I recently ran across on Craigslist a

Bad horsie 2 that was plugged into the wrong power supply and messed up, and needs some minor electronic work.

I was intrigued by the challenge (I’m such a sucker for broken things, dang it) and bought it. When the seller and I exchanged the pedal for my cash, he remarked that he read on a forum that it probably just needed a resistor changed, and that if I were handy with a soldering gun I could probably do it myself.

Uh huh. Resistor.

Let’s dig in.

The circuit board has a hole in the top for a foam battery “cage” attached to the enclosure, something clever that I haven’t seen before. And it had no obviously damaged components.

Testing the Power Supply

Like most (all?) guitar pedals, the input jack is a switching jack — the middle leaf doesn’t contact the plug, but is a normally-open switch in the power supply circuit so the pedal is powered off until the guitar cable is plugged in.

Tracing connections on the solder side reveals an interesting tidbit — the external power supply jack is not switched; only the battery is. According to the one-page owner’s manual, the pedal only draws 16mA; so (A) it should last a long time on a 9V battery, and (B) the pedal’s current draw is probably insignificant compared to the inefficiency of the wall wart.

The power supply jack is also switched — the lower and right terminals are normally-closed, powering the pedal’s positive rail from the battery by default but disconnecting the battery when the external power supply is used.

Finally, both the battery and power jack run through a series 1N4003 diode to protect the pedal from improperly-connected power sources. If this pedal was damaged by being connected to a wrong source, it was not merely wired in reverse — that would have been blocked by the diode. It must have been connected to a higher voltage than intended.

Since I didn’t know quite what to expect from the pedal and didn’t feel like setting up an instrument and amp to test it, all of my troubleshooting was at a purely electrical level.

With a battery connected and a plug in the input jack, I measured .87V across the battery terminals, where I should have had nearly 8.4V from my NiMH 9V-form-factor battery. I also measured a fairly low resistance across the two power leads (with power disconnected). Something in the circuit had shorted and stayed shorted (instead of blowing open); and either way, it should be fairly easy to find once I knew what I was looking for.

Removing ICs

My experience with circuits damaged by power surges or other excess power is that it’s almost always the ICs — the most complex semiconductors — that blow first. So my first troubleshooting step is always to remove them from the circuit and recheck the resistance across power.

The two ICs (a TL074 low-noise quad op-amp and CD4069 hex inverter) weren’t socketed, so I needed to desolder them in order to recheck the circuit with them absent. Rather than use solder braid, I tried out my new hot air pencil that Cort bought for me (and one for himself) in exchange for building him a hotplate (that I need to assemble and deliver).

I turned the pencil up to about 350°C and waved it around the solder side of each IC while rocking an IC puller on the component side. After a little time to warm up the solder, the ICs pulled loose very cleanly.

The hot air pencil scorched the residual flux from the factory assembly,

but after wicking the remaining solder and cleaning the flux, the board looks pretty good. The vicinity of one of the two ICs shows slight damage to the epoxy (?) with the fiber substrate showing through.

Testing with ICs Removed

With the ICs out, the resistance across the power leads was very high, as I would expect it to be.

I soldered in IC sockets and measured again with the ICs reinstalled in the circuit one at a time. The CD4069 was obviously bad and the TL074 was not obviously bad. Joel had a CD4069 on hand; I installed it; and all of the pedal’s logic appeared to work — although I didn’t know yet whether the audio was working properly.

The bad 4069 does have a shiny spot on it. At first I assumed it was flux splash; but I’ve seen melt like that on ICs where the magic smoke had escaped. Maybe the spot really is a symptom of the damage.

Plugging the NiMH battery back in and powering up the pedal, I measured 3.5V across the battery leads, using either the original TL074 op-amp or a TL084 that I had on hand. This still seems like an awful lot of voltage drop for an allegedly 16mA pedal (even given the internal resistance of an aging NiMH battery); but any further diagnosis was going to require more information about symptoms.

Reassembling and Testing

Taking a chance on the TL074 (in part because I didn’t have any on hand), I reassembled the pedal with the original op-amp installed and took it to Jeremy’s house last night for him to try out. (He’s on kind of a wah pedal kick right now, and I’m feeding his habit.)

He grabbed the first power supply he saw, plugged it in, and started playing. It worked, but we had massive 60Hz hum, which didn’t really make sense — why would a fault in the pedal that I hadn’t found and fixed cause that much hum? The power supply section doesn’t have much by way of filtering, the audio section shouldn’t be specifically filtering out 60Hz, and the whole thing shouldn’t be more susceptible to hum than usual because of a broken component.

I suggested that we try a different 9VDC power supply, and went to change it out. Then I found that Jeremy had plugged my 9VAC x0xb0x power supply into my 9VDC Bad Horsie pedal. That’s right, he put 9VAC into the pedal and it still worked, albeit with hum. It was half-wave rectifying AC and that single capacitor filter was enough to get that baby going.

Which means whatever the previous owner did to it involved more than 9VAC — probably quite a bit more (or quite a bit of DC), since the CD4069 is rated for up to 15V supply. I’ll never know — although I really wish I would — exactly what he did to it. Maybe a 24V inkjet printer power supply???

After swapping in the right power supply, the pedal appeared to work correctly — although Jeremy didn’t especially like the sound running his guitar straight into the pedal. I found forum posts agreeing with his opinion that it really needs distortion before the Bad Horsie, which he played with more tonight.

While looking up the pedal’s manual today to find exactly what the controls do, I saw that Morley provides the schematic on their web site. If Jeremy decides that the audio portion of the pedal isn’t working correctly, or if I get too annoyed thinking about how much more current it’s drawing than it’s supposed to, I’ll definitely use the schematic to continue repairing the pedal. Still, this goes to show that one can do a reasonable amount of troubleshooting just by examining the construction and behavior of a circuit without having or using a schematic.

The batteries were due for replacement and the seller removed them to save on shipping costs. I got a UPS with a set of wires and no instructions on how to connect them.

Also one of the wires was compromised … but since it appears to be a ground wire, I figured no big deal if it shorts out against the cage. KIDDING!

Yesterday I figured out the wiring, installed batteries, and got the UPS set up in my server rack.

Batteries

I’ve bought replacement UPS batteries from Digi-Key before, measuring the size I needed and using their parametric search to find sealed lead-acid batteries with the same size and highest capacity. Digi-Key’s replacements for the Liebert UPS seemed a bit pricey this time, though. Using the power of Google, I found a set of replacement batteries from BatterySpec for only $72 plus about $20 shipping.

They processed my order quickly — I ordered after the close of business on a Friday night, they shipped Monday afternoon, and my package was waiting for me Friday when I got home.

At first I thought they had provided fully-insulated battery terminals that I’d have to disassemble to connect the fully-insulated spade terminals on my UPS wiring, but those are just insulating caps for shipping.

Battery Wiring

The first thing I did was repair the ground wire. The wiring harness is a bit odd — it uses two connectors, I assume for current-carrying capacity — but that makes it easy to see how long the ground wire should have been. I stretched everything out and the remaining three wires were all in agreement about how long the cut wire should be.

The original wires are very supple 10-gauge with relatively fine strands. The closest thing I had was stranded 10-gauge left over from an electrical install; it’s not as supple, but it’ll do. I cut it to fit, lap-soldered the connections, and covered them with a double dose of heatshrink tubing.

The next order of business was figuring out how to wire this up, and the wires themselves provided the clues. The two sockets are wired in parallel with each other, so they had to connect at the ends of whatever parallel-series chain the batteries might form. The wires didn’t include any Y cables besides the sockets, so the batteries apparently needed to be connected in a single 48V series chain.

The cage is sized for the batteries to be laid down on edge, but it was easier to figure out the wiring with the batteries standing up. The socketed cables were long enough and had bends in them for the positive connector to reach between the nearest two batteries and the negative connector to reach between the furthest two.

Everything else fell into place like assembling a jigsaw puzzle without looking at the box — the batteries will tip together in pairs with their terminals at opposite edges of the cage, the short wires connect the two end pairs into series chains, and the long wire connects the two chains.

I connected all the wires with the batteries still upright, stopping before the last couple of connections to test carefully with the voltmeter and make sure I hadn’t overlooked anything that was going to short out.

With this much current available, any short circuit would cause a lot of heat very quickly; so knowing I wouldn’t be able to unplug red-hot wires, I had a wirecutter handy in case of extreme emergency. Fortunately it wasn’t needed and everything went together as expected. I measured just over 48V at the sockets from red to black, so all looked well.

I laid the batteries down and tucked the wires away into the grooves at the sides of the cage. I don’t know how it was done originally, but I had to route the black wire through the bottom race and the red through the top in order to be able to close the cage.

All back together and buttoned up.

You can see a nick in a red wire’s insulation, but it doesn’t go through to copper. Because it’s above the Y in the cable, it would have required cutting and resoldering the cable to cover with heatshrink. I didn’t think that was worth the effort, and I don’t put much stock in electrical tape. I guess I could go back and cover it with a larger heatshrink that encloses both of the red wires together.

Reinstalling

The battery cage slid perfectly into the bay.

Connecting it for the first time was a bit unnerving — what if the seller was less than honest and took the UPS out of service because of a severe malfunction? Seeing no evidence of fire or overheating in the battery cage or bay and trusting Liebert to engineer adequate safety systems into their UPS, I took the plunge and connected the cables.

The wires did not immediately get warm. Good so far.

The next order of business (and the next unnerving step) was to plug the UPS into AC power.

Wait …

That’s a 5-20P 20A plug. I don’t have any 5-20R receptacles in my basement.

DRAT.

By fiddling with the pushbuttons on the panel, I somehow got the UPS to turn on while on battery power and the indicator lights looked okay. I had to reference the manual to figure out how to turn it off — press the Standby button twice for about a second each time.

Next Steps

Well, I already want to get an electrician in to run a new service entrance and install a new master breaker box. For now I’ll probably just do something inadvisable with an extension cord.

The seller didn’t include the plastic front bezel, and I’d really like to find one.

PIC Programmer

Trey asks:

Do you have any recommendations regarding a Microchip programmer? There is the PicKit 2 and the Pickit 3. I have read that there are/were issues with the PicKit 3. I know you have used Microchip parts in your designs, but was wondering what your opinion was?

Trey, I’ve never used a PIC that wasn’t already preprogrammed with the LogoChip environment, so I have no experience with PIC programmers.

After reading through PIC and Atmel datasheets in considerable detail to access hardware features on both platforms, my opinion is that I’ll never use a PIC. That’s based on a couple dozen small things that I don’t even remember any more, but which added up to a pretty powerful opinion that Atmel builds a much better thought-out microcontroller that’s much easier to use.

But … that’s not the answer you were looking for. Readers with PIC experience, can you address Trey’s question? Please clearly phrase your responses as statements of opinion (like my opinion above, which is nothing more than an opinion) or as statements of fact with links to supporting information.

Oscilloscope

I am just now starting my journey into electronics and was wondering if you have any recommendations for any particular make/model of oscilloscope?

For someone starting in electronics, before an oscilloscope, I would recommend:

• A $3 multimeter. I’ve started buying a few of these whenever I go to Harbor Freight and find them on sale, and I give them away like candy. Ace Hardware also sometimes has cheap meters in the dump bin.
  
  Is this as accurate as a Fluke? Of course not — but for basic electronics troubleshooting, this is more than adequate. The one useful function it lacks is a beeper for continuity testing — you do have to look up at the screen to read low resistance.
• A breadboard and some components with a list of projects to try. I’d suggest Adafruit’s $50 Arduino budget pack, $65 Arduino starter pack, or $85 Arduino experimentation kit. Even if you’re not that interested in embedded design, the Arduino is a great platform for trying things out and interfacing to the analog electronics, and the Adafruit kits provide a list of experiments to use as a starting point and get the ideas flowing.

But if you’re already doing PIC programming, you seem to be well past the resistors-and-LEDs stage. If you really need a way to visualize signals in order to progress, my oscilloscope recommendation would be whatever working scope you can get for the lowest price, making sure that you do end up with at least one probe (or find a cheap one on eBay).

I paid $25 for an old, used scope about 20 years ago and have only upgraded to a better scope in the last couple of years — which is 20 years old, which I got from a friend of a friend, and which I haven’t put on my bench and started using yet.

The two times I’ve used a different scope are when I found a cheap scope with X-Y inputs that I use for troubleshooting vector arcade game displays, and when I borrowed a digital Tek scope for doing some precise high-frequency measurements.

Granted, I don’t use my scope for calibrating circuits. If you need to do that, you need a better scope, and one that’s calibrated, and that’s going to cost real money. But if visualization is what you’re after, then the cheapest scope that works will do the job.

Planning the Paths

Besides the obvious goal of keeping the wires tidy, my main goal was to position slack in the cables so that the back panel could be lifted out of the case and set to the rear, allowing full access to both circuit boards, without disconnecting anything.

Before doing any real lacing, I mocked up the cable path to make sure everything would work. My first attempt, here, had enough length for the J3 bundle from the lower right of the main board to the right end of the I/O board; but J7’s wires coming from the left edge of the main board looped around too much before heading to the I/O board and didn’t reach their destination.

My second attempt worked much better. I brought J3’s large bundle up in a clockwise loop and all the other connectors’ bundles in an overlapping counterclockwise loop. All the cables reached where they needed to go, all the three-wire cables got tied together into a larger bundle that would hold its shape well, and the two loops flexed well to allow the back panel to be moved back and forth.

Attaching the Cables

I removed all the cables, then started with the longest run, from J7’s connector on the main board to its solder connections on the I/O board. I then used its path as a guide to size J5’s cable to length, soldered in J5’s wires, and tied the two together.

I repeated for J4 and J6, tying up after each to ensure that every successive bundle would follow its intended path and get sized correctly.

After the CCW section was finished, I soldered the J3 bundle to the right end of the I/O board and tied the two bundles together into the overlapping loop.

Since I now had everything attached, I figured I’d test the x0xb0x to make sure it worked before lacing everything into place. It was at this point that I found I couldn’t close the case because of J3’s connector being at the wrong end.

Besides having to desolder J3 at both ends and reattach it, this broke my plan to have the overlapping loops tied together. It wouldn’t do much good to have wires soldered to the I/O board tied to wires soldered to the main board. I could still leave the overlapping loops; I just couldn’t tie them together.

Lacing the Harnesses

After desoldering J3 and setting it aside, I laced the harness that holds everything else. I started at the I/O board, locking and wrapping every time another cable joined or left the bundle and removing my temporary ties along the way. Because of the number of branches, the usual advice of two and a half times as much lacing cord as the length of the main trunk left me short, and I had to run the main cord up to J4-J6 and start a new cord to finish out the run to J7-J5 instead of the other way ’round.

Note that I ended up routing J7 as a short branch off the run to J5 rather than splitting the two in a Y like I mocked up.

I understand that it would be more proper also to tie every bundle of three wires after it splits off the main trunk; but with only about an inch on each after the branch, I’m satisfied with the results.

The harness holds its shape well and it’s easy to see where every three-pin connector is supposed to plug in.

After reattaching the J3 buncle in the proper orientation, I laid out its path and made temporary ties to hold it in position, then started at the main board end and worked toward the I/O board. I finished with the wrap that holds the wires in shape as they fall to the left of the J3 connector on the I/O board.

Again, I’m pleased with how well the J3 harness holds its shape, especially as it doesn’t tie to any points along the way. The two harnesses’ loops overlap nicely in the middle — slightly differently than I had routed them here — and the back panel is very easy to put into and take out of the case.

Adafruit produced x0xb0x kits in batches of 100 as Limor was able to track down enough “rare parts,” order circuit boards, and assemble the common parts into kits. I’d been on her waiting list since 2008, so was terribly disappointed when she officially announced what we had all come to realize anyway — that tracking down the rare parts was becoming enough of a hassle, she wasn’t having any fun doing it and wasn’t going to produce any more kits.

Happily, Limor announced shortly thereafter that thanks to Adafruit’s open-source hardware license, James Wilsey of Willzyx Music in Taiwan has taken up the torch and would shortly be offering x0xb0x kits.

I browsed the Willzyx web site and saw an Express Kit with rare parts, circuit boards, and panels, but no case and common parts. I emailed James to thank him for making the kits available and ask whether he’d be producing full kits. He replied that he would shortly; and in spite of having a no-preorder policy, offered to hold one for me as soon as they were ready if I was interested.

I said yes, he soon told me that the kit was ready (even though the updated instructions weren’t yet), I sent payment, and he sent my kit, very nicely packed and with quick shipping and international tracking. James has been an absolute pleasure to deal with, pre-, mid-, and post-order.

What follows are a few notes from the build — not a time-lapse of everything all the way through, but things that struck me as unusual or interesting. All mistakes I made were my own fault for not waiting for the updated instructions.

Testing Each Stage

I’m just a bit too young to have assembled a Heathkit, so Adafruit’s instructions for the first several stages were novel to me — she identifies a section to assemble, then stops to have you test what you’ve just built. The power supply section, for example, includes notes for testing AC voltage and regulated DC voltage at two different points. Modular testing is a great way to make sure you don’t spend 40 hours putting your kit together and then have no idea why it doesn’t work.

Willzyx, by the way, provides sockets for all the ICs (which I hadn’t noticed when I soldered the op-amp above) and nice connectors for the inter-board jumpers (which I hadn’t noticed when I provided my own). Using his instructions will be much easier than desoldering these parts later.

Diffusing the LEDs

The kit includes high-brightness, non-diffused red LEDs. I don’t like the look of non-diffused LEDs, especially as panel indicators, because their low viewing angle makes them hard to see unless you’re looking at them dead-on (at which point they’re too bright). So I used my technique from four years ago (when I had just started the blog) and frosted them.

The diffused LEDs are noticeably translucent instead of water-clear like the unmodified originals.

And they provide a nice, even illumination across wide viewing angles. (Note that they’re really quite red when you look at them with anything other than this camera.)

Once I had all the LEDs prepared, to solder them with proper alignment to fit the front panel, I inserted them in their standoffs and did the old trick of tack-solder one leg, then adjust the LED while reheating the joint. Then I put the front panel over the LEDs (further on than it actually fits in final assembly) to hold them all securely in position while soldering the cathodes and resoldering the anodes.

J3 Plug Goes on the I/O Board

I had the x0xb0x nearly completed and ready to install all the cable bundles when I noticed that Willzyx provided wiring harnesses with a mating connector at one end to make servicing the x0xb0x easier. (The original kit just provided ribbon cables to solder at both ends.) Even after emailing James to confirm which board each plug was supposed to go on, I got this one wrong.

And when you get it wrong, the case doesn’t close. This is at the narrow front end of the case, and the connector is too tall. This was a nuisance to desolder and redo — but I ended up with tidier wiring the second time around, so it wasn’t all bad.

Shorten the Rotary Switch Shafts

The original Adafruit pre-assembly preparation instructions say to cut all the potentiometer shafts to the same length. Willzyx provides potentiometers that already have same-sized shafts (thank you!!!), so I disregarded this instruction — at my own peril.

Yeah, the potentiometers all have same-sized shafts, but the two rotary switches have shafts way too long for the knobs to reach the ground. These would have been much easier to cut before installing. Just another case where the updated instructions will solve the problem for everyone else, and I should have looked at the parts more carefully since I knew I was building without up-to-date information.

Note that the flats on the shafts (which I refiled for the knobs’ set screws) are opposite the selected function. I powered it up to double-check before filing.

Done!

After two weekends of intermittent work, it’s done and 100% functional. I’ve been having fun this afternoon tweaking knobs to the bass line of “Sweet Emotion,” the most interesting one-bar pattern that I had stuck in my head. Thanks, Limor Fried and James Wilsey!

• Capture a short sample of a MIDI performance, including key velocity data.
• Quantize to a tempo set by a “tap tempo” pedal continually and dynamically throughout the capture, rather than to an LED or click track.
• Loop and play back, by default to the last tempo seen but honoring continuous “tap tempo” data from the same pedal.

Using a MIDI sequencer with these “tap tempo” features should give greater flexibility for capture and playback during a live ensemble performance than using a traditional audio looper, which requires the whole ensemble to play to the tempo recorded in the loop.

But my real motivation is to be able to play a pattern and then make gradual, multi-bar changes to the analog character of the sound without having to continue playing with one hand and turn knobs with the other.

Record a one-bar pattern on a MIDI keyboard driving a x0xb0x (or a real TB-303, if you’re filthy rich enough to have one and a DIN-sync MIDI adapter to go with it), then play it back and slowly tweak the knobs while everyone else jams on for a bit.

Am I going to find that all of this functionality already exists within the x0xb0x? (It looks like it might be close — MIDI ports; internal sequencer; variable tempo, although perhaps not that sophisticated.) Alternatively, are there MIDI sequencers that do all of this? Is this de rigeuer for every sequencer under the sun?

I’ve always been curious about the construction quality of commercial patch cords — just how good are the connections buried under those lovely molded jackets and strain reliefs?

Naturally, the faulty end was the last one I disassembled. (Logic joke!)

A failure rate of one in twenty-fivish (I have three bundles of patch cords) is quite a bit higher than I expected, especially as the fault was a solder joint broken clear off of the center pin.

Notice how little of the braided shield wire remains. This doesn’t speak well to the overall quality and reliability of the patch cords — even though this part of the wire is cast inside the rubber housing and can’t flex.

Note also that the cable has two signal wires. The manufacturer apparently uses the same cable for TS (tip-shield, for unbalanced signals) patch cords as they do for TRS (tip-ring-shield, for balanced signals) patch cords. (The same bulk cable could be used for stereo unbalanced transmission — although I’d prefer to see each signal wire individually coaxially shielded.)

At this point, my curiosity shifted to whether I could fix up the cable and put it back together in a way that I found aesthetically acceptable.

When I mounted the plug to desolder the braid so I could strip back the jacket and start with fresh sections of copper, I noticed that the solder was very grey. I suspect it’s lead-free and I suspect that the greater challenges of lead-free solder contributed to the broken solder joint.

I reformed and tinned the shield wire and stripped and tinned the tip wires. I also tinned the shield and pin so the joints would go together well — which they did. And I tested for continuity and shorts after soldering, to be sure of my rework.

I slipped the broken pieces of insulating plastic back between the wires so the shield wires wouldn’t short out onto the pins. I then carved out the interior of the molded jackets, since I wasn’t going to be able to realign the insulation and wires exactly with the recesses from when the housings were originally formed.

After test-fitting and carving out more of the molded covers a few times, I got a fit I was happy with. I put the covers back on and sealed the deal with heat-shrink, which did an admirable job of conforming to the shape and texture of the original molding.

Making the repair was never an economic decision; but having fixed the patch cord, I may as well use it.

Who Made It?

I could never find a manufacturer’s logo on the patch cord or molded ends, nor does the cord look identical to the current catalog entry for the patch cord bundle I think it is. I’ll avoid buying anything more from the brand I suspect; but because I’m not certain of it, I’m not comfortable mentioning it here.

It’d make an interesting demonstration to buy a couple of packages each of several manufacturers’ patch cords and dissassemble and inspect them like this, to assess the build quality. Maybe a musicians magazine has already done that review?

Saturday night the EasyBright already got its public debut! I played a pair of classic rock concerts Friday and Saturday nights, and Friday had trouble seeing my music (occasionally folded out to four pages) with the clip-on stand light I was using. Saturday after assembling the EasyBright, I built an LED “wand” music stand light that worked marvelously.

I didn’t have a lot of time for construction, so I cut a 1/2″ dowel to 3′ length and drilled eighteen 1/8″ holes through it (axially, not longitudinally) every 2″. Paint wouldn’t dry before the show, so I sanded the dowel and then colored it with a permanent marker. I then installed bright flat-top LEDs with a good viewing angle into the holes and bent the leads out in opposite directions.

I lap-soldered teflon-insulated (heat-resistant) wire from LED to LED with heat-shrink tubing preinstalled — but didn’t shrink the tubing until after I had tested the LEDs, in case I needed to repair any solder joints. I skipped LEDs to make an A-B-C-A-B-C pattern so if a chain failed, I’d lose light evenly along the whole wand instead of all in one section.

I crimped connectors onto the wires, connected everything to the EasyBright, put an appropriate connector on a 24VDC wall wart, and fired it up perfectly on the first try. (Such luck!) I disconnected the wand, reseated and shrank the heat-shrink, zip-tied the wires in place, and then powered up the wand to burn in for an hour before leaving home for the concert.

On stage, it delivered a very even wash of illumination across my music, giving me a great view all through the show.

The circuit board is so lightweight, it was comfortably suspended in mid-air between the keyboard rack and my music stand by the power and LED wires. For the long term, I’m trying to decide whether how it should be mounted to the wand — perhaps attached near the end inside a sleeve of giant heat-shrink.

At the end of March, I broke my MakerBot CupCake idler wheel while trying out my new filament drive worm-pulley. In April, my friends Scott Smith and Ben Wynne in San Diego machined me some aluminum replacement wheels, which are totally awesome.

Old and busted; new hotness. Yeah, baby!

This wheel press-fits perfectly onto the bearing, starting by hand and then leaning heavily on it on a countertop. It’s thicker than the original wheel, making precise alignment with the drive pulley less important. It even has a knurled edge — showoffs!

I’d been experiencing “plaid” printing, in which the filament feed rate dropped at very regular intervals, and attributed it to the (tangible) irregularities of the acrylic idler wheel. But I’m still getting plaid prints, and I don’t think my aluminum wheel (hot off the lathe) is irregular, so the problem must be elsewhere.

Hm, look at the deflection of my filament feed motor shaft, all the way to the left of the hole in the enclosure.

Hm, look at the deflection of the shaft now, when the flat hits the edge. That would explain why the weak feed is so regular — recovery doesn’t rely on the drive pulley maybe grabbing the filament and maybe being able to spin the idler wheel to a different spot before it gets going again.

Looks like I need a bearing on that motor shaft. I printed a shoulder washer/bushing for it and it helped for a while, but not enough. I think a real, metal bearing is in my future. And perhaps a different drive geometry. A lot of good filament feed designs are being uploaded to Thingiverse.

Last week while watching Mannequin (a very young and fresh Kim Cattrall, a goofy plot, and music by Starship — what could be better? okay, if it had John Cusack and were set in Shermer, Illinois, yes, that would be better) I split all the EasyBright components into a parts bin for easy access and portability.

Saturday afternoon I put together the first sample.

This is waaaaaay too much solder paste for 0603 parts and 1/40″ IC pin spacing. I had to remove several solder bridges from the IC, and the passives had solder mounds instead of fillets. I took the picture specifically to record how much paste I used so I could adjust on the second attempt.

Here’s the cleaned-up board, front side.

Back side, with hand-written labels for the current rating and the serial number (S00). The “permanent” marker comes off easily with rubbing alcohol — I need to get some clear nail polish to seal it in.

Changes

Even before assembly, I had made notes about (and started implementing) things to fix whenever I print the next boards:

• Change the IC’s ground connection from a via outside the IC footprint to a trace going straight in to the heatsink pad. I had routed that connection before I confirmed with Maxim that the pad is okay to connect to ground — it’s just not okay to be the only ground — and then forgot to go back and change it. Removing that via gives me a little more room to route the bottom-side LED power traces cleanly, and also:
• Increase the pad size on the optional through-hole current-sense resistors. This, believe it or not, is EAGLE’s default pad size, and I think it’d be challenging to solder without a good, narrow-tipped iron.
• Increase the trace isolation on the solder-side ground pour. There’s no reason to have it that close to the pads.
• More subtle, I spaced the 2-pin connector pads an extra .02″ apart to see whether I could get the connectors to friction-fit for ease while soldering. They don’t quite. Either change the library footprint to space the pads a little further apart or just get used to pinching the leads together before stuffing the parts and soldering, which works better than I had expected.

I’m still delighted!