posts tagged with the keyword ‘exhibit’


Traffic Lights

I recently repaired the traffic and walk signals at BBCM. The system had been running on a PLC (Programmable Logic Controller) which failed, and rather than find the proprietary programming cable and find and install the PLC Windows software, I decided to just put an Arduino and relay control board in place.

Arduino and Relay Board

I had a Teensy++ 2.0 I had pulled from another exhibit during an upgrade, and an 8 channel relay board on hand. These relay boards come in different configurations from 1, 2, 4, 8, and even 16 relays. Since I really only needed 5 relays (and 5 pins) I could have used an ATtiny85, but I had the Teensy++ 2.0 readily available. The wiring is all done using female to female jumper wires.

Traffic Controller

I mounted everything to a piece of scrap MDF and added mounting holes to that, with the idea that we’d screw the whole thing directly into the wall. The relay board has mounting holes, but the Teensy does not. That’s probably my one complaint about the Teensy boards, is that mounting them isn’t always easy. My Teensy BOB has mounting holes, but for mounting this Teensy++ 2.0 I just used some 3M™ VHB™ tape. (The “VHB” stands for “Very High Bond”). And yes, there are a few 3D printed parts on there. At some point I should make a 3D printed holder/mount for a Teensy++ 2.0


I try to label things clearly. If I look at this thing in 6 months, or 2 years, or someone else has to look at it, I want it to be somewhat apparent what is what, so there’s not a lot of guesswork as to what is going on. I included a label with the name of the Arduino sketch, and I always like to label power supplies. Sometimes we use 5 volts, and sometimes 12 volts, and they typically have tiny hard to read type printed on the side of the power supply that you can’t see when it’s plugged in.

The one thing I should start to add to the labels is the URL of the wiki page where the thing is documented. (Next time I’ll do this.)

Controller Mounted

Here’s the controller mounted. It’s not pretty. We ended up re-using the mount that the PLC was in, rather than screwing it right into the wall. In my defense, we did this repair on the floor during open hours, and it’s mounted high on a wall behind a TV. Does it work? Yes… Is it awesome, no… but again, it totally works.

The wiring for the lights was all 12 VDC, not 110 VAC, so those thin gauge wires are fine. Also, they were labeled, which was handy. (Thanks previous person who worked on this and labeled things!)

Wiring Diagram

I try to create wiring diagrams for everything. I use Fritzing because it’s simple and awesome and open and free. I often don’t find the components I need, but you can always just use a note and some text.

Here’s the script/sequence for the lights:

  1. Green Light is ON
  2. Walk Light is ON
  3. Waiting 4 seconds…
  4. Walk Light is OFF
  5. Don’t Walk Light is BLINKING (for 5 seconds)
  6. Green Light is OFF
  7. Don’t Walk Light is ON
  8. Yellow Light is ON
  9. Waiting 4 seconds…
  10. Yellow Light is OFF
  11. Red Light is ON
  12. Waiting 6 seconds…
  13. Red Light is OFF
  14. Don’t Walk Light is OFF
  15. (Repeat sequence)

I wrote this up to figure out how to program things. I find it helpful to plan things out before I start writing the code.

At first I just talked through the light sequence with someone and we made some assumptions about how it worked. We were slightly wrong, which I discovered when I dug a bit deeper into traffic lights and walk signals. I read at least some of the (very long) Wikipedia page on Traffic Lights. I also hunted for other info, and found some on the Signals FAQ page on the Minnesota Department of Transportation web site. (As I mentioned with the 911 Phone I really do aim for an accurate and realistic experience with these things.)

It’s been a few weeks and the lights have been working fine. Hopefully that will continue to be the case. If something does stop working we’ll open a ticket for it so we have a record. And yes, we do use an issue tracker for our museum exhibits… doesn’t everyone?


911 Phone

What looks like an ordinary desk telephone is actually part of a museum exhibit at BBCM that lets kids practice dialing 911. When they pick up the receiver they hear a dial tone, and can then dial “911″ (which plays the proper DTMF tones) they then hear the line ringing, and then an operator answers and says “911, what is your emergency?”


Inside the phone I’ve replaced the guts with a Teensy 3.2 and Teensy Audio Adaptor board. This combination handles the phone receiver being lifted, the keypad being pressed, and the playing of audio.

Teensy Pins

After consulting the docs for the Teensy Audio Adaptor board I knew which pins were used for the adaptor board, and which I could use for the receiver switch and the keypad. From what I could tell 11 pins were available (0, 1, 2, 3, 4, 5, 8, 16, 17, 20, 21) and I needed seven for the keypad and one more for the receiver switch. Plenty of pins!

I chose to go with a (perhaps slightly odd) method of having some pins point up instead of down so that I could attache female jumper wires to them. I’m not 100% happy with this solution, but it worked for this.

Teensy Wiring

The female jumper wire headers are nearly as tall as the Teeny + Audio board combined. You can also see a potentiometer used for controlling the volume, and a 1/8″ audio jack which goes to the speaker in the handset.

Receiver switch

I re-used the existing receiver switch and wired it into the Teensy. The switch is NC (Normally Closed) instead of NO (Normally Open) so I just reversed the logic in the code when looking for the switch to trigger. When the receiver is lifted the dial tone sound plays. (Also, if you leave it off the hook too long, it will play the annoying off-hook tone. (I aim for realism with this stuff!)

Keypad back

The keypad was also re-purposed (once I figured out the wiring) and wires were soldered onto the tiny thin wires, and the heat shrink tubing was added. The keypad runs to a small piece of perfboard which is used to connect to the Teensy, along with a few resistors in the mix.

Keypad Notes

Notes on how to wire up the keypad. I originally used a SparkFun Keypad for testing and development before I had a (broken) phone to tear apart.

Fritzing Diagram

Here’s a quick wiring diagram showing how it’s all put together. (I try to match wire colors in diagrams with the real-world wire colors, at least before any maintenance/repairs happen.)

Connection Board

The connector board allows for easily removing the Teensy if that’s ever required, or replacing the keypad if it goes bad. It also adds in the resistors necessary for the keypad to function properly.

Magnet Mount

For mounting the Teensy into the phone I opted to use an old hard drive magnet with a piece of wood attached. The Teensy is screwed to the wood (which is a good insulator) and the magnet is also screwed to the piece of wood, and then attaches strongly to the steel base of the phone. (There’s also gaff tape on the base of the phone, as extra protection between electricity and metal surface.)

RJ9 Wiring

I found this diagram for the speaker wiring from the handset, and wired the appropriate lines to a 1/8″ audio plug that goes into the adaptor board.

One other thing I did was add code that only accepts “properly dialed/formatted” phone numbers. So if you pick up the receiver and dial “4738911″, you didn’t dial “911″. You need to hang up and try again, with a proper “911″. There’s a buffer that looks for 3 digits (or 7 digits) and if you can’t get that right, it doesn’t work. As I said, I aim for realism with these things…

(Note: I may have left in a few numbers from testing. I’ll have to ask Jenny or Hannibal for the details.)


Make it Move

I’m pleased to announce that for the second year I’ve had a piece selected for Body and Machine 2016: Kinetic and Interactive Art. This year my piece Click Whir Squee will be on display. (The show runs from April 2nd, 2016 to Aoril 23rd, 2016 at the Northrup King Building 3rd Floor Gallery in Minneapolis, Minnesota.)

Click Whir Squee

Since Click Whir Squee involves abusing a piece of hardware that is close to 20 years old, I can’t guarantee it will keep doing what it’s supposed to be doing for the entire run of the show. That’s part of the excitement of kinetic art… and it’s actually integral to the statement this piece makes.


I may try to dig up a few more of these TR-1 Minicartridges to swap in when the one in the machine gets destroyed. That might be enough to keep it running, but would rely on someone involved with the show doing maintenance. (Which I’m fine with.)


If you’ve already seen the video, you can just enjoy the photo of a cat that has been provided above. (It is called Body and Machine, after all.) Otherwise, here’s a video.

Make it Move


Big Keyboard

If you happened to see a post titled 8 Crazy Keyboards That Will Trick Out Your Typing over on the Make Blog, you may have seen the big keyboard I worked on last year.

It was for a graphic design station we built for “Word Headquarters” at the Betty Brinn Children’s Museum. (I did this project as a contractor, before I worked at the Exhibits Shop.) Here’s a bunch of images that show the building of the keyboard.

Concept #1

This is the concept Mike came up with, which was to use lots of different sized pieces of wood, CNC’d to look like letterpress type (though obviously not reversed, as they would be unreadable.) This was definitely a fun design, but things always change along the development path…



While Mike was working on a design, I mocked up a drawing showing the spacing I thought would work using arcade buttons and how close together we could get them. This helped determine the overall size of the keyboard. Things could obviously get more spaced out, but this was the tightest we could go.

Teensy++ 2.0

I’ve built plenty of keyboards over the years using Teensy development boards so there wasn’t too much new happening on that front. Still, it’s always good to breadboard things up for testing.

Concept #2

We ended up going with a simpler and cleaner key layout than the original concept. As you’ll see later, we added variations elsewhere in the piece.

Teensy++ 2.0

Did I mention the keyboard would have 46 keys? Well, 46 is the number of digital inputs you can get on a Teensy++ 2.0 board. That’s every single input. (And yes, there was an issue using pin 6 which eventually got solved.)


Here’s a big piece of HDPE that’s been milled out for all of the buttons. Yes, that’s a lot of buttons! (There are 47 buttons because we used two for the spacebar.)


Here’s the back of the big piece of HDPE. That’s a lot of wires! We used slip-on connectors rather than soldering wires to the buttons (for ease of maintenance) and the other ends of the wires all go to screw terminals.

Teensy++ 2.0

All wires run to screw terminals on an Adafruit Perma-Proto board. It’s not the cleanest thing, but the deadline was tight on this, and the impending launch date meant we had to get it all done and working, even if it wasn’t the prettiest under the hood. (And yes, this is mid-wiring… not everything is connected yet!)


More wiring, more wiring, labels for everything… And testing as we go.

More Wires!

Here’s the piece of Alupanel attached to the top of the HDPE. It also serves to hold the wood keys in place. Each key has a lip at the bottom to hold it captive and is held up by the spring in the arcade button. (At some point I did weight tests to determine a safe weight for each key so that it wouldn’t press down on the button too much.)

Wood Keys

Since we went with a uniform size for the keys, we added some variety in the choice of woods used. You may notice there is no return key. We eventually replaced the exclamation point with a return key. (We honestly didn’t think we’d need one due to the way the application allowed the use of text, but like all exhibits you put on the museum floor, things change over time as you learn how they are used.)

Wood Keys

I think the nice, clean, readable type turned out great. I’d still like to see the really varied version that was the first concept some day, but this works for now!

Wood Keys

There’s about 650 lines of code running on the Teensy, including code for handling the shift key with every key, so even though you don’t see the exclamation point anymore, you can get one by holding down shift and typing the number “1″ key. With the letters you get lower case and upper case, and with the numbers and other non-alpha keys you get whatever would normally show up with the shift key on a standard US keyboard.

In the end, this was an awesome project to be involved in. Thanks to Kathy, Mike, Sam, and Dom for contributing to the entire thing.


Video Installation

Last summer Ray Chi got in touch with me about an installation he was doing for the Milwaukee Art Museum. He wanted a video screen that could be activated to play a video by touching a metal plate. Well, actually six videos and six video screens and six metal plates.

I told him I’d figure out how to get it all to work the way he wanted. I came up with a few ideas, one of which was using Processing, which I did get working, but at the time Processing wasn’t really running on the Raspberry Pi, at least not officially (or very well) and since the Pi was what we ended up choosing, I needed another solution.

For an installation that’s going to be running for years, simplicity and reliability are key. I had used Pis in the past many times for video players using omxplayer. Typically I’d just launch omxplayer on boot and have it play a video, looping, forever. For this application we wanted the video to play only when the metal plate was touched by a human hand (and then stop playing when someone stopped touching it) which meant capacitive touch.

Rather than spend a lot of time coming up with something that might work, I went with something that I was 98% sure would work. I used Adafruit’s Standalone Momentary Capacitive Touch Sensor Breakout attached to a Teensy LC. Why a Teensy LC? Because it’s a low-cost (LC!) Arduino-compatible microcontroller and it can emulate a keyboard.

Yes, a keyboard! If you have a USB keyboard connected to a Raspberry Pi computer while omxplayer is playing a video, you can just hit the space bar to play the video, and then hit it again to pause the video. Those are the two things we needed to do.

Video Player Controls

So, Raspberry Pi, running omxplayer to play the video, with a Teensy LC attached programmed to work as a USB keyboard, and triggered by a capacitive touch sensor, which was then connected to the metal plate. Simple!

There was this issue of……. timing.

So in theory, the Teensy would just need to send a space character to play the video, and it would do this when you touched the metal plate. But! (And it’s a Big But) the issue was that we wanted the video to start playing at boot and then pause at the beginning and sit there waiting… for someone to touch the metal to start the video playing. Rather than fire up the video via the typical Linux methods, we ended up just starting up the Pis, auto-logging in, and having them wait at the command line… yes, just sit their waiting, doing nothing… Sort of.

When the Pi booted up, it provided power to the Teensy, which then started running its sketch. The sketch would start at boot, wait 45 seconds to ensure the Pi was booted up and sitting there waiting at the command line, and then it would type:

/bin/bash /boot/

So we actually used the Teensy to send the text to the Pi (just as if a human typed it) which then fired up the script and started the video playing. The sketch would then wait 2.4 seconds and type a space character, which would pause the video. This set the state of things exactly where we wanted them. The video way paused, just waiting for the next command from the Teensy, which was… space, of course!

Now, there’s the concept of “rising edge” and “falling edge” when it comes to pressing buttons. A rising edge is the transition from low to high, and a falling edge is the transition from high to low. That’s a fancy way of saying we can tell when the button is being pressed, and when it’s being released. It’s best to use debouncing for this, and there’s a library for that.

Video Players Mounted

So with everything mounted in place we still had to deal with one issue. The HDMI displays worked find as long as they were turned on before the Raspberry Pi computers. If they were turned on at the same time the resolution wouldn’t set right, and the video would be letter-boxed. There were two options, one would be using two different power strips to get power to everything, with instructions for museum staff to follow a specific order. This wasn’t ideal, so we went with option two. I used a time delay relay so that one single power strip could be turned on, which would turn on the HDMI displays, and then a few seconds later turn on the computers. It worked. (And yes, I found out later I probably could have fixed the issue in software. Duly noted.)

Are there things we could have done better? Yes. Did we get the project done on time, and within (or under) budget? Yes. Was it fun and challenging? Yes and Yes. You may read this and think “Hey, you totally could have solved problem X by doing Y!” and you’d probably be right. I’ve found a number of things I’d do slightly differently if I were to do something like this again. That’s all part of experience, and learning, and sharing… right?

Video Player

When the installation was all done and tested, I got photos of everything, and then set to work on documenting it all. I delivered a 14 page manual on the construction and operation of the video players, along with the code and instructions on how to use one of the backup SD cards that was prepared in case of failure.

Besides, now I can (sort of) say that my work is in the Milwaukee Art Museum. ;)

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