCl for about an hour, rinsed the board and touched up the marker traces again (the toner traces were still fine), etched a while more, and ended up with this, a fairly respectable little board.

Acetone takes both permanent marker and laser toner right off:

And it was time for assembly.