Repairing a Bad Horsie 2 Wah Pedal with Power Damage

July 7th, 2010

Bad Horsie 2 wah pedal

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.

Bad Horsie 2 wah pedal circuit board

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.

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Installing Batteries in a Liebert GXT2-2000RT120 UPS

June 27th, 2010

A while back, I bought a secondhand Liebert GXT2-2000RT120 uninterruptible power supply (UPS) on eBay. The GXT2 is a series of online UPSes, meaning that the output power always comes from the inverters off the battery bank; it doesn’t switch from utility power to battery power like an offline UPS. Besides eliminating any possible switchover glitches, online UPSes always deliver conditioned power at a constant voltage. The 2000RT120 is a 2000VA unit with 120V output — large enough to power all my servers for a good little while.

Liebert GXT2-2000RT120 UPS with battery cage disassembled

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.

Liebert GXT2-2000RT120 UPS battery wiring

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.

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Q&A: PIC Programmer, Oscilloscope

June 19th, 2010

I get very specific questions via my contact form, but also questions about more general issues that might be of interest to a larger audience. I’m going to start posting the latter category here.

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.

Lacing the x0xb0x Wiring Harnesses

June 6th, 2010

This isn’t part of a normal x0xb0x build so I didn’t throw it into my build notes, but I had fun figuring out how to route and lace the x0xb0x’s wiring harnesses. I know lacing is overkill for this; but without some kind of cable management, the individual wires of each cable wouldn’t even stay together. Had the kit included ribbon cables, I wouldn’t have bothered.

Planning the Paths

First pass at x0xb0x cable routing

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.

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Building the x0xb0x

June 6th, 2010

As I noted previously, I recently got a x0xb0x kit. The x0xb0x is an open-source-hardware replica of the 1980s Roland TB-303 bassline synthesizer (and sequencer) that was influential in the development of acid house music. Limor of Adafruit Industries and a mysterious, anonymous German studied the TB-303 schematics and measured the behavior of its now-rare semiconductors and designed a replica with the same analog circuitry and new digital features, including MIDI I/O (supplementing Roland’s pre-MIDI “DIN sync”) and simpler sequencer programming.

Assembled x0xb0x, top view

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.

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MIDI Looper?

May 31st, 2010

I’m starting to think I’d like a MIDI sequencer that behaves somewhat like a looper, doing the following:

  • 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?

Repairing a Patch Cord

May 31st, 2010

Recently a couple of pieces of audio processing equipment I’ve bought used have had bad left channels. After recognizing the pattern, I finally thought to swap out the patch cord I had left plugged into the “test” channel on my keyboard mixer, and voila! Left channels fixed.

Audio patch cord, disassembled

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!)

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EasyBright on Stage

May 25th, 2010

Music stand wand light with lens flare

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.

End of LED wand music stand light

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.

Wiring on LED wand music stand light

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.

Connectors at end of LED wand music stand light

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.

LED wand music stand light

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

EasyBright circuit board driving LED wand music stand light

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.

MakerBot CupCake Aluminum Idler Wheel and Printing in Plaid Due to Motor Shaft Deflection

May 25th, 2010

Aluminum idler wheels for MakerBot CupCake

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.

Broken acrylic and replacement aluminum MakerBot CupCake Plastruder idler wheels

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!

Plaid print from MakerBot CupCake

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.

MakerBot CupCake filament feed

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

MakerBot CupCake filament feed

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.

Assembling the first EasyBright

May 25th, 2010

EasyBright components

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.

EasyBright-3L constant-current LED string driver PCB with solder paste

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.

EasyBright-3L constant-current LED string driver, front

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

EasyBright-3L constant-current LED string driver, back

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!