RoboStocking - AVR, Servo, Motor, IR Sensor, and BOOM!!! Merry Christmas!

At the office, we decided we were going to have a stocking decorating contest for Christmas. The rules were pretty lax, so I immediately thought of interactivity and electronics and blinky lights and whatnot. Well, that, and there was no way in you-know-what that I was going to hot glue glitter and spongy letters to a stocking with electricity being involved. Here is a video of the final product to pique your interest:

How did I do it? Easy. Some AVR programming (through my usual Arduino hackery) and some simple electronics and BOOYAH! Motion activated stocking with a Santa sign and some jingle bells.

First step was to make a framework to hold the mechanics and the electronics. I used plexiglass and Lexan to support the pop-up Santa sign and to act as the general body of the mechanical works inside the stocking. The layers of plastic were riveted together.

To push out the stocking into shape to make room for the guts, I took extra heavy gauge copper wire I had in my electrical drawer and used pieces of that for "ribs."

The sign was pushed up out of the stocking with a regular hobby servo and some armature work. The plastic worked as a track to keep in straight and sliding smoothly. The armature was made from parts used in RC airplanes I got at a hobby store.

The next thing was to make it motion sensitive. That was initially going to be controller by a PIR sensor, but it turned out to be too whacky. I settled on a nice little sensor by Sharp that I picked up at Sparkfun.com. They simply alter a voltage depending upon what's in front of the sensor and how far away it is. Really simple to experiment with and get a good idea of what numbers to expect from the ADC to trigger the action.

I tried a number of methods for jingling bells. The first was funny, but a bit difficult to implement on the sticking itself. It involved a wheel (or plastic gear, in this case) and a rod with the bells hanging off of it. The idea was that the motor would push and pull the bells rapidly and make them jingle. It worked on the bench, but not in the stocking.

The ultimate solution I stuck with was simply a cam on a motor behind the bells. When it ran, it smacked the back of the front face of the stocking where the bells were hanging. It was essentially a big honking 12V phone vibration motor.

 

Wood cam that vibrates jingle bells

Next step: Jingle bells. I tied them to the cheap Chinese-made stocking with thin copper wire as a sort of twisty-tie thing. Worked great. I wasn't very organized about where I put bells, just wanted to get a bunch in the general vicinity of the bell thwacker motor.

The brains behind all of this is, as usual, an AVR microcontroller. I use my own version of the Arduino IDE to upload firmware to my AVRs on the breadboard. The code is super simple. It basically just waits in a loop for the ADC to show a value from the IR sensor that meets whatever threshold I figgered out in my experiments with the sensor and ideal distances for triggering the sticking. When it gets a hit, it turns on the MOSFETs for the servo (the sign) and the motor (the bells). It start the motor spinning for hitting the bells and pushes up the sign. After a few alternating blinks of the [not-added-at-this-time] LEDs, it retracts the sign and stops the motor and cuts power to them both. That's pretty much it. Here's the RoboStocking motherboard:

I even put holly on the board in the etch. :) Because the wall wart that powers this thing outputs about 20VDC, I put a LM7805 5-volt regulator on the board for the logic stuff and another LM7805 regulator for the motor and servo. There was no reason to run the motor at its full 12 volts. It was only smacking the back of the stocking. There are two regulators because the power draw of the circuitry plus the motor plus the servo was causing the AVR to shutdown. Running on their own circuits gives them each the full power available through the individual regulators.

As always, I drew the circuit board in Adobe Illustrator, flipped it and printed it on my Samsung black and white laser. I've found that running the transfer paper through the laminator four times makes the toner really adhere to the copper without problems. I've notice that after four times, when you drop the board with the transfer paper stuck to it into the water bath, it dissolves off the board pretty quickly. The etch afterward is much higher precision, as well.

The only thing left was to draw a cute sign for the slide-up. It took me a bit of trial and error, but I finally drew a decent cartoon Santa in my normal style and slapped a Christmassy looking font in the sign part of the slide-up thing. This setup makes it look like Santa is just hanging out in the top of the stocking. When he slides up, the actual sign is revealed below him, as if he's pulling it up for you.

Santa sign on RoboStocking

With everything assembled, the guts of RoboStocking look pretty cool:

What makes this story funny is that I was not able to finish this silly thing in time for our company Christmas party. I had to put the final touches on it over the weekend and bring it in the Monday following the party. It was met with great reviews, but could not win the contest that had past. :( Oh, well. There's always next Christmas. Sound and lights will be added, I assure you. ;)

AVR Serial Communications Using XBee RF Modules

I was contacted by Element 14 (Newark.com) recently about doing some product test drives using some of the products from their line card. I took two to three seconds to think about it. I know, tough one...

I have been chomping at the bit to use ZigBee wireless technology in a project. Digi International makes some REALLY cool and easy-to-use ZigBee RF modules that bring ZigBee technology down to a level that even I can implement without more than a few terse passes at a wireless book and a couple of datasheets. So, the first piece of loot I requested from Element14 was an XBee S2 module. I would love to link you to this module at Newark.com, but it appears to be gone. That is sad. BAck to our story... There was a spending limit on my test-drive loot. I ordered one XBee S2 module on my tab. The other XBee module was sent to me courtesy of Element14.com.

The ultimate project is based on a need at our house: We hang out on the back patio quite a lot and when we invite guests over, even after we ask them to just come on in, they ring the doorbell and we can't hear it out on the back patio. The leave disappointed that we would not be home when we said we would be. I'm kidding. Usually they do walk right in.

The first drawring I made used a brass marine-type bell with a string that was routed from the front door around to the back patio. Guests could simply tug on the string to get our attention. My wife wasn't keen on the network of pulleys and string required to make that happen. The drawring above is the watered down, no-fun-havin' version. Awe, who are we kidding? It's still fun. It's ALL fun! What's not to love about electricity and radio frequency waves making things do stuff??

Plan B for the remote doorbell is much cooler and much more electronic: Rig XBee to the house doorbell system so that it can signal a solenoid type of thing to plink a brass bell on the back patio. Not as Wallace & Gromit as the pulleys and string, but still pretty darn cool.

Oh, let me get this out early: Yes, übernerd, I know that XBee is overkill for a simple remote doorbell. The final version of this thing will use a simple little OOK (on-off key) RF module pair that simply sends on or off (button pushed or not). For now, though, this is a great way to get to know Señor XBee and his amigos.

Before I go any deeper into this project, I want to HIGHLY recommend a book on the subject of AVR/Arduino microcontrollers and ZigBee networks. If you're interested in this stuff, go out and get a copy of Building Wireless Sensor Networks by Robert Faludi, published by O'Reilly. I also highly recommend you do NOT do what I did: Do not buy the book, read it cover-to-cover, and do absolutely nothing hands-on. I wound up having to re-read large portions of the book again to get my bearings with the XBee modules from Digi. Try to have an AVR microcontroller (or Arduino) and a couple of XBee modules on hand when you start reading the book.

Now, the first thing I have to say about these modules is that they are stupidly simple to setup and get running, as you'll see in this post. I was asked to do a write-up by Element14.com and this is an easy one: These are AWESOME. There are plenty of sources on the Web for connecting XBee modules. I won't go into major detail, but I will show you how quickly you can get to AVR microcontrollers talking wirelessly with two Digi International XBee S2 ZigBee RF modules. Keep reading...

The process for getting two XBee modules talking, or, in this case, two AVR microcontrollers talking via XBee modules, it this:

1. Get two XBee modules (Farnell.com part 1690810) and a handful of 10-pin, 2mm headers used to adapt the non-breadboard-friendly XBee pins to your breadboard
2. Get one or two AVR microcontollers with UART capability (and supporting components) or one or two Arduinos
3. Build cheesy adapters for the XBee modules so that they fit your breadboards
4. Download the X-CTU Windows program to upload newer firmware and appropriate firmware to the XBee modules (this relates to setting up one XBee module as the "coordinator" and one as the "router" [see book above])
5. Put some serial-savvy code on an AVR chip or Arduino and connect its UART pins to one XBee module's DIN and DOUT pins
6. Connect the other XBee module's DIN and DOUT pins to a serial cable to your computer
7. Send commands through the air to the AVR from your favorite terminal program

OK, that's oversimplified, but if you're comfortable with building circuits and working with Arduino or AVRs, that's all there is to it. Take a look at this setup in action (and please forgive the hastily shot and edited video):

If you're a Mac person, and I know I am, you're going to disappointed in the lack of a Mac firmware updater for XBee modules. However, it is pretty darn simple to fire up Boot Camp or VMware and update the radios the way the aforementioned book suggests. I just picked up my breadboard with the two radios and the AVR and the USB-RS232 cable and plopped it on my desk next to my iMac and fired up VMware and did it. Nice and easy, save for one issue: Once the upload of the firmware was complete, Windows XP Pro went to a BSoD (Blue Screen of Death). Pretty awesome. Let me say that it is no secret that I hate Windows. I'm disappointed in Digi for note having a Mac client to update firmware on the XBee modules. Maybe someday...

If you follow the book, you can get two AVRs or a computer and an AVR communicating in pretty short order. The code I wrote for the AVR to receive the serial commands from the computer to switch the traffic LEDs was easy and it actually worked the first time. It's really cool when stuff works as advertised.

If you've got some communicating you need to do between your microcontrollers, especially multipoint stuff, XBee modules are the way to go. Soooooo easy to setup and use. Head over to Newark.com or your favorite source for Digi International products and start mesh networking your DIY gadgets.

This post was originally about the remote doorbell idea. I'll write a separate post about that completed project using simpler RF modules from SparkFun, as ZigBee is WAY overkill for a remote doorbell, unless you're putting little remote bells or buzzers all over your mansion.

LED Mood Lamp

EDITOR'S NOTE: I've attached PDF files of the pentagon PCB and the motherboard PCB. If I had time to label them and make them pretty, I would, but this was never designed for mass production or consumption. Use at your own risk and frustration. For those with a short attention span, I give you a photo of the completed project (my biggest to date):

If you're interested in the story of this things, continue reading...

This idea came about randomly as a gift idea for my wife. I've built useless machines, clocks, etc. for other people (and myself), but hadn't built anything for my wife. I'm not sure what she's going to do with this thing, but it's the thought that counts.

Initially, this was just going to be a small little desktop thing with a few RGB LEDs on a circuit board with some kinda diffuser. Nothing fancy. Then, while walking through Home Depot, I found a frosted glass globe replacement thing for a wall sconce or lamp or something. It looked cool, wasn't too large, and screamed to have a bunch of LEDs stuffed inside it. I was at Home Depot for something else, of course, but I bought the globe, anyway.

Next, I had to figure out how to illuminate the inside of this thing and make it do more than just cycle through colors. The first thing I did was devise a plane for the "bulb." I decided to go with a dodecagon, which I believe means a 12-sided object. Actually, I had no idea what one of these things was called. I just figured that I needed pentagons to make something more globe-like than a cube. I wanted light to emanate outward from this bulb thing like a light bulb, but with as few sides as possible. The sides were no doubt going to be PCBs, so the less complex, the better. Not that this wasn't one of the most complex circuit boards I've ever built in my short time as a hobbyist circuit builder. Here is the paper prototype:

I'm a visual guy, so I wanted to see this thing in real life and also make sure that it would fit into the opening of the frosted glass globe thing I bought. It did fit. I could handle pentagon-shaped circuit boards. The plan seemed doable.

The next step was to plan out and print the pentagon LED panels for the bulb. As always, I use Adobe Illustrator to design the traces on my PCBs. I don't know if I've mentioned this in other posts, but I tend to lay the components for a project on the flatbed scanner and scan them in, then place them in Illustrator so that I have exact placements for through-holes and spacing on my homemade PCBs. So far, that idea has worked out swimmingly. The planning of a PCB in Illustrator looks like these next photos:

After I get the positions of the LED packages on the PCB, I need to connect them together and to ground, which on these panels were the edges, since they'd all be tied together at their corners. In hind sight, I would have gone the route of a common anode, not a common cathode. It would have been easier to control the individual colors with a simple N-channel MOSFET, as we'll see in a little bit.

Like I did on the LED Reading Lamp project (so far, anway), I just worked out the best routes for the traces that would allow the three different colors to be connected in series. Since the red LEDs dropped less voltage than the greens and blues, all six red LEDs were able to be connected in series with a single 1 ohm resistor. The green and blue LEDs dropped enough voltage that I needed to break them up into sections of three LEDs, which meant a total of five series circuits on each panel. My sketch to figure this out looked like this:

When the circuits were all tied together and the microcontroller and all other parts were together, the ammeter showed a maximum draw of only 270 mA. If it were for the 12 volts that drive the panels, I probably could have run this off a USB port. Oh, well. Back to our story... Here is the final trace design, including the location of the limiting resistors on the back side of the PCBs:

The blue resistor outlines show me where I need to place resistors on the back side of the panels. There are also two jumper wires for spanning out the second green and blue series circuits. I did that because I'm lazy and want to simply solder a 5-pin header through the back of the board. I can't fully explain why, at this juncture. It might have been late and I was tired. Who knows?

Finally, I duplicated the pentagon PCB design five more times and laid them all out so that I could print them together and use a band saw to cut them apart. The gap between the edges is enough for a band saw blade with a hair to spare for sanding and clean-up.

Here is the PDF of an LED petagon PCB: LED Pentagon Panel PCB in PDF form

As always, I used the toner transfer method to print and etch the boards.

If you count the holes and the pads, I had a lot of soldering to do. A completed panel took me about 15 minutes, if my work area was prepped and the soldering iron was ready.

I don't know how ingenious this was, but after the Iron Man arc reactor thing, I needed a more efficient method of soldering SMD parts. My hands aren't steady enough to not flip the little parts off the board when the tip of the iron approaches. I stumbled onto poster gum at the grocery store and a light bulb went on. A super-tiny little ball of sticky poster hanging gum holds the part in-place perfectly and is non-conducting, so it becomes a permanent part of the board, but who cares? The solder looks 2.4 million times better than if I put a weight on the part or I just carefully attempt to get one leg soldered as an anchor.

Here is what the back side of a panel looks like:

On the back, there is a 5-pin header, a single 1-ohm resistor for the red LEDs, and four 120-ohm resistors for each of the sets of green and blue LED circuits. The original thought behind the header pins was that I'd have lots and lots of time to make really nifty plug-in wires for the various panels and they's all converge on the motherboard of this thing for easy modular construction. That was dumb and painful. So I went the cheap and fast route and soldered wires all over the underside of the complete bulb and had just three wires come out for each color, plus a ground wire. Way easier, although soldering all those little wires was a royal pain.

One of these panels by itself was stupidly bright, so imagine what six were going to do:

With all of the pentagon LED panels built, I had to "stitch" them together by their edges to bring all of their ground lines together. Here is a sort of sequence of the bulb being built:

I used bare copper wire to stitch the corners of the panels together. The extra wire was snipped off, of course.

With all the panels stitched together, I had to connect together the color pins from each of them so that I'd have only one wire for each color coming out of the bottom. But, before I did that, I had to see this thing lit up on the breadboard. So, I created, "Squiddy" the LED bulb:

Lit up, Squiddy looked like this (which was toned down so that the iPhone 4's camera wouldn't freak out):

The bulb is powered with 12 volts, but controlled by pulse-width modulation via the Atmel ATmega168 microcontroller. A potentiometer controls the dimming of the LEDs. The other knob on the breadboard is a rotary encoder. This allows the user to change the mode of the lamp from a plain white for reading to an auto-cycling rainbow of colors to a user-selectable color. The built-in pushbutton changes the mode. The rotary encoder's knob changes the speed of the auto-cycling colors or the user-selected color.

Here is a shot I took with my Canon 20D so that a photo could actually pick up the red, green and blue LEDs in the LED packages on the panels (which turned out to be a really cool artsy photo, to boot):

After all that, it seemed like this wasn't that large of an undertaking. Then I realized I hadn't even designed the motherboard OR the case. So, back to Illustrator to design the ROUND motherboard.

As always and as mentioned above, I scan the parts in and put them in the Illustrator document to be sure I get perfect alignment for everything. Yes, the datasheets have great specs for size and positions of pins and such, but I like seeing the parts next to each other on the screen in front of me. I usually put backside items in faint blue so I know where to put the through-holes to the front. This contraption is designed to run off a wall wart power supply, so it can MAYBE go a low as 12 volts (although my testing shows it prefers more) and as high as about 18 or so. 15 volts seems to be the magic number for many of the orphaned wall warts I have in my box-o-wall-warts. The diameter of the the board is about 5 mm shy of the opening of the frosted glass globe. The four screw holes were meant for stand-offs, but I wound up hot gluing a couple of little boards to the bottom of the PCB like table legs because I was antsy to finish it. Nobody see, nobody knows [click click].

Here is the PDF version of the motherboard PCB: Mood Lamp motherboard PCB in PDF form

Toner transfer method means laser printing a reverse image of the traces onto shiny blue model decal-like paper and then heating that face down onto super-clean copper PCBs and then soaking in water until the paper lifts off to leave the toner on the copper:

It look AWESOME at this point, because I've started to run the paper and the copper board through the laminator FOUR times. I'm still getting a little pitting in the final etch, but the traces are generally plenty good for my projects. I'm considering trying the photoresist method to see if I can get higher quality edges on my traces.

Etched and drilled, this baby's ready for parts.

An LM7812 12-volt voltage regulator, an LM7805 5-volt voltage regulator, a couple of capacitors, an ATmega168, and an inductor, so far. With the rest of the parts and a few wires to suspend the bulb above the main board, the final main assembly looks like this:

Again, I felt good having completed this much work on the lamp. That good feeling didn't last long when I realized I had no concept for a case or buttons or anything else. Think, think, think... Ding! Into the garage!

Some poplar, a little router action, a pinch of band saw, and BAM! Rough case:

The top piece of wood has a hole with a routed edge that will "grip" the flange on the glass globe. At the back of the lower piece of wood, I've notched out a place for the power plug and the power switch. The knobs were cut off a poplar dowel I had, for what I have no idea. Put together, the rough body of the case looked like this:

The stained/finished gripper groove looks like this:

A test run of the fitting of all the parts and the case:

The knobs were just sitting on the front of the case. The main circuit assembly was kinda hovering in the opening. I had already hot glued the switch and power port into their respective slots. For added stability and wear protection, the power port was super glued, as well.

As for the final shape of the case, I used the band saw to round the corners. The rest was belt sander city. I sanded the ever living crap out of that thing to get all the sides and edges as smooth as possible. I use this 3X 320 grit stuff that really puts a fine finish on the wood prior to staining. The stain is the same stuff I used on the UME Mark II machines (Useless Machine Ever). It's a combination of stain and varnish that makes it really easy to put a nice color and shine on a finished wood product.

The interior of the case was routed out to allow the wires to go from the switches and knobs to the circuits:

The rotary encoder and the potentiometer were hot glued to beat the band. I'm medium-confident that they will not leave their posts.

I cut out a little ring of felt to cushion the glass globe in its hole in the case. I don't know if it was necessary or if it will provide any protection, since we're dealing with a wooden case. Not like it's glass on steel or something. Eh, whatever. Looks swanky.

Next step: Wire up the controls to the main circuitry. I used strips from an IDE cable to keep it neat inside.

As I mentioned before, the main circuit board is standing on wood stilts held in place by hot glue. It's ugly, yes, but it's inside and it's plenty sturdy:

Here is a video of it functioning, albeit a little flaky, but good enough for government work: