Thursday, April 30, 2009

April maker challenge 21- RFID mouse

I got started late on the AMC, so I'm a few behind. I have, however, managed to average one a day since the 10th. I'm offline at home until May 6 (moved- why do I NEVER remember to arrange things like that ahead of time?), so I'll post my last one now. I have a ton of others, so I'll trickle them out, because I enjoy this, but this'll be it for the daily do.

I'd like to include an RFID reader in a mouse. I think it's doable- some computer mice are pretty large, and by hacking ruthlessly at a hub and RFID reader, you should be able to do it easily enough.

Why, you might ask? Quite simply, it would be a good way to keep your PC secure. Workplace hijinks can occasionally cause heartburn, so I know several coworkers who lock their PC when away from their desks. I'd prefer to have it lock itself after 2 minutes of no action, then have it automagically unlock when I get back to my desk. Thus, an RFID reader that detects a tag I have in a ring I wear and unlocks the computer for me.

Next project- an RFID tag in a ring. :-)

Tuesday, April 28, 2009

April maker challenge 20- POV display

The MiniPOV is an Adafruit toy that provides a discreet package for POV (persistence of vision) display. Normally, POV displays involve lights that are mounted to a moving arm or wheel. As the lights are swept across a person's field of vision, the slow response time of our vision receptors causes us to detect the changing light patterns as an image.

The MiniPOV depends on a person to provide the motion. Instead of being mounted to a moving object, the user holds it in his or her hand and sweeps it through an arc, providing the motion.

That's pretty cool, but it's also kinda small- it fits into an Altoid tin. I'd like to make a larger one- say, 12" long, with one LED every half- or quarter-inch. My deeply subversive application is to press this up against the window of my bus as it drives past all the suckers stuck in traffic on the highway, flashing a message to hopefully get them to consider some alternative to single-commuter driving.

April maker challenge 19- Inductive lamps

I used to have one of those super fancy Phillips electric toothbrushes. One of the cool features of it was that it charged by sitting in a cradle that inductively coupled to the toothbrush handle, so the handle could be sealed water tight and yet still accept a charge.

I'm fascinated by this and by the potential associated therewith. I'd love to try using this for other applications. The easiest is a setup where a coil placed under a table passes power to a device sitting on the table, and the most obvious candidate would be a reading lamp or a centerpiece that has lights involved. The result is a cool centerpiece that lights up without the inconvenience of running a cord across the table.

April maker challenge 18- LED based "candles"

This is a pretty common consumer product: a device approximately the size of a votive or maybe a tealight that behaves basically like a candle, in that it has a small LED that flickers and fades. The reason I want to make one rather than just buying it is that I have a special need- to be able to turn it on and off without contacting it. A few years ago I made some balsa and paper lanterns that can be hung from the ceiling on a string. A tealight in the bottom provides nice light, and the dozen or so that I made create a very warm atmosphere in a room where they are the sole illumination.

Of course, lighting all those candles is no fun. It requires hauling a chair around the room, getting up and down, and trying not to catch the paper on fire. Putting them out is similarly taxing, unless you let them burn down over four to five hours. Obviously an application ripe for electronify-ing, but an electronic light has the same problem: to turn it on, you need to get up on a chair, pull the light out of the lantern, turn it on, and drop it back in. I know, not SUCH a huge deal, but still more than one wants to do regularly.

So, my solution is a pretty simple one: make the lights magnetically switched. It's pretty simple to do- just put a reed relay in the system and drive the thing with a PIC. The PIC stays in sleep mode until you activate the relay, then it flickers the LED until you activate the reed relay again. Activation of the reed relay just requires waving a magnet on a stick near the lantern. A PIC in sleep mode can sit in a circuit with a couple of AA batteries for months without draining them.

April maker challenge 17- Tachometer glove

Four, this time, because I know I'm going to go today and tomorrow without having another chance, since I'm moving tomorrow and I'm not going to have Internet access at home or work (eep).

Tachometer glove for race driving- I USED to have a zippy car (VW Jetta GLI), and I always had a hard time knowing where the tach was. I thought it might be nice to have feedback that didn't rely on vision (because taking your eyes off the road at certain times can be...dumb is the best word I can find) or sound (because open windows, music, road noise, and other things can distract you from the actual sound of your engine.

My idea was a pretty simple one- you put a pager motor on the back of a glove that fits snugly, so that the motor is held tightly against the bones to get maximum sensation. I'd guess a wireless link (Zigbee or Bluetooth or IR or whatever) would be most appropriate, and the motor would vibrate at a frequency either equal to or proportional to your engine RPM, providing simple physical feedback that is hard to obscure.

Saturday, April 25, 2009

April maker challenge 16- portable collapsible squat bar for birth

My wife is pregnant. She is very interested in pursuing natural childbirth practices, and one of those is the idea that squatting during childbirth is preferable to being flat on the back.

We have some concern that our chosen birthing "venue" (Fairview Riverside) may not have the necessary item for facilitating this position, and I desperately want to support my wife's birth plan, so I'm thinking about figuring out what exactly is required for this and trying to make it real and portable in the next six months. I'm guessing there are other women out there who might want this sort of thing as well.

Friday, April 24, 2009

April maker challenge 14 and 15- camping stove and micro-preamp

I'm just going to give up trying to do one a day and go for two every two days. It seems more believable for me.

I have a small interest in camping, which I'd like to make into a larger interest in camping. One of my very favorite camp toys is the penny stove-an ultralight alcohol fueled stove made from two Heineken cans and a penny. Yes, they do have to be Heineken cans- the shape is important.

I have two of these little fellas and they work GREAT. A few mL of denatured alcohol into the stove is enough to boil a quart of water long enough to cook noodles, or make rice, or whatever. There are three other things I'd like to make in relation to these, though- a heat concentrator, a nice stand, and a larger burner version. In reverse order:

Heineken comes in 12 ounce cans or 24(?) ounce cans. I'd like to buy a couple of the big ones and make an uberstove. Just for kicks.

My current stands are two bent-up coat hangers. They require fairly level ground and are kind of wobbly. I'd like to make something more sturdy, possibly collapsible and possibly with a bit of leeway for unstable or unlevel surfaces.

The last I'm stealing from another AMC post: a heat concentrator. I'd like a highly portable and very easily used device that wraps around my stove, stand, and pot, which keeps the hot air coming up off the stove flowing along the sides of the pot instead of letting it disperse. I'm expecting this would make the penny stove much more efficient.

Next idea- micro-preamp. I have an interest in foley artistry (not that I've ever done anything about that interest) and I always have my MP3 player with me. My MP3 player has an input jack which apparently has a fairly high high input impedance. I also have a tiny little microphone which has a fairly high output impedance. I'd like to make a super-simple lo-fi amplifier that I could plug in to the MP3 player for when I find a really fun sound in the environment. I could then later collect these sounds, play with them, and possibly offer them to the world. Ideally, it would be powered by a button-cell battery and have an off switch to avoid draining it too badly (although that might be unnecessary if I design the circuit right). In fact, a REALLY fun trick would be an amplifier that could work on a charged capacitor rather than a button cell- must consider that.

Wednesday, April 22, 2009

April maker challenge 12 and 13- Jacob's Ladder and raised garden beds

Two-fer today, to make up for yesterday. I wish I could get it together and post daily.

The first is a simple Jacob's ladder. I've always wanted one of these and it's an affront to my tinkering nature that more than 10 years after I started into electronics, I still haven't made one up.

The second is a raised garden bed for my vegetable garden. We'll be moving next week (eep!) and I have no interest in tilling up a large patch of yard in a rental property, and I'll need to buy some kind of soil to make it support plants anyway (there's little chance of success in the area I'll be living in without doing so, due to the advanced age of the neighborhood), so I'm thinking I'll build beds on legs, about two feet high and four feet by eight feet. I figure that'll make it easy to work them, and you should be able to reach the middle pretty easily. Good drainage, etc.

My company has a demo dumpster FULL of old shipping crates made of 1/2" plywood with a 2x4 frame. These should make wonderful box bottoms. There's other wood in there, too, that'll be perfect for the legs and sides. Free is good!

Monday, April 20, 2009

April maker challenge 11- IRduino

I like the Arduino as a simple computing platform, but I've mentioned here before that I'd like to offload some of the more basic functions to a co-processor to let the Arduino have more CPU cycles for other stuff.

That's true for many, MANY tasks, and one of the ones I've been fascinated with since college is the capturing and parsing of data from an infrared remote control. Adding IR to your project is a SUPERB way to add very complex I/O.

I'm not sure if the Arduino has a library to read IR from remote controls, nor do I care, because it's likely to suck up an unacceptable number of CPU cycles. Thus, the IRduino: a shield with a small microprocessor (I'll probably use a PIC, since I know how to work those much better than AVRs) which decodes the signals from infrared remotes, packs it into three or four bytes (there are actually a LOT of possible codes out there, due to the number of encoding schemes). There would then be several options for sending this to the Arduino- a semaphore based scheme, a "dump-on-receipt" option, a "hold-until-request" option. Others, perhaps.

April maker challenge 10- Self-destructing USB drive

So, since DHS can swipe your stuff at a security checkpoint for no good reason, I've been thinking I might like to make a self-destructing USB drive.

There are two possible tacks for this: one, a "snappable" drive where there's a small ampule that one would crush (a la cold war suicide pills) that connects an on-board 3V lithium battery backwards across a couple of pins, roasting some silicon and making the drive pretty much irrecoverable. I guess in the end, it would be difficult to completely wipe out the entire flash matrix, but it's a start. This has a disadvantage in that you need to KNOW someone is ABOUT to take your flash drive away in order to activate it.

The other method is a simple wire and switch method, where the drive is modified to reverse the 5V and ground unless the user does something to reverse that. The easy way is to put a switch on the drive which has to be flipped; that of course draws attention to the mechanism. A subtler method involves an internal reed relay that requires a magnet to be close to it in order to operate safely. That's less discoverable, but you're more apt to accidentally forget to do it and kill the drive yourself.

Of course, if one were to productize this, it would fail instantly, because DHS would become aware of it and all would be lost. You also need to make the hack relatively invisible; if it's not, you'll draw additional attention and make it MORE likely that the drive is confiscated.

This is, of course, the Sunday project. Another will follow later today.

Saturday, April 18, 2009

April Maker challenge 9- mixer to food mill adapter

In canning, when making sauce or jelly, the easiest way to go is to use a strainer to separate seeds and peels from the desired fruit meat. The drawback is you get crank arm eventually, because you have to turn the crank for sometimes up to a couple of hours at a stretch and, while it's not terribly physically demanding, the long throw of the crank means that your whole arm is involved which can really wear on the joints.

To that end, I've decided to make myself an adapter that will let me join my strainer to the PTO (or whatever it's actually called) on the front of my KitchenAid mixer. I bought a couple of universal joints at Ax-man that should do the trick nicely (necessary because the height of the mixer PTO and the height of the mill axis are not the same; I considered making a platform that the mixer can sit on and the mill could clamp to which would position the two machines to be coaxial but frankly, I'm not crazy about having to line them up THAT carefully every time, so two U-joints it is). This is going to take me a couple of hours in the machine shop probably, but since I had the mill already, buying the attachment for the mixer would have felt like a waste. Plus, I like the idea of being able to drive it by hand if necessary.

Friday, April 17, 2009

April maker challenge 8- Outdoor canning kitchen

Canning in the house sucks. It involves putting a pot of water on to boil for hours at a time (some canned goods must be boiled for 30 minutes or more, and if you're doing it, you probably want to do enough to make it worth your time, so that means several rounds), tying up the whole kitchen, and release about a bazillion joules of heat-energy into your home. By the way, did I mention that this can only be done during the hottest months of the year? Yeah.

Beth and I are moving into a rental house in a couple of weeks, and I'd like to make an outdoor canning kitchen (I bet you though ALL my projects were electronics...). What I have in mind is a couple of those turkey deep fryer things, connected together through some kind of Y-valve, with a nice frame of some sort to add stability. A bench, too, probably. I can't build this stuff in because this is a rental, so it'll be an interesting challenge to see how I can do it.

Thursday, April 16, 2009

Superhack power supply

(click to enlarge)

I'm not going to count this in the April Maker challenge. I don't know why.

I hacked together a really hokey power supply for my tabletop foam cutter and as-yet-unbuilt acrylic bender (although strictly speaking, the portion of the foam cutter heating element that runs underneath the acrylic "table" has done a nice job of melting it). JTBarclay is using it for driving a 24V nigh-5W fan under a stir-plate, and Pat is building one for HIS foam cutter.

It does a fairly good job, although it has no check on the amount of current it draws from the unregulated DC supply, which is a MAJOR short coming. The IC is an 8-pin PIC that I've programmed with a PWM controller that reads a pot to determine the duty cycle (at least, in this configuration it does). Because of the way the design works, you can put a limit on the duty cycle by inserting a resistor between the potentiometer and the ground rail. Using a smaller potentiometer is wise if you were going to do that- you want to keep the overall resistance down. The larger the resistor, the lower the maximum duty cycle will be. If the resistor is equal to the value of the potentiometer, you'll be limited to a 50% duty cycle; if it is twice the pot's value, you'll be limited to 33%. The equation is Rpot / (Rpot + Rbias), where Rbias is the value of the added resistor.

April Maker challenge 6 and 7- Mini-lathe and RepscRap

I keep falling behind, but I'll not be more than one day back, dammit!

Number 6- A mini-lathe. One of the most common things I use a lathe for is the drilling of a concentric hole (or reaming one out) in a circular object (gears and wheels, for instance). I don't need a super-accurate means to reduce a diameter or things like that, just a way to put a hole in the exact center of a gear when I'm trying to mate it to a particular shaft (of a potentiometer, or encoder, or what have you). I guess "lathe" is the wrong term, but it's the best I have.

Number 7- RepscRap. The RepRap, of course, is the open-source self-replicating 3d part printer. The RepscRap is an extension to that, a device which allows the reclamation of plastic material of appropriate composition by shredding it, melting it, and extruding it as a stick or rod the can be re-used in a RepRap. The material would be recaptured from junked electronics, pop bottles, or whatever uniform source of approrpriate material. Of course, I need to make a RepRap before this matters.

Tuesday, April 14, 2009

April maker challenge 4 and 5- Acrylic bender and tabletop foam cutter

I'm a day behind so it's a two-for-one, but a quickie, because I'm behind in every possible metric my life could be measured in.

Number 4 is a tabletop hot-wire foam cutter. Imagine a scrollsaw or bandsaw, but instead of a saw blade, using a piece of hot wire. It excels in cutting intricate shapes out of pieces of expanded polystyrene foam, and can be used on other thin and low-density plastics as well.

Number 5 is an extension of this. By putting the hot wire at the edge of a table, along the corner, a piece of acrylic can be heated evenly along a line, which will allow it to be bent.

Both of these use the same power supply. That will be described as a future project.

Sunday, April 12, 2009

April Maker challenge 3- Tamiya servo conversion

Tamiya is a Japanese company that makes many hobby-type products- model kits, "experiment" sets, RC toys, and others. Deeply buried in their product line is a set of generic motor/gearbox combinations.

These range from very simple to very complex; I have a couple of their high-power ones, and one of the 6-speed ones as well. They are well constructed, fairly tightly toleranced, and loaded with features. The have a twin-axis gearbox, a worm drive gearbox, and a planetary gearbox, in addition to more "standard" types. Typical cost is between $10 and $20, depending on the model.

One of the most enjoyable items in the hobbyist robotics arsenal is the RC servo. However, most servo motors tend to be either pricey or weak, and they tend to be non-reconfigurable, meaning that you can't readily trade off speed for torque or vice-versa.

To that end, I'd like to make a small PCB that would let me take an input from a shaftless potentiometer attached to the output shaft of a Tamiya gearbox and turn the gearbox into a servo. Target cost would be $10 or less in parts, because that puts a Tamiya gearbox + this circuit in a price range to be MUCH better placed than a comparable servo.

Saturday, April 11, 2009

April Maker challenge 2- servo driver IC

Lately I've become obsessed with multiprocessing solutions for hobby level embedded systems. A PIC12F683 is a reasonably powerful 8-bit microcontroller in an 8-pin package, and it sells for right around $1 in qty 25. This can provide a powerful means for offloading certain functions of a circuit to another IC at minimal cost, allowing you to do heavier lifting in your main circuit than you otherwise might have. An example is servo-motor control with the Arduino. It's quite do-able, but you may find yourself in a project where you want to control a servo's rotational position based on user input from a potentiometer. In that case, using precious CPU cycles from the Arduino in the system just to read the pot and update the servo periodically is a drag. So why not take an 8-pin PIC and make a simple IC that reads digital inputs and converts the value to a servo angle?

It'd be easy enough- the servo output is a PWM signal but the duty cycle is low. The motor holds position expecting a pulse every 20ms, and the pulse is usually in the range of 1-2ms for 0° to 180°. That leaves you a minimum of 18ms to read the analog voltage(s) and calculate the next pulse length. At 8MHz (the maximum internal clock speed of the '683), each instruction is 500ns in length. If we do 8-bit math, we can have 256 variations representing 0° to 180°. Making the assumption that the pulse needs to be 1.5ms +/- .5ms, we have a 1ms dynamic range to express with 256 slices- about 4us per slice or 8 instruction cycles. I think that's probably enough time to do a pretty accurate timing routine for three channels, using three analog inputs, which is handy, because the '683 has 6 I/O pins, so that's three analog ins and three pulse outs.

Friday, April 10, 2009

April Maker challenge- project 1

Over on the TCMaker web forum, a challenge was levied to all of us to come up with one project every day during the month of April. I'm behind, because I've been VERY busy preparing for and teaching my intro to electronics class through Studio Bricolage, but I'm going to try VERY hard to keep up with it for the rest of the month. Hence, the new blog.

Project 1: Airsoft pellet gun organ
Ax-man sells Airsoft pellet guns super cheap (~$10 for a pistol). I'm thinking it might be fun to try to make a pipe organ that articulates based on having the pellets fired down the pipes, which would then dump the pellets into a bin for immediate re-use.

It might get pricey, since I'm thinking I'd want the seven major notes, but I'm not sure how I'd go about tuning them or even what effect firing a pellet down a tube would have. Still, it might be cool to try out.