So, it appears that after all my lofty proclamations about posting more often, somebody, as they say, thought they had a better idea. And it wasn't me, honest. Well, maybe it was me just a little bit. Okay, 100%. Whatever.

Anyway, I have got the most delightfully tedious trivia for you. As I've mentioned, I've been tinkering with an old Mobile Armatron with the aim of putting it under autonomous computer control. I partially rewired the motors and built a small power supply for the eventual onboard logic, and then began on a motor controller that would fit in the Armatron's "trunk space". I ordered a few L293 chips, since they seemed to be ideal for the purpose, and lots of people seemed to like them.

Unfortunately, I learned that setting up the circuit on a piece of protoboard would definitely not work. I ended up with a spaghetti nest of jumper wires that was so thick I couldn't even fit them all in. Obviously, I'd have to design a board. I set that project aside for a while in order to do some reasearch on how to do that. I finally discovered three techniques which made it relatively easy.

One discovery is Eagle, a printed circuit design application, which makes designing boards easy (for limited values of easy.) You draw your schematic out in the schematic designer, choosing parts from a vast library and wiring them together. It is not a launch-it-and-go application. Eagle is quirky and odd and has a definite learning curve. I would definitely advise anybody to run through a few tutorials before trying to design a masterpiece. It took me a few hours, but I did get the hang of the basics.

The next discovery was of the toner-transfer resist method. Laser printer and copier toner can be transfered from paper to a copper-clad printed circuit board with the use of a simple clothes iron. Of course, using the correct sort of paper makes a big difference. It's been said, and I must agree, that magazine paper works quite well.

The final piece of the puzzle was the cupric chloride etching method. A reusable etching fluid can be made by combing ingredients from both the drugstore and from the hardware store. And it works pretty well. I did notice that the etching process was pretty slow, but I eventually realized that was because it was a cold night. I had set my etching container in a Pyrex dish to catch any spills, so pouring hot water into the dish warmed the etchant and sped things along.

So, you may be wondering, what do I have to show for all that work? Well, it looks sort of like this:

Here's something we haven't done for a while, but someone did submit a good question, and it deserves a good answer.

Q. Where do you find the best parts to scavenge for robotics?

A. Just as the best food for fish is fish, the best parts for robots are robot parts. However, finding a dead robot from which to scavenge parts can be difficult under normal circumstances. So I have prepared this list, based on my own experience, of things one is likely to find in normal circumstances, and of what useful things one might find inside those things.

Computers

Power Supply

Not worth scavenging parts from as it contains large capacitors which can be quite dangerous. However, AT/ATX power supplies are quite useful to the experimenter as they deliver a useful range of voltages: +12, +5, -5, -12, and 3.3 volts. If you're using an AT power supply, ensure that the switch is adequately insulated to avoid an electrocution hazard. You will also need to supply a load for the power supply to work properly, such as a large resistor. Perhaps you might consider building an enclosure for the switch, load, and power supply with spring-loaded terminals for each voltage. Although I do not recommend opening the power supply, this page is still helpful. And here are some other ways to get power from a PC.

Motherboard

Very old motherboards are treasure troves of 7400-series chips, kilobytes of memory, and some specialty chips like UARTs and processors. However, unless the board is bad, first consider whether it might serve you better as the brain of your robot.

Expansion cards

As with motherboards, very old expansion cards are even bigger troves of 7400-series chips. People are usually happy enough to get rid of their old modem cards, and these usually have relays, which are useful for controlling motors, especially larger ones.

Floppy disk

I don't get too excited about 3.5" floppy disk drives as the stepper motors are pretty small and haven't proven that useful when removed. On the other hand, 5.25" drives, if you can still find them, have much larger steppers. You may find a stepper motor driver on the board if you're extremely lucky, but in my experience, the steppers are driven by the drive's CPU either directly or via a transistor array. You might also, with some research, be able to get the pancake motor (that spins the disk) to work. On the oldest 5.25" drives, the flashing of an infrared beam shining through a hole punched in the disk was used as a timing signal to keep the motor spinning at 300 RPM. Other pancake motors use magnets instead of a beam of light to accomplish this.

CD-ROM

You can usually find two to three DC motors in a CD-ROM drive: one to spin the disk, one to move the laser, and one to move the tray. You'll also find some gearing assemblies in conjunction with the tray that may or may not be useful in making a linear actuator. If you look on the board, you could find a few audio amplifiers, a DC motor controller, or a microcontroller.

Hard disk

Unless it's very old, there won't be a lot of useful parts except for the neodymium magnets. These have all sorts of uses, particularly in attaching heavy objects (like bulletin boards) to metal objects (like your refrigerator.)

Mouse

You'll find a few microswitches, and either a pair of rotary encoders with infrared emitters and phototransistors, or a tiny camera.

Printers, fax machines, copiers*

Here's where you'll find a few motors and loads of gears, cams, rods, springs, and pulleys. In inkjet and dot-matrix printers, you'll also find a screw or belt that drives the print head back and forth. There will probably also be an encoder disc or even a strip that the printer's CPU uses to ensure that the print head is in the right horizontal position.

Entertainment

Stereo*

Loads of analog components. If it's got a CD player, see CD-ROM. If it's got a tape player, there will be at least one DC motor and perhaps a belt system. You may also find a DC motor controller.

VCR*

You'll probably find at least one DC motor and motor driver. You'll also find a few gears and belts, and an infrared detector.

Televisions (and monitors)*

Not much besides a few analog components such as resistors and capacitors. In fact, old televisions often have especially large capacitors inside, which can be dangerous if not properly discharged. I would avoid these entirely.

* Take care when opening such devices. Unlike your friendly neighborhood PC, the power supply in one of these devices is unlikely to be shielded, and even if the device has been turned off and unplugged, large capacitors can store a hazardous amount of voltage for a surprising amount of time.

Q. I've asked my friends to give me their broken appliances so that I could scavenge parts from them. Now I have so many circuit boards lying around that it takes me longer to look for a chip than it does to remove it from the board. How can I get more organized?

A. I had this same problem. The answer is to create a database. With the work of an hour or two, you'll soon have all your parts at your fingertips. And if you're a Windows user, chances are you may already have all the tools you need on your computer. I'm talking about MS Access. Sure, professional DBAs may scoff at this program, but it will be sufficient for cataloging a few hundred components. On the other hand, if you're an ambitious Linux user, you might be well-served to look into a Linux-Apache-MySQL-PHP (LAMP) solution. Whichever route you take, plenty of books and Web tutorials are available.

When I set up my database, I created tables for each sort of component I wished to track. For example, the IC table looks something like this:

The Container field points to a record in the Container table, which represents either a circuit board or other container (such as a drawer of loose components):

The Location field points to a record in the Location table, which represents the various boxes and drawers used for storing Containers:

Now if I ever need an L272M, or an Op-Amp in general, I can query the database, which will tell me that there's one on Brownish board marked LP1-CD MBD in Cardboard Box #1 .

Welcome to the second installment of q+=a, The Electronic Replicant's new question-and-answer feature. As nobody has actually submitted a question yet, I'm going to consult my referral logs again.

Q. How can I control a 120VAC motor with a BASIC stamp?

A . This should not be too difficult if all you need to do is turn the motor on and off. Now, it is important to remember that I am not an electronic engineer, nor do I play one on television. I am also not an electrician, with which one really ought to consider consulting before trying to build anything that interfaces directly with wall current. The following ought to work, but it could just as easily electrocute you, catch fire, or otherwise malfunction. You're probably better off buying an X-10 module.

Still there? You are obviously an individual of unswayable fortitude, or perhaps you have simply fallen asleep at the keyboard. In either case, what you'll need is something along these lines:

This is quite similar to the motor controllers I mentioned last time. A pulse from the BASIC Stamp (or other microcontroller, or your PC, or whatever else) causes the LED side of the optocoupler to emit light and thus trigger the phototransistor side of the optocoupler. The transistor energizes the relay coil, creating a magnetic field which closes the contacts, allowing AC to flow from the plug to the socket, thus powering your motor, Christmas lights, fan, pump, or whatever.

A nice thing about this circuit is that the optocoupler will protect the Stamp or PC from destruction by high voltage if the relay happens to short, which is not likely, but it could happen if the current flowing through the contacts is much higher than what the relay is rated for. That could also lead to the relay melting and/or bursting into flame, which is just not a good thing. Of course, the optocoupler is really effective only if the PC and relay are on separate power supplies.

That concludes this installment of q+=a. If you've got a question you'd like answered, or if you think my answers are utterly and completely useless, or both, or neither, please leave a comment at the prompt.

Rather than posting another Robot Update that says nothing of importance except that it's been a while since the last Robot Update, we're going to try a something new, a question-and-answer column! Now, since nobody's actually asked me anything directly yet, I'll instead respond to a hot(ish) search topic.

Q. Control cordless drill motor with basic stamp

A. Although your query was phrased less than elegantly, I'll attempt to answer what I assume is a question. A pair of cordless drills or electric screwdrivers may be the ideal propulsion system for a combat robot. Consider the advantages: built-in gearbox, adjustable speed and torque, and modular, self-contained rechargeable battery packs. They can also be obtained for a relatively low cost, especially when compared to buying and/or fabricating the components separately. They can also be considered to be easily replaceable, another advantage to a combat robot.

Before we begin the interesting part of this article, I'd like to point out that I am not a professional electronic engineer, nor do I play one on television. This is also not a step-by-step tutorial on hacking your rechargeable drill. This is just me telling you very generally how I would go about doing it. It could work, but then again, it could explode in your face, set your house on fire, frighten your children, or just plain not work. I haven't actually tried it, so I don't know.

Still there? Good. Let's take a look at the guts of a cordless drill.

You'll notice that the on/off switch and the speed-controlling rheostat have been removed. That's fine, as I wouldn't be using them. You'll also notice that the battery jack and the case are missing. This is so that I can make a point. Below, you'll see the equivalent assembly from a remote-controlled dune buggy.

Notice anything? That's right, they're not all that different. So at least one way of controlling these motors should have just occurred to you. If you're building a remote-controlled combat robot, off-the-shelf RC controllers will probably fit the bill.

But since you also asked about BASIC Stamps, I assume you're going to want to program your robot, rather than just puppeteer it by remote control. That's fine, too. In that case, I'd build my favorite motor controller, the old-fashioned electromechanical H-bridge. I'd choose this over a transistorized or solid-state controller mainly because I don't know what voltage the drills will be using. Relays can typically handle 120V AC, so handling 12V-36V DC shouldn't be a problem. Also, the brushes of the motors can introduce a lot of noise into the power supply, and this method will physically isolate this noise from the control circuitry. And finally, listening for the clicking of the relays can be a valuable troubleshooting tool.

Here's the schematic.

Typical parts are 1K resistors, 2N2222 transistors, and 1N4003 diodes. I try to use 5V relays in order to avoid the need for a 6V or 12V power supply. However, if the design of your bot means that you already have a 6V or 12V bus, then by all means use it.

The finished product might look something like this.

There are, of course, some drawbacks to this circuit. The main drawback is that the motors will always run at a constant speed, as determined by the supply voltage. This may be what you want. However, a robot that can only go full speed ahead could be difficult to maneuver. I would suggest the following modification if you want speed control.

This version will use a big fat power transistor in place of the SPST relay. You could then feed a PWM signal from the BASIC Stamp to the transistor to control the motor's speed. I'm told the diode across the pins of the transistor is necessary to protect it from backlash voltage when the motor shuts off. Hopefully I've got it in the right place. Values of these parts depend on your motor.

The finished product might look something like this:

This concludes our first installment of q+=a. If you have a question you'd like answered, go ahead and leave it as a comment. Also, if you don't like my answer, go ahead and leave that as a comment. See you next time!

It appears my humble abode on the Web is finally getting visitors. Good, good! (cackle cackle).

Upon analysis, it would appear that most of the visitors are new and are arriving from the NaBloPoMo list at fussy.org and also the randomizer at pinkelephants.org. But, a few visitors have arrived via search engine, seeking a "Ballbot VCR" and "UCN5804B Scrounging"

Well, I can't tell you how to build a Ballbot from an old VCR, but I can tell you what I know about the UCN5804B. This discontinued chip is apparently rather elusive. Unfortunately, I have no idea what devices these stepper motor controllers were ever used in. I got the few I had from Newark Electronics quite some time ago. Now, if one wants only to drive a few stepper motors, might I point out that most of the floppy drives I've dissected so far use Darlington array chips to drive their stepper motors. One might be able to use one of those, a latch and a shift register to mock the functionality of a stepper driver. It's just a thought. But if you're trying to repair a particular device, ough. Best of luck to you.

In other news, on Monday, I got yet another electronics book from paperbackswap.com . If you haven't heard of this site, (and you'd like to swap your boring old books for some interesting new ones) do check them out. It's rather like netflix for books, and your only cost is postage.

The only problem with this particular book is that its last owner was apparently a smoker, so it was a bit smelly. I thought maybe slipping some dryer sheets between a few of the pages might help. It did. Now the book smells like a motel, rather than an ashray, which is a slight improvement..

Following a link from RootPrompt about a proposed Heath Robinson Rube Goldberg Computer , I learned of this relay-based computer constructed by Harry Porter of Portland State University. The picture gallery tells most of the story, but on the second page are a video, sounds of the computer in operation, and even a PowerPoint presentation explaining how it operates.

Make: brings us an article on another homemade computer , this one built almost entirely from transistors. Three thousand surface-mount BC847/BC857 low frequency transistors make up the registers, arithmetic logic, and other units that are typically integrated into the microprocessor in today's computers. The MT15 runs at 500 kilohertz and has 128k of RAM, which is not transistorized.

This shows that "because I can," is often reason enough.

Meanwhile, Slashdot reports on the Open Prosthetics Project , a collaborative endeavor in which the share-and-share-alike Open Source philosophy is applied to prosthetics. I'll be watching this project with interest to find out how quickly it can get from peg-leg to cyberpunk .

Remember the LCD panel I salvaged a few weeks ago?

Well, I finally put it to use. As it happens, I am setting up a small multipurpose server for my home. The motherboard I'll be using happens to have NTSC out, and this LCD happens to have NTSC in. So not only could I use this LCD as a mini-monitor, I could also dress it up and use it as a digital picture frame. So that is what I did:

I would say that the most difficult part of this project was figuring out where to get weird voltages such as +8v and -5v. The +8v source was relatively simple. Since the inverter powering the backlight required a +12v supply, feeding this also to an LM7808 regulator yielded the +8v. Since the PC power supply I use for testing does supply -5v, I actually considered tapping off the power supply in the server until I discovered that the server's power supply omits the -5v line. But I soon discovered this circuit , which uses a 555 timer and a few diodes and capacitors to produce a negative voltage, which not only worked, but also allowed me to power the entire project with a common 12v wall wart.

I also found this handy Capacitor Value Calculator , which translates the arcane three-digit codes on ceramic capacitors into the actual capacitance value.

Hackaday 's hack of the day is this microwave oven arc welder:

Although I do happen to have a discarded microwave, and I do want to learn to weld, this project requires eight transformers, not just one.

Make: presents HOW TO - Make a digital toy infrared camera.

I did this myself, a while back, using a SiPix Blink II, the gel filters described in "$10 Infrared Goggles" , and a few pointers found here. Although the Blink II was never designed to be taken apart, I managed to do so without destroying it. It was then that I learned that the infrared blocking filter was of the sort bonded to the lens. Fortunately the lens appeared to be interchangeable with that of a security camera I had. So I borrowed that lens. I would come to regret that later.

At any rate, I managed to get the Blink II reassembled and set out on a grand day of photo taking. Unfortunately, I had forgotten the Blink II's major drawbacks. Not only does it take worse pictures than my cellphone, it sucks batteries dry within a few hours, and of course all of your photos will then evaporate at that point. So guess what happened?

Yes. I returned home empty handed. I tried (with fresh batteries) again and again, until the time I finally made it to a computer in time to download and view this:

Here's the complete photoset .

Oh, and the reason I came to regret using the borrowed lens? Well, a few more dead batteries and lost photos later, the experimental camera suddnly found itself flying into the bushes at the Lake Murray reservoir.It was never seen again.

Make: has an article on scrounging electronic parts: "This article describes a recent scrounging project on a 3Com SuperStack II switch. This Ethernet switch was purchased to use in a home network for $10 at a Goodwill computer store. Unfortunately it was discovered later that the device had very loud fans and was actually only a 10MBit switch. Instead of just throwing it away, it was gutted for parts."

I must say that salvage is an excellent source of parts for many a project. I discovered a pile of discarded exercise entertainment systems, which yielded dozens of PICs, voltage regulators, cassette players, and most importantly, miniature LCD screens. The units as a whole appeared completely nonfunctional, but on a hunch I extracted one of the LCDs, and...

True, your friends or spouses may ridicule your penchant for bringing home "junk", may bemoan the space your collection is wasting, may plead you for the love of God to throw some of it, any of it, away. To them I say that junk is something that you throw away right before you finally need it.

I just completed a set of whisker-type sensors for my soon-to-be mobile robot. I had seen several such designs elsewhere on the Web, but each had elements I didn't like, such as that the antennas were electrified. I eventually arrived at the hybrid design shown below.

In this design, one end of a spring is soldered to a PCB, but the other end is left free to move. A U-shaped loop of wire surrounding, but not touching, the free end of the spring is soldered to the PCB. Then, an insulated probe is inserted into the free end of the spring. When the probe collides with an obstacle, the spring moves and makes contact with the loop, completing the circuit.

Here's the finished product.

Yesterday, I completed my fifth motor controller board, containing two of Steve Bolt's Four Transistor H-Bridges  The first was an old-fashioned SPST/DPDT relay controller, the second was based on a pair of BA6219B chips I salvaged from an old VCR, the third was a UCN5804B stepper driver, and the fourth was a set of pure transistor (TIP41B) H-bridges. Since I can now control up to 8 DC motors, and since I'm pretty sure I can throw future motor controllers together whenever I need them, I think I'll move my attention to sensors.

I think I'll start with such low-tech sensors as bump switches and CdS cells. I like the idea of giving my robot feelers, but I haven't seen a design for them that I've really liked. As for CdS cells, I think I'll just go with a four-cell design I found in Robot Building for Beginners