Monitoring Battery Voltage

February 12th, 2011 by Keith Neufeld

Battery and voltage regulator schematic

Hey, real EE types out there, is there any reason I can’t monitor 12V battery voltage using a simple voltage divider into an A/D input of a microcontroller that’s powered by a voltage regulator on that same battery?

This seems straightforward, but I ask because there seem to be a lot of fancy circuits and devices out there for monitoring supply voltage. It seems to me they all revolve around monitoring the device’s own VCC and where to get a reliable AREF when you don’t trust your own supply.

In the case of monitoring a battery voltage that will always be much higher than the dropout of the voltage regulator powering the microcontroller which generates its own AREF, I can’t think of any reason to get fancier than this.

I would Just Do It but I don’t have a good test setup for this and I’m getting ready to commit it to a board layout.

Water and Electronics

February 11th, 2011 by Keith Neufeld

Three days after we upgrade an ancient switch in the campus golf course headquarters, a supply pipe breaks overhead and pours water into our new switch. It’s “environmentally hardened,” but that doesn’t seem to cover immersion.

As a state university, we’re self-insured and there’s no way we’re getting a T&M refurb from the vendor on water damage, no matter how generous they may be. So I’m getting nothing for this dead switch and I may as well see whether there’s any hope of cleaning it.

Cisco 2940 switch interior after water damage

Oh. Nope, not really.

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Temperature Deviation Alarm Board for PID Crockpot Controller

February 11th, 2011 by Keith Neufeld

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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Cleaned It. What Now?

January 28th, 2011 by Keith Neufeld

Rotary crank telephone, dirty

People bring me the most wonderful things!

Rotary crank telephone, cleaned

Anyone have a favorite plastic polish?

Old telephone handset

I suppose I should build a VoIP phone system and get an analog terminal adapter, eh?

Does Used Tinnit Ever Work?

January 21st, 2011 by Keith Neufeld

The board being too long for my Pyrex dish and the overlap in the middle notwithstanding, this dull, mottled finish is typical of what I get every time I use TInnit other than the day I mix it.

PC board after tinning in used Tinnit

The precipitate never re-dissolves; and I’m guessing that the salts sitting directly on the board are what cause the mottling.

I find this curious, as I mixed this batch only two weeks ago, when it worked noticeably better than this … although now that I mention it, I think even then it produced duller results than it has in the past. Perhaps I exceeded the shelf life of the unopened package, so perhaps I’m being unduly hard on the Tinnit; but I’ve had the same problem before.

PC board after tinning in Tinnit and wet-sanding

I’ve been having good luck lately with scouring pads to shine up the boards; but tonight I had to resort to wet-sanding. Turned out fairly well.

No, that’s not how I typically lay out circuit boards.

Yes, I’ll be posting a lot more about what I’ve been doing for the last month as soon as Steve and I get his sculpture delivered to the gallery before 17:00 tomorrow.

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

December 14th, 2010 by Keith Neufeld

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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Thomas Jefferson on Open-Source

December 8th, 2010 by Keith Neufeld

Why have I never before seen this quote, cited (as I find on Google) by a wide variety of highly reputed maker-friendly organizations?

He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me.

Found in an interview with Sanjoy Mahajan, author of Street-Fighting Mathematics: The Art of Educated Guessing and Opportunistic Problem Solving, on the Freakonomics blog.

Visiting San Diego

October 14th, 2010 by Keith Neufeld

I’ve been in Anaheim, California for a conference this week, and I had the happy opportunity over the weekend to drive down to San Diego and meet in real life a couple of long-time blog friends, Scott and Ben.

Keith's Restaurant sign

I knew I was in the right place as soon as I looked out my hotel window.

Scott Smith's laser cutter frame

Scott is building a copy of bdring’s DIY laser cutter, which looks fantastic. Over the weekend Scott was assembling the sleds that transport the mirror over the workpiece. It’s a very nice design — everything is modular and everything is adjustable.

Fly-milled delrin and aluminum

Scott and his machining mentor Peter generously demonstrated milling techniques on Scott’s Sherline mill. Shown is a fly cutter that was just used to smooth the surface of delrin and aluminum blocks. Although it’s not mirror-shiny, I was impressed at how easy it is (with the right cutting and feed rates) to clean up a face. Peter also demonstrated the use of an edge-finder to precisely position a hole drilled into the edge of an acrylic plate for the laser cutter.

Scott Smith's CNC mill interface

Scott’s mill came CNC-ready with mounts for stepper motors on all of the axes. Scott designed and built his own interface between the PC’s parallel port and the stepper controls, adding indicator lights and the all-important stop button.

Lemons on tree

California is full of things I’ve never seen before, like lemons on trees

Ben Wynne soldering an EasyBright

and people other than me

Scott Smith soldering an EasyBright

soldering together EasyBrights. I don’t have the microscope, though, so I don’t have to make the squinty face.

Ben Wynne's RepRap Mendel

Scott and Ben have both been interested in my progress (and lack of usable results) on my MakerBot CupCake and Ben had just finished assembling a RepRap Mendel when I arrived. It’s much more interesting in person than any picture or video I’ve seen has captured. Compared to the CupCake, it’s incredibly smooth, quiet, precise, and easy to calibrate. On day two, Ben was already churning out prints I envied.

Between Scott’s mill, Ben’s RepRap, and Scott’s laser cutter, they’re set to prototype just about anything. I did suggest that Scott should build a water-jet cutter next, but he wasn’t having any of that. I may need some time to warm him up to the idea.

Project boxes at Fry's Electronics

We paid a visit to Fry’s Electronics, a legendary California electronics components and computer retailer. Although they’ve transformed into primarily a big-box electronics store, I was still impressed with their hobbyist / components section, including a larger variety of project boxes than I’d seen in one place and a good selection of components, including SMT passives, right there on the rack for the buying.

Min Smith playing guqin

Back at Scott’s house, his wife Min was practicing her guqin, a Chinese instrument you may remember from a Jet Li movie. Having been raised listening almost exclusively to western music (“We have both kinds!” — no, not that western music), I found its tuning even more unfamiliar than that of the guitar — it’s not tuned in regular intervals.

Sunset over the Pacific

To top it all off, we had time to wander down to the beach for a California sunset. Thanks, Scott, for an excellent visit with good electronics, great food, and local sights!

Fixing Jeremy’s Ford Mach 460 Bass Amplifier

October 2nd, 2010 by Keith Neufeld

Sometimes you get lucky.

Ford Mach 460 bass amplifier

My friend Jeremy has a 1995 Mustang that had the factory premium sound system in it when he bought the car used. The CD player was broken and he had the head unit replaced within a couple of weeks of owning the car. He later added a subwoofer.

I’ve always thought the stereo lacked clarity in the bass, and the head unit and EQ have had some quirks. Recently Jeremy pulled the head unit and found all sorts of interesting techniques used by the aftermarket installer that will be the subject of a later monologue … but one of the things we discovered is that the amplifier for the door woofers wasn’t working at all. Swapping it with the amp for the rear deck woofers caused them to go silent and the (shot) door woofers to work again (after resoldering their cut cables).

Turned out to be a delightfully easy fix.

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How You Know the World Has Changed

September 16th, 2010 by Keith Neufeld

On my way to work, I drove past a maybe 12-year-old girl riding her bicycle to school on the sidewalk, kind of wobbling along unsteadily like she’s not very good on a bike yet, helmet strapped on her head and pink backpack on her back, TALKING ON HER CELL PHONE.