Soft Circuit Swatches with Surface Mount LED

Creating small electronics out of uncommon materials is a hobby of mine. I think it’s fun to show that electronics isn’t limited to circuit boards, and computers don’t have to be stuffed inside boxes. Especially when FabLab is exhibiting for school age kids who might change their minds about whether they’re interested in CS and ECE, I’m happy to show off a wide variety of computers, usually various arduino-powered objects.

Aside from having interesting widgets to show off, I mostly enjoy the challenge of building something with materials I haven’t seen used before. Instead of sewing LEDs on top of fabric, I wanted to integrate the LEDs into the fabric, so I used a hand loom to make a patch of fabric, using stainless steel thread as my weft. Knots have never made sense to me, so setting up the loom was especially challenging.

I really can’t think of anything to do with this, so for now it’s just a tech-demo. I’d love to hear your ideas.

I really appreciate what Adafruit and Sparkfun do to make small electronics available in sew-able packages (such as the Flora and Gemma microprocessors from Adafruit, and the Lilypad from Sparkfun), but I never really liked that the components were still bonded to a chunk of fiberglass circuitboard — it limits the flexibility of the fabric where it’s sewn and it looks bulky. With that and the extra expense of those products in mind, I wanted to come up with a strategy that allows surface mount components be embedded into a flexible material. SMD is the cheapest package for many parts — we order these 1206 size LEDs at 2 or 3 cents apiece on eBay.

Stranded copper soldered directly to these LEDs are sewn into leather which was lasered to punch holes and provide guides for the wire. This is just a test swatch, I have it in mind that lasering the holes and traces like this would provide a way to wire fairly complex 2-layer circuits (since traces could cross to opposite sides of the leather to avoid intersecting). The parts can sit flush with the surface of the leather, and the leather can flex without dislodging the parts — they aren’t bonded to the substrate, just pulled against it by the copper stitches. This also makes it surprisingly repairable. At one point I melted an LED after stitching everything together, and it only took a minute to un-solder and drop in a fresh LED.

For the leather circuits, I’m looking forward to trying to do 7-segment displays with the same LEDs, but embedded the microcontroller and battery holder directly into the material. I’m imagining interesting tabletop radios and clocks that exhibit their circuitry on their surface.

A quick demonstration of both circuits:

The doorbell has a boring sound. We can fix it.

ATmega328 + JQ6500 MP3 tutorial

Fellow Xin Che Jian member LuFeng came in with a good project and a stack of microchips: Microduino modules that can be programmed to play music off a memory card and a wireless doorbell that made a boring old doorbell sound. He’s new to arduino and the tutorials for these modules are fairly vague, so I thought this would be a good opportunity to write up a tutorial on using an Atmega328 and a JQ6500 to trigger sounds with a really simple program.

From left to right: UART serial programmer, ATMEGA328P, JQ6500 MP3 module, microSD module, and 2 channel amplifier

Here’s the tools we had, a really neat set of stackable modules called Microduino programmable with the standard Arduino IDE (though you might not know that by reading their website — for this ATmega328 at 5V and 16Mhz clock, you can tell the IDE that it’s an UNO, no extra hardware files are requried.)

While I used these modules to get this project to work, if you get these parts in a different format (maybe an Arduino UNO and a JQ6500 on a breakout board) the following instructions should be relevant to you, too.

So we’ll deal with two stacks separately first: the audio module with the usb port stacked on top of the memory card module and the ATmega328 stacked on the UART.

When you plug in the audio + memory card stack, two drives will show up on your PC: one is the internal storage on the MP3 decoder, you probably don’t want to touch that one. But the drive that shows up called “SD” is where we can drop our MP3s. Microduino’s wiki has some information on the necessary naming scheme: Our file will be called “001.mp3” and be placed in a folder simply named “01”

Audacity makes it easy to grab a short clip of our chosen sound: a nice piano arpeggio from a longer song. If you’ve never used Audacity, no problem, you can visit their website for a Mac or Windows executable, or if you’re on debian (ubuntu / kubuntu / mint etc) you can just open a shell and type “sudo apt-get install audacity” and it will magically be installed on your OS. File → Open your song, click and drag across its sound wave to select a portion of it, and hit play to listen to your selection. Once you’ve selected the few seconds you want to play, you can hit File → Export Selected Audio and choose your file type as MP3, save it with the filename ‘001.mp3’

With your mp3 moved to the ‘01’ directory of the SD card, we can unplug that module and start programming our ATmega328. The microduino wiki was really vague on how to write code to control the MP3 module, but thankfully it gives the model number of the IC it uses: JQ6500. So I searched for a “JQ6500 arduino library” and found something really well documented here. So download that library and add it to the arduino IDE in the usual way (Sketch →Import Library →Add Library… or unzipping into your sketchbook, whatever works for you.) Check out the example sketches, “Full Demo” and “HelloWorld”, but here’s my code to simply play the first file on bootup. (01/001.mp3)

The only part that may be different based on your hardware is line 5, the object declaration that defines what Arduino pins will communicate via software serial to the JQ6500 chip. Looking close on the underside of this particular breakout board, the default TX and RX serial pins (the ones not in parentheses) are labeled next to D2 and D3, which in Arduino IDE language corresponds simply to 2 and 3.

So I declared my object as mp3(2,3) but if you’re using a different breakout board for the JQ6500 you will have to determine which 2 pins are wired to JQ6500’s RX and TX and use those pin numbers in your “JQ6500_Serial mp3(tx, rx)” declaration. By the way, ‘mp3’ is a user definable name, it can be called whatever you want.

Once you’ve got that figured out, you can load the code to the little stack of UART + ATmega. Unplug it once it uploads, and join the two stacks together, and add the amplifier module on that, so you have a whole tower of modules. Oh, important thing to know at this point: if you try to power the stack via the audio module’s USB, it won’t work, it will try to boot into file transfer mode, so power it with the UART module or otherwise.

If everything has gone right so far, you can plug a little speaker (the aluminum 3W style pictured at the top is perfect and easy to get a hold of) into the amplifier and give it power you’ll hear your sample. Did it work for you? I hope so.

To get the sound to play only when our original doorbell rings, we have to add a conditional to our program: instead of just in the setup, we use an if statement in our loop so that the ATMega328 is constantly checking for an input, it’ll look something like this:

void loop(){
if(AnalogRead(A0) > 400){;

Our input will be the two wires that use to be the doorbell’s speaker. For this, I cut off the original speaker and soldered new wires into its place. One of these wires should just be grounded, and the other wire can be stuck into A0 for measuring.

To make a sound, the speaker is pushed and pulled by changes in voltage. ATmegas have a 10-bit analog-to-digital converter that is super useful for measuring changes in voltage. Instead of measuring if something is turned on or off (like a button, which is strictly on or off, digital, 1 or 0) the A0-A7 pins let you measure subtler changes like a speaker buzzing around in between high and low voltage (between 1 and 0 😉

The readAnalog function performs this measurement for us, and if you want to experiment with this you should try the File → Examples → Basics → AnalogReadSerial program, which lets you open the serial monitor and see what voltage the ATmega328 is measuring. When you have what-use-to-be-a-speaker wired to GND and A0, and watching your serial monitor when you ring the doorbell, you’ll see a number jump around and settle back to 0 once the doorbell stops ringing. So in the code snippet, our mp3 will be triggered whenever the voltage jumps above 0V. (the 400 is a number we pick. In arduino-land, zero volts reads as 0, and 5 volts reads as 1023. That’s just because the hardware on the chip has 10bit precision, which is to say, it can distinguish between 2¹⁰ different voltages. 2 to the tenth power equals 1024, and if you have 1024 numbers and want to start at 0, you get the range 0–1023. So any voltage it measures is returned as some number between 0 and 1023.)

However, this simple way of waiting for change in voltage is susceptible to a electronic hobbyist’s worse nightmare: noise. Even if things are wired correctly (but especially if they’re wired loosely) little spikes in charge from humans handling things or other more mysterious sources can cause a spike in measurement, thereby triggering our doorbell when no one is at the door.

A slightly more reliable way to wait for changes in voltage, then, is to use a handy feature of ATmegas called an ‘internal pullup resistor.’ This phrase didn’t make sense to me for a long time so I’ll elaborate a little: if there’s a signal that may naturally fluctuate and you want to prevent it from fluctuating, you can wire a resistor in between that signal and a power source (thereby “pulling the signal high”, making it a “pull up resistor”) or wire a resistor in between the signal and a ground source (thereby “pulling the signal down to ground” making it a “pull down resistor”). If I didn’t explain it well enough, search for more articles about it, it’s a super useful thing to understand.

ATmegas have one of these resistors built in inside the chip and it can be programmed to be connected to a power source or not (this is the magic of programmable computers…they are machines that re-wire themselves). It can keep the analogRead measurement pinned to 1023 until some other active component, like our speaker signal, interferes and pulls the voltage low (remember how the speaker gets voltage pushed and pulled? That’s why this can work by measuring from 0V or from 5V, we just want to wait for a change in voltage, doesn’t matter what direction.) So to set that internal pullup resistor and wait for a change away from 5V, our code will look like this:

Oh, and the pinMode(6, OUTPUT) and digitalWrite(6, LOW) is kind of silly, I’m giving myself an extra place on my tiny MicroDuino modules to ground the speaker. Arduino UNOs have 3 different places to GND things, but if you ever need more, you can set a pin low and it will work just the same as a GND pin. Just don’t ground something that uses lots of power, because this forces current to go through the chip.

But that’s the final program, and the final necessary wiring: old speaker pins plugged into GND and A0, JQ6500 connected to pins 2 and 3, and I’m using the 5V pin to power the doorbell. It use to be powered by 220V mains, but that part exploded for reasons I don’t need to go into detail about here. Did you ever see Wayne’s World? Fireworks. Suffice to say, this almost become a blog about how to build a replacement full wave rectifier out of diodes until it occurred to me that the parts that I want to use can be powered off 5V.

Now when the doorbell makes a sound, it triggers the arduino to command the JQ6500 to play its mp3 and we hear a nice piano arpeggio instead of a boring old simulation of a doorbell.

Xin Che Jian in Shanghai

“New World Shopping Center”

Shanghai has always had a place in my imagination, from some mixture of movies and cartoons. “I think maybe because of Jackie Chan?” “Jackie Chan?! Jackie Chan is from Hong Kong!” “Yeah but some of his movies are in Shanghai probably, right?” So yeah I don’t know why, but I’ve always wanted to come here, and since the hacker-tour-group was moving onto Beijing the day after I arrived, I decided to stick it out with some new friends at Xin Che Jian.

It is an extremely active and welcoming community at Xin Che Jian: within hours of ■■■■■ getting in touch via IRC, we were let into the space and shown around. A couple hours after that, ■■■■■ got a commission to work on the space’s security features (name redacted due to maybe-his-visa-doesn’t-allow-commissions). So the members there are always looking for ways to improve the space and come up with new workshops: I hear they do workshops every weekend bringing in dozens of kids or adults— workshops every week is AMAZING for an ad-hoc organized community group.

They are tucked in a co-working space among design studios and probably tech-consulting firms (Wild guess, maybe I’ll ask next time I’m there). The kind of office where all the walls are made of glass and people seem to do business without a scrap of paper. There’s a nice hydroponics setup with a fat tilapia fish named Henry. There’s water-jugs converted to RGB LED lanterns hanging from the ceiling. Actually now that I look up at the ceiling I see all kinds of things hanging up: an RC helicopter, a model fighter plane, a bag of large sheets of styrofoam, and the wooden frame of an ultimaker 3D printer (lol). It reminds me of Makerspace Urbana, really, just big tables to spread out, and lots of boxes of old projects residing on shelves. Also you have to walk through a backalley to get in and you’re not sure if you’re in the right place until you see gears and LED strips.

Shanghai is an incredible place to have a hackerspace. Head east on Beijing road to the electronics markets: outdoor stalls in addition to a multi-story mall dedicated to selling electronics components. You can point to the one you want, haggle a price, head back to your hackerspace to see if it works, and come back and buy 1,000 of them if you want. My friend and I recalled all the times a project was slowed down to wait 2 weeks for a part (always faced with the dilemma, get it in 2 days, or get it cheap, I had the realization yesterday that all those parts I buy off eBay are available at the Chinese price, but I can get it today. Cause I’m in China. Mind blown.)

Linear rails, articulated arms, and motor couples, oh my!

Some test pieces for interactive fabric

Those are LEDs on DIY circuitboards weaved into a patch of cotton. The hand loom it was made on was laser cut, gifted to me by Walter Gonzales of Fab Lab Lima (Thanks, Walter!). Stainless Steel is used as a warp thread and can provide power to light up the LEDs, controlling each row individually.

The cooler part is that with Arduino, you can write a program that switches these threads from output to input very quickly. This means that each thread can act as a touch sensor (Like the Celestial Celeste) but if touch is detected, electricity can immediately be output down the same thread.

I’ve got a video of plain steel thread acting as a touch sensor (this is the Makey Makey method of using a large pull-up resistor and detecting when the sensor pin becomes grounded via your skin).

Unfortunately, I didn’t use LEDs with built in resistors (like the Adafruit sewable LEDs) so I can’t power them with 5V directly. Long story short, the detection circuit becomes more complicated if I have to use resistors before the output. Another option I’ve yet to try is detecting and powering the LEDs with an Arduino running at 3.3V (like the Adafruit Floras).

10/11/15 Update: Got it blinking with a Flora. Will probably have to mill my own board to integrate the resistors needed to sense touch and power LEDs. Or I could probably solder megaohm resistors to these same LEDs boards and weave them in…