Monthly Archives: August 2018

Enginursday: Prototype Capacitive Touch Dance Floor with a Teensy and XBees

via SparkFun: Commerce Blog

I’ve always wanted to build an interactive dance floor. After hearing about the capacitive touch pins available on the Teensy from Joel, I decided to try it out on a prototype made out of cardboard. While it is not the most durable floor, it was sufficient enough. I also added a pair of XBee Serial 1's configured for I/O line passing to make it simple for controlling something at a distance.

Prototype Capacitive Touch Dance Floor with Teensy and Wireless XBees Set for Line Passing

To test, I had my crewmate Julio come in from Block 1750. Every summer, we go out and fundraise by dancing in Boulder for a few events such as Block 1750’s Block Party. It takes a lot of work to fundraise and every dollar counts so for the finale, we usually have Julio hand hop for every dollar donated. I set up a counter with a 7-segment display to keep track of the number of hand hops and to see if the capacitive touch tile was reacting as expected. To verify that it is working, I had some people counting the hops at the same time. Check out the project demo below.

Results from stress testing the Teensy's capacitive touch sensing pins

While it seemed like a straightforward build, I had some interesting results from stress testing the Teensy's built-in capacitive touch pins. The sensitivity varied depending on the setup or environment. This required a few adjustments to get it working but it was not the most reliable. I would have to constantly tweak the sensitivity or set-up to get it working.

Power supply

The Teensy's capacitive touch pins read differently depending on the power supply. Switching from a wall adapter to a LiPo battery for remote power was enough to cause the Teensy to not react as expected. The Teensy was able to detect a touch by touching the LiPo battery and copper electrode. Adding a piece of copper under the cardboard floor with a wire leading to the battery for reference seemed to help.

Copper Tape and Wire Underneath the Tile for Reference

Differences in material and location

After testing the tile on different floors, I noticed that the tile would not react the same on each. The sensitivity with the tile and battery on carpet was not the same when testing it on concrete. With the wire touching the battery for reference, the Teensy had a false trigger when no one was directly touching the electrode. By keeping the same sensitivity, I had to add a piece of carpet under the tile and disconnect the wire from the battery. The sensitivity changed once again when placing it over a wooden floor. The tile also had false triggers when testing it out on the same type of floor around the building (i.e. first floor to second floor and different rooms).

Tile on Carpet Tile On Concrete Tile on Wood
Carpet Concrete Wood

Direct contact vs. proximity

Another characteristic of capacitive touch sensing is the ability to detect something even when the object is not directly touching the electrode. The sensitivity of the Teensy's capacitive touch pin was set just enough to detect a hand even though it was not touching. This was not ideal when my friend was hopping on his hand. The Teensy would still detect my friend even if he was above the electrode.

Teensy Detecting an Object when Not Directly Touching The Electrode

Making it better

If I were to continue using the Teensy's built-in capacitive touch pins for the interactive dance floor, I would try to:

  • Utilize more of the capacitive touch pins that are available instead of just one small tile for a wider area.
  • Add the TeensyView OLED or use the serial pass-through with the XBee’s UART pins to help adjust the sensitivity.
  • Use a more durable floor material instead of a flimsy piece of cardboard.
  • Seal the capacitive touch material to prevent the electrodes from damage.
  • Make the copper electrode bigger.
  • Add rubber pads below the tile to prevent sliding when a person is moving over the floor.
  • Place the electronics in an enclosure for protection.

Resources and going further

If you are interested in the circuit and example code used for the prototype, check out the GitHub repository.

Capacitive Touch Dance Floor with Teensy

That’s all for now. Until next time!

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DIY Nixie Tube Clock Build

via SparkFun: Commerce Blog

I’ve always liked the look of a Nixie Tube Clock. They are Cold War-era clocks (now seen as steampunk) with metal coils in glass casings. I decided I wanted to build one, but the pieces were harder to find than I anticipated. SparkFun doesn’t carry the boards or kits and it seems they’re only found in Eastern Europe on eBay. The glass tubes themselves are not being produced anywhere that I could find, so the only ones available were used from a seller in the Ukraine also off eBay.

I wanted the base of my clock to be different, not a wooden or 3D-printed box, but something with gauges and knobs. I continued my eBay search and found an old CB radio tester from JCPenny for pretty cheap. I can’t find a date anywhere on this thing or on the internet, so if you happen to know, I am curious.

I made my eBay purchases and all the pieces made it to Colorado without any problems. The board fit quite nicely to the CB Radio Tester so we were off to a great start. I didn’t realize how many pieces really were involved, so this quick soldering job became a three-day build since I never had the time to do it all in one sitting and ran into a few problems.

CB Radio Tester

nixie tube

board on base

In the video, you can see that I ran into more than one problem. I am SparkFun’s video producer, so I have no engineering experience and this was really the first board I had ever soldered. A lot of this project was blindly following along with the hookup guide, with poorly lit pictures, and just hoping things would work out.

Generally, they did. I put a few resistors in the wrong place, but luckily Feldi caught that before I powered it up, so I learned the excruciating process of desoldering resistors and fixed the problem.

Next was soldering the actual nixie tubes to the board. This process made me want to throw it at a wall because the wires were never long enough to comfortably attach each tube. I spent so much time meticulously placing each wire from each tube in to solder with tweezers. I am not the most patient individual, so this process was more of a learning experience for me than anything in the build. If you choose to build one, I’d recommend getting some extra hands to hold them in place to solder. Six were soldered, but one is a little crooked and it will forever annoy me.

I got some help from a few other employees to teach me how to dremel out a rectangle in the metal base of the CB Radio Tester. No surprise – I messed that up the first time and didn’t make it large enough to fit the tubes, so it was back to the machine shop for more dremeling and filing, and finally everything fit together. I literally did a backflip in celebration (check the bloopers at the end of the video).

It’s not perfect, but I like to think it looks original and I am just happy I was able to build it. The hookup guide says it works on a 5V power supply, however the tubes don’t light up with their demo code unless it’s powered by a 9V. So I am constantly afraid it will explode at any moment when it is powered. To people who know how electronics work, I understand that this might be an irrational fear, but you should see my soldering job. Yeah, that thing will explode eventually.

This is where I am at in this build. Four of six tubes will cycle through the demo code; I’m unsure if that is intentional, and will find out once I upload the code to actually connect to the WiFi and work like a real clock. Four out of six is a win in my book, for someone who has never built a kit with Cold War-era parts.

the final project

Nixie Tube Clocks are known to not last very long when powered, so I might just keep it as a novelty on my desk and turn it on if someone asks about it during a tour or something. It was strange filming myself for this and trying to build something from scratch, but everyone was happy to help when I needed it and that was really cool to have during this process.

For now, check out the video, watch more videos on our YouTube channel so it looks like I am doing my job, and forever hope this clock won’t blow up and burn down SparkFun.

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Desk of an Engineer: the Owen Edition

via SparkFun: Commerce Blog

We’re back with more desk details! This is a series where we barge in on our engineers while they’re working and kick them out so we can document their desks in all their chaotic glory. And because we know that just isn’t enough information, we ransom their offices back to them in exchange for some details on what they have on their desks and why. We do this for you!

Clicking the image will enlarge it, so you can experience the full resolution of each engineer’s home away from home.

Today we’ve inconvenienced Owen, one of SparkX’s engineers! Let’s get into it.


Something unique about my desk is its location. Upstairs, the engineers generally have their own offices adjacent to a shared space, but here in SparkX we are always in the shared space. I’ve found it to be pretty nice to be able to shout in a particular direction depending on what kind of advice I need. And of course if I need to focus undisturbed I’ll just pop in some earphones. Yup, this beats working in a cubicle!

Alright now let’s get down to business and talk about the WYSIWYG desk. There’s no drawers on this bad boy, so my whole existence at SparkFun is laid out before your eyes. I’ll go into more detail moving from left to right.

Computer, cats, and capture

Right now I am setting up to test a new SPI-based sensor. I always start development using the SparkFun BlackBoard for a couple reasons. First, the ATmega328 is the backbone of Arduino and usually the first microcontroller that a beginner will use, so products need special permission not to run on the Uno. Another reason I like the BlackBoard is because we do a lot of development of Qwiic products, and the built-in connector simplifies my life.

When things get weird, my next go-to is a digital logic analyzer like the Saleae Logic 4 in the picture. Usually sensors and modules work the way they are advertised and the failures exist in the interface between them and the controller board. A DLA is like my own X-ray vision for electronics that helps me spot errors on the lowest level. In the upper left corner you can also see the box of microcontrollers that I use in special circumstances. One such use is to recreate GitHub issues and see if I can find a solution. The box includes both an ESP32 and ESP8266, a Teensy3.6 and a SAMD21 Dev board.

Another interesting item is the “Crazy Kitty Game” on the left-hand side of my desk. It’s a nine-card puzzle with an amusing print on top. Nate wrote a program to solve these puzzles, then challenged the rest of us to do the same. The goal is to share all the different methods we come up with so that we can see alternate ways to approach the problem. So far we’ve seen some brute force methods and an intuitive, Eagle-like, rat’s nest GUI, but I haven’t gotten around to trying my physics-based solution nightmare.

Sunglasses and OLED

Not much to see here folks. Its basically the no-mans-land between where I work and where I store tools/parts. In case you think I am sloppy for leaving my solder out I assure you I did that on purpose, cause my arms can’t quite reach my box of tools from a comfortable sitting position! I always keep a pair of sunglasses handy in case George Clinton ever drops by cause, ya know, that’s the law around here. You got to wear your sunglasses so you can feel cool.

Tools, parts, and doodads

Oh man, this is the part of my desk that I battle with the most. When the stacks get too high they spill over into my working area and it drives me batty. In fact this is a pretty neat day for me.

Working in SparkX is a really cool experience because we get our hands in nearly every process of product development. I’ll be contacting suppliers in China one moment and then turn to my right and build the first 50 units of a new product. That’s exactly what I will do with that big pile of parts as soon as I can prove that the hardware works as expected. Easier said than done!

This side of the desk is also where I keep my tools. For the time being it’s a pretty basic set but they get the job done. The turbocharged hair dryer and the Hakko soldering iron are great for melting things, including but not limited to my hair. I’ve also got a pile of resistors, jumper wires and small hand tools. One of my favorite items lately has been the bottle of flux that Seth from production gave us – its a real lifesaver when an IC comes out of the oven crooked.

Finally I’ve got my notepads - whether I’m in a board review and need to keep track of all the changes or I am designing software and need to visualize how the data is stored having a quick way to jot things down is essential.

Well, that’s all folks!

Thanks Owen! You’ve earned your desk back.

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Helen’s hoglet: an adorable adventure

via Raspberry Pi

Today is a bank holiday here in England, as well as for lucky people in Wales and Northern Ireland. Pi Towers UK is running on a skeleton crew of Babbage Bear, several automated Raspberry Pis, and Noel Fielding, who lives behind the red door we never open.

So, as a gift for you all while we’re busy doing bank holiday things, here’s a video that Helen Lynn just recorded of one of the baby hedgehogs who live in her garden.

Helen’s hoglet

Uploaded by Raspberry Pi on 2018-08-24.

You’re welcome. See you tomorrow!

The post Helen’s hoglet: an adorable adventure appeared first on Raspberry Pi.

How to Build a Combat Robot

via SparkFun: Commerce Blog

Hello everyone, it’s Robert. Today I’m going to talk to you about AVC and what it takes to build a combat robot!

SparkFun’s 10th AVC is coming up in just a couple weeks and I’m personally pretty excited. I’ve been involved in the majority of the competitions, either in my time as head judge or, more recently, as a competitor. Having seen both sides of the event, I can say that a considerable amount of effort goes into both! Coordinating and running the event requires a large amount of time and resources, and the same can be said about competing as well. However, building combat robots has been one of the most challenging, frustrating, yet rewarding things I’ve ever done.

Version 1 of Crippling Depression without armor panels

Version 1 of Crippling Depression without armor panels

What exactly are combat robots? First off, combat robots aren’t really technically robots. They’re really just armored remote-controlled vehicles that usually have a weapon. Strictly speaking, robots have some level of autonomy, which most combat robots do not.

There are many weight classes of combat robots, ranging from the insect classes (one pound - Antweight, three pounds - Beetleweight) to the intermediate sizes (12 pounds - Hobbyweight, 30 pounds - Featherweight) and finally the largest classes (60 pounds - Lightweight, 120 pounds - Middleweight and 220 pounds - Heavyweight). There are numerous other classes all the way down to 150 grams and up to 320 pounds, but these classes have fewer (if any) competitions.

Featherweight Rumble, AVC 2017

Featherweight Rumble, AVC 2017

Generally speaking, the goal is to have two robots enter an arena and knock against each other for two to three minutes until someone either taps out or their robot stops working. There are, of course, many restrictions as to the type of weapons that can be used, weight and size limits, etc. If you want to know more about the rules, check the website; it has a set of standardized rules that SparkFun’s AVC and other competitions use.

But ultimately, most fights involve attempting to disable your opponent by either pushing them, flipping them or using a spinning weapon to store (and transfer) kinetic energy. Of all the methods, I greatly prefer the latter.

The underside of Crippling Depression - the 7.25-pound weapon reaches 6K RPM

The underside of Crippling Depression - the 7.25-pound weapon reaches 6K RPM

At their core, combat robots are really just a couple motors for drive, a battery, an RC receiver, some wires, a frame to hold it all together and then (optionally) another motor or two to power the weapon. It seems simple, but it’s anything but. All the components that go into these systems need to operate under extremely harsh conditions. Even though matches are only two to three minutes in length, a lot can happen in that amount of time. This means material selection and optimization play a very important role.

For my 30-pound (featherweight) combat robot, Crippling Depression, I am using a whole host of materials including carbon fiber, various grades of aluminum (6061, 7075 and 2024), grade-5 titanium, S7 impact-resistant steel, UHMW-PE and carbon-fiber reinforced nylon. One of the greatest aspects of designing and building a combat robot is seeing components and materials pushed to their absolute limits.

Crippling Depression deconstructed, post-competition

Crippling Depression deconstructed, post-competition

To understand the forces involved, we need to talk a little about kinetic energy (KE) and Joules. Here’s a quick physics refresher: kinetic energy is energy that a mass possesses while in motion. An apple sitting on a branch on a tree has stored energy (potential energy), but as it falls and gains momentum, it stores kinetic energy (KE). When it falls and hits the ground, that energy is transferred into the apple and the ground. Assuming an apple weighs around 100 grams and falls from three meters, you could assume that the force when landing is equal to about three Joules worth of energy. Got it?

So just how much kinetic energy does a combat robot have? Well, it depends on the design and the weight class, but 150 Joules per pound is a good rule of thumb. So, a little one-pound (Antweight) combat robot could have a spinning mass that stores 150 Joules worth of energy, which is roughly equivalent to 50 apples falling from three meters. This is roughly the same as a bowling ball falling from the same height, which could easily break some bones and cause serious damage to a person.

If we start moving up to larger weight classes, the amount of energy starts to get pretty scary. I have several weapon options for Crippling Depression, and the most powerful weapon can generate just over eight KJ worth of KE. This assumes the weapon is spinning at full speed and would come to a full stop and impart all that energy into the opponent, which is admittedly pretty rare. However, to give some perspective to this number, a 357 magnum at close range packs around 672 Joules, and a 12-gauge shotgun packs around 4.4 KJ.

The largest combat robots have KE numbers exceeding 100 KJ, which is similar to the forces involved in a head-on car crash. This is why the arenas use steel floor panels and bulletproof Lexan walls. Many robots even use AR400 or AR500 armor plating, which is commonly used in armored vehicles and bullet-proof body armor. The amount of energy that combat robots can generate is downright terrifying.

It only takes a few seconds to mangle ⅝-inch-thick aluminum panels

It only takes a few seconds to mangle ⅝-inch-thick aluminum panels.

With the amount of energy involved in such small machines, things tend to break in surprising ways. Magnets explode out of the motor housings, insulation melts away from wires, components desolder from PCBs, bolts shear and solid metal plates easily twist and bend into unrecognizable shapes all in a matter of seconds.

With the vast variety of designs (flipper, vertical spinner, horizontal spinner, saw bot, clamp bot, under-cutter, mid-cutter, etc.), you need to constantly innovate and iterate your design to match your opponents: bigger weapons, more powerful motors, stronger armor, faster driver, etc. There is no perfect design. The most powerful vertical spinner can be easily stopped by a simple wedge, a wedge can be rendered useless by wedgelets, wedgelets can be ripped off with a powerful horizontal spinner and that horizontal spinner can be stopped cold in its tracks by a vertical spinner or flipper. It’s a game of paper-rock-scissors, but with a lot more shrapnel, sparks and burnt electronics.

The evolution of the internal frame rail for Crippling Depression.

The evolution of the internal frame rail for Crippling Depression. Iteration is life.

If it was easy, it wouldn’t be fun. I’ve spent the last few months rebuilding Crippling Depression from the ground up. I’ve replaced aluminum with titanium, shaved weight in some places to add it into others and changed around the geometry to make it harder to hit while making it easier to hit others. I know this is what everyone else has been doing as well, so I just need to cross my fingers and hope for the best.

The next installment of Crippling Depression, ready to cripple and depress

The next installment of Crippling Depression, ready to cripple and depress

If you want to learn more about Crippling Depression, you can check out my YouTube playlist for a build log and fight recap from the last two events.

The sport of combat robots is a great way to learn how to build something that needs to operate under extreme conditions. It’s recommended to start with the one-pound Antweight class to get an idea of how everything works and then move up from there. There are great tutorials that can be found on Sparc.Tools, my YouTube channel, and Arizona Robot Combat.

The best way to get started is to find a event and attend as a spectator. Thankfully, in just a couple weeks is the second-largest combat robot event in the US! Be sure to tune in and watch Crippling Depression and all the other robots compete.

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Friday Product Post: PaPiRus & GoPiGo!

via SparkFun: Commerce Blog

This week we have even more new parts and kits for your Raspberry Pi, including two different HATs from PaPiRus, as well as two versions of robotics kits from GoPiGo. If the RPi isn’t your thing that’s okay – we also have a huge 64x64 RGB LED matrix for you!

As a reminder, our Liquidation Sale is currently in full force! We’ve slashed the prices on these items to their lowest ever. Take a look and see if you can find a bit of treasure; the sale runs until 8/31!

Papyrus is an underrated font… just saying…

PaPiRus ePaper / eInk Screen HAT for Raspberry Pi

PaPiRus ePaper / eInk Screen HAT for Raspberry Pi

PaPiRus ePaper / eInk Screen HAT for Pi Zero

PaPiRus ePaper / eInk Screen HAT for Pi Zero


The PaPiRus is a HAT for the Raspberry Pi and Pi Zero that is capable of driving an ePaper display by making use of the existing open source RePaper codebase and examples. ePaper/eInk is a display technology that mimics the appearance of ink on paper. Unlike conventional displays, ePaper reflects light just like ordinary paper and is capable of holding text and images indefinitely, even without electricity.

GoPiGo Beginner Starter Kit

GoPiGo Beginner Starter Kit

GoPiGo Beginner Classroom Kit

GoPiGo Beginner Classroom Kit


The GoPiGo Beginner Starter Kit from Dexter Industries is a complete robotics kit controlled by the Raspberry Pi 3 B+. The GoPiGo works at your level, whether you are a parent looking for a smart, fun weekend project to do with your kid; a teacher looking for a way to increase engagement in your science course; or a grad student in need of a platform for robotics research that requires mobility! Assembly only takes about 30 minutes, which means you will be able to start using your new robot platform almost immediately after receiving it. This kit is also available as a classroom pack for up to five students.

RGB LED Matrix Panel - 64x64

RGB LED Matrix Panel - 64x64


Are you looking to add a lot of color to your project? These 64x64 RGB LED panels are an awesome place to start – that’s 4,096 LEDs on a 7.5 x 7.5" board! You can create animations, games and all sorts of other fun displays with them. On top of all that, thanks to an IDC connector and a seamless frame, these panels can be daisy-chained together to form even bigger LED displays.

Alright everyone, that’s it for this week! As always, we can’t wait to see what you make! Shoot us a tweet @sparkfun, or let us know on Instagram or Facebook. We’d love to see what projects you’ve made!

We’ll be back next week with even more fantastic new products!

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