Archive for the ‘Hacks’ Category

Modifying a Harbor Freight Solar Charger

Tuesday, June 21st, 2011

My dashboard solar charger is one of the more useful things I’ve bought from Harbor Freight. My van has some weak short-circuit and slowly drains the battery, and as I don’t use the van all that often, I was at risk of coming out to a completely drained battery. I now keep one of these on the dash and the battery is always topped off. When I first connected it, the van was sitting in shade and the (old) automotive battery measured 5V (!); after a week it was up to 9V and after another week it was fully charged. Now I don’t ever have to think about a drained battery again. At about $20 list and $15 on sale, it’s a steal.

Harbor Freight solar charger model 44768

The bus conversion project is languishing but not forgotten, and I’ve been wanting to put one of these chargers into the bus for the same reasons as I had for the van. The wiring situation is a little different, though — the bus has no cigarette lighter / power port, I’m intending to wire 12VDC throughout the bus with Anderson power pole connectors, and I might like to have multiple solar trickle chargers (even before I install larger solar panels on the roof).

The issue with multiple panels, and even with a single panel connected to a battery that will also be charged by the alternator, and even with a single panel that may still be connected to the battery at night, is that photovoltaic cells don’t like to have reverse voltage applied. The photovoltaic effect happens in a semiconductor junction, and although I can no longer find the reference I was reading the other day, I still know the cell doesn’t do well with a reverse voltage and should really be diode-protected.

Because I wasn’t sure how much (if any) circuitry was in the panel and how much (if any) was in the automotive power plug connector, I had to take both apart to (A) make sure the panel would be diode-protected even after I chopped off the power plug and (B) see whether either held any relevant / useful circuitry.

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Modifying a Car USB Adapter to (Finally) Charge My Cell Phone

Saturday, May 28th, 2011

A couple of years ago, I received this automotive USB-connector power adapter as a promotion at a conference. I use it to keep my iPod nano charged in the car, but I’ve noticed it doesn’t charge my Blackberry well. To be precise, it doesn’t charge my Blackberry. In fact, I’ve never been clear whether it even slows the rate of discharge, and sometimes it seems like it speeds it. The Blackberry shows the lightning bolt charging symbol (The charging symbol is a lightning bolt, srsly? Ben Franklin is personally charging my phone?) but nobody’s home.

Note that I don’t blame the vendor whose logo happens to be on it — I’m sure they didn’t manufacture it.

Automotive USB power adapter

After driving two and a half hours a week ago starting with a half charge on my BlackBerry, plugging it in midway through the trip, and arriving to have the BlackBerry finally shut off its radio due to depleted charge; and due to being in the presence of Cort; I decided it was time to see why the adapter couldn’t provide enough charge for the BlackBerry.

Inside the Power Adapter

Sample step-down circuit using RT34063APS DC-DC converter

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Guest Post: LEDs and Ping-Pong Balls to Replace 10W Sign Bulbs

Friday, March 25th, 2011

My friend Cort Buffington doesn’t have an active blog of his own but is doing interesting things with 110VAC light bulbs and is looking for ways to migrate to LEDs.

Star Seq'r and disco ball

What follows is a write-up of his tests with LEDs and ping-pong-ball diffusers.

Cort’s Quest for 10W Sign Bulb Replacements

For some time I’ve been trying to figure out how to make an LED equivalent to a 10W colored sign bulb. Whether it be the G style intermediate base or the S style medium base. The big problem has been a diffuser. Sign bulbs are meant to be looked at, not to illuminate other things, so this is of paramount importance. I very quickly came across a LOT of information online with folks using ping pong balls, and Keith was just as eager as I to try this out. The initial tests with ping pong balls worked…. sort of. Ping pong (or beer pong if you’re in college) balls do work, but there are a couple of immediate problems:

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PCB Milling with the MakerBot CupCake: Aluminum Leveling Platform

Saturday, March 19th, 2011

Last weekend I got my Dremel rigidly mounted in my CupCake for PCB milling, but the platform holding the PCB was attached with double-stick foam and was being deflected by the milling bit cutting the copper, causing considerable deviation from the intended milling path.

Leveling platform in MakerBot CupCake

Last night Steve cut some more aluminum plate for me and today I assembled a rigidly-mounted leveling platform to replace the stock build platform. The lower plate has holes matching the machine screws attaching the top of the Y stage, and I used slightly longer screws to bolt through both the aluminum plate and the original wood top into the Y carriage.

Leveling screw with nylock nut, upper view

I drilled holes in the corners, tapped the upper plate, and enlarged the holes in the lower plate. The socket-head cap screws spin freely in the lower plate while adjusting the upper plate’s height (I used a continuity meter to check when the milling bit was just barely touching the plate in each corner); then the nylon-insert nuts lock the screws in position. The whole assembly is quite rigid once tightened.

A number of designs for leveling build platforms use only springs between the two plates. I was concerned that without a nut, the machine screws might back out under vibration. Also, when extruding, having a platform with some give reduces the damage if you miscalculate the Z position and gouge the platform; but for milling, the whole point of this replacement is to remove any play in the platform.

PCB milled in MakerBot CupCake

The results were not tremendously better than before (left board, top row of pads; right board from commercial mill for comparison), so I slowed the feed rate to .1″ per minute and let the mill finish the rest of the board for five hours, just to see whether I could produce usable traces. The traces cut at an outrageously slow feed rate are much better than previous results, but still a bit, shall we say, interpretive for my taste.

Having watched the Dremel bit trying to cut the copper and having tested it handheld out of the machine, I do recognize that it’s not the right bit for this job. I have some carbide engraving bits recommended by Pierre (exuinoxefr) on the way from Hong Kong, and I think they’ll make a significant difference. In April.

Meanwhile, note the three pads in the center of the board. Even at only one stepper motor step per second, the board took a very consistently incorrect path under the toolhead. Also note that the diagonal lines look like they were drawn with a left-handed quill pen — NE/SW lines are thicker than NW/SE.

I believe this is caused by the considerable play between the original CupCake bushings and the guide rods. Tighter bushings would cause more friction, so they were chosen for a bit of a loose fit. Even though the platform is now rigidly mounted on the Y carriage, the Y carriage wiggles on the Y guide rods and the X-Y carriage wiggles on the X guide rods.

I’m extremely interested in the Mendel-inspired replacement X-Y assembly by Thingiverse contributor “twotimes.” It replaces the bushings with sets of roller bearings spaced around the guide rods; the bearings can be tightened against the rods and still roll smoothly. I intend to get in touch and ask whether it successfully removes the play from the carriages.

Leveling platform in MakerBot CupCake, closeup

Although my immediate interest is whether I can use the CupCake that I already own as a PCB milling machine, the enhancements I’m making will improve it as a filament deposition machine as well. The lack of leveling in my heated build platform prevented me from printing larger models; I’ve already drilled my heated platform to fit interchangeably into this new system. Smoother X-Y action from a replacement carriage can only help, too.

PCB Milling with the MakerBot CupCake: Aluminum Z-Stage Supplement for Rigid Dremel Mounting

Sunday, March 13th, 2011

In my previous attempt to trace-isolation-mill a PCB with my MakerBot CupCake, the CupCake’s entire acrylic Z platform (intended to support the light weight of the filament heater and extruder) was flexing under the torque of the Dremel bit dragging through the copper layer of the PCB.

MakerBot CupCake with aluminum Z-stage reinforcement and Dremel mount

This week I picked up 1/4″ aluminum plate at the yard to reinforce the Z stage and support a more rigid Dremel mount. Steve Atwood printed the DXF of the MakerBot Z stage mechanical drawing for me, which I used as a template to drill and tap holes matching those in the acrylic (forgetting, unfortunately, to double-check the accuracy of the feed rate on Steve’s inkjet printer — but I compensated for the resulting aspect ratio problem with a file).

MakerBot CupCake with aluminum Z-stage reinforcement and Dremel mounted

I put together a good-enough Dremel mount with plastic from the visual arts scrap bin. Initially I lined the mounting hole with foam weatherstripping, but the Dremel was wiggling just a bit even with the clamp tightened down. It’s less wiggly without the foam.

Circuit board milled on MakerBot CupCake

The multi-pass milling looks like someone applied a GIMP randomizing filter to the original pattern, but at least the bit is consistently cutting the copper. The Dremel mount isn’t flexing any more — the irregularity is from the double-stick foam I used to attach the milling platform to the XY stage; the platform and board were swaying significantly under the bit.

PCB Milling with the MakerBot CupCake and a Dremel (Almost)

Monday, March 7th, 2011

Dremel mounted in MakerBot CupCake (lower view)

My Dremel’s spindle had much more solid bearings than the Handy Grinder, so I mounted it in the CupCake tonight to try milling with it.

Dremel mounted in MakerBot CupCake (upper view)

It fit even worse through the Z stage than the Handy Grinder, but I remember having said something about the drill not even needing to be vertical as long as the bit’s tip made contact with the workpiece.

Dremel milling PCB in MakerBot CupCake

The XY platform wasn’t quite level (deeper cutting on the right than the left); but the real problem was that the Z stage was flexing. Not lifting off the Z stage guides — I could feel the acrylic bending as the tool direction changed. This demanded backing off the Z axis to an extremely shallow, ineffective cut to keep the milling tip from tracking the cutting direction as it did with the Handy Grinder.

Increasing the rigidity of the Z stage by bolting a large plate to it while mounting the Dremel is my top priority for getting closer to usable performance.

PCB after milling attempts

Straight off the mill after a variety of different attempts on the same workpiece. Parts of it almost look usable …

PCB after milling attempts, sanded

But sanded, it’s clear that in most places the bit barely scratched the copper and wasn’t even close to scoring through, because of the obligatory shallow cut.

PCB Milling with the MakerBot CupCake (Almost)

Sunday, March 6th, 2011

I crave a CNC mill for trace-isolation milling prototype PC boards and I haven’t managed to get my CupCake filament deposition machine calibrated so I can use it. (Build platform leveling and filament feed are my current showstoppers. I’ll get back to it.)

I knew that someone had proposed mounting a Dremel in place of the CupCake’s extruder and that MaskedRetriever had modeled a mounting bracket; but curiously, I haven’t heard any more about using the CupCake for milling. Surely someone has done it; I just haven’t run across it.

Last night while I was asleep, the facts and the immediacy of the situation came together: EAGLE can output trace-isolation g-code and ReplicatorG reads g-code and drives the CupCake. Really??? PCB trace-isolation milling is that simple???

Yes. Yes it is.

Circuit board layout drawn with pen in MakerBot CupCake

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Temperature Deviation Alarm Board for PID Crockpot Controller

Friday, February 11th, 2011

After assembling my PID crockpot controller, I successfully cooked a couple of medium KC strips at 60°C. When I tried to cook medium-rare at 55°C, though, I kept finding the temperature at 59°C. Not believing that I’m destined to eat medium steaks for the rest of my life, I want to fix this.

My first guess about what’s happening is that the crockpot is well-enough insulated that the controller’s longest delay for how often it turns on the heat is still too short. If so, I may get better control using the crockpot on its (dumb) low heat setting, which could be activated more frequently without driving the temperature as high.

PID crockpot controller with temperature deviation alarm LEDs

Regardless, if I can’t trust the controller to control, I need a monitor external to the controller to let me know when the temperature has gone out of range so I know I don’t yet have a satisfactory system. Although the immediate problem was overheating, I should also like to know about undertemperature problems as well. Happily, the controller has temperature deviation alarms; but less happily, they are momentary and only show when the temperature is currently out of range. Enter the alarm latch.

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Low-Temperature-Cooked-Eggs in a PID-Controlled Crockpot

Tuesday, December 14th, 2010

The web is ablaze with projects for sous-vide (vacuum-sealed) and low-temperature / long-duration cooking. For those not familiar, the basic idea is that if a perfectly-cooked medium-rare steak is 120°F / 49°C in the center, by cooking traditionally on a grill, you overcook it everywhere but the center. Instead of cooking at a higher temperature and waiting exactly the right amount of time for the inside to warm up to the desired temperature, cook the entire piece in a water bath at the desired final temperature for a long time, then sear the outside to make it extra yummy.

PID-controlled crockpot cooking two eggs

My project this weekend, rolling around in my head for way too long and finally kicked into motion by EMSL’s omelette-in-the-shell post, is nothing new nor revolutionary; it’s merely mine. Like many others before me, I plugged a crockpot into a PID controller to turn the crockpot’s heating element on and off and maintain its temperature precisely over a long period of time.

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Making Mini Extension Cords / Testing New Solder and Heatshrink Techniques

Sunday, March 7th, 2010

When you cut up an extension cord for speaker cable (I’m no golden-eared audiophile; I just need some copper to get a few hundred watts from place to place), save the ends to reassemble into mini extension cords. They’re perfect for plugging wall warts into receps and power strips without making adjacent receps unusable too.

I’ve spliced a lot of different kinds of cables — sometimes repairs for friends, sometimes Frankensteining things together for a project — and I’ve always been dissatisfied with the aesthetics when I’m done. Covering the joint in heatshrink hides the ugly splices from direct view, but the heatshrink tapers where it falls off the edge of the cable’s jackets and has unsightly bumps covering the solder joints.

This weekend I tried out a couple of ideas for achieving a smoother splice. The basic method was sound; and although the results aren’t yet what I hope to accomplish, I think they’re leading in the right direction.

Extension cord with jacket ends cut for splicing

My first idea was based on a woodworking scarf joint — a fancy term for cutting ends on a diagonal to make a joint less visible. I sliced each jacket lengthwise about an inch and a half from the cut end, then attempted to cut the peeled jackets into smooth diagonals.

Offset solder joints in a cable splice

I tied the jacket pieces out of the way with velcro, preloaded the wires with heatshrink to cover the splices, and soldered the individual wires together. Note that the individual joints are all offset so that even if the heatshrink were to fail or be abraded, the exposed joints still couldn’t come into contact and short out.

Cable splice with jacket pieces not quite fitting

It turns out that eyeballing the mating jacket shapes before putting the cable back together is a bad idea (or at least that I’m not very good at it). I left a fair bit of gap, uh, everywhere — if I were to try it again, I’d wait to cut the scarf (scarves?) until the reassembly stage, at which point I could do a better job of mating them.

Note that the way the jackets flare out where they come from the unaltered cables into the joint is due to heat while heatshrinking the individual wires, not due to the bulk of the splice area.

Spliced cable with lumpy heatshrink

The result is arguably smoother than my previous methods; but because the lumps don’t logically derive from the splices inside, I actually find it more aesthetically displeasing.

Spliced cable with jacket rewrapped over joint

On the second cord I spliced, I slit the left jacket but didn’t shape the split end and I cut the right jacket completely off the cable. After soldering and heatshrinking the wires, I wrapped the left jacket back around the joint, covering it pretty cleanly. The gap where the two ends’ jackets meet is quite evident, but this shows that rewrapping the wires in the cables’ own jacket is a considerable improvement over just heatshrinking the joint.

Two spliced extension cords

Two short cords, ready to use with wall warts.

For next time, I’m most interested in retrying the scarf joint and cutting the two jackets to mate after finishing splice. I think it offers a good chance of minimizing the gap at the end of each jacket, and I think the long diagonal gap under the heatshrink could be nearly invisible with a little care.

Obligatory cautions: Electricity is dangerous. Splicing cords is a bad idea. Don’t burn your house down. Make sure extension cords are unplugged before soldering. Do not taunt mini extension cords.