Low Cost Foor Mat Switch

One of the biggest problems with having a lot of props, is the need to trigger them. Store bought props usually come with cheap photo sensors that never really work well. PIR sensors work pretty well if you can shield them from excess sources of IR, like direct sunlight. A third option, one that tends to be quite expensive, is the use of a floor mat switch.

Floor mat switches are at their simplest form to conductive materials arranged in some manner to allow the conductive components to remain separated until weight is applied. (Someone steps on them) While the weight is applied, the conductive components make contact and complete the circuit. After the weight is removed, the contacts again separate and break the circuit. This makes for a pretty reliable guest sensor, as the mat is not affected by sources IR and false triggering is pretty unlikely.

As I mentioned before, the biggest drawback to the mat switch, is the cost. Most mat switches are designed for use in industrial equipment for safety purposes, and are therefore rated for heavy usage. One night a year doesn’t seem to justify the ~$200 expense. One day as I was leaving the movies I saw a group of kids playing Dance Dance Revolution (DDR), and it hit me. There are tons of copies of DDR out there, and there are millions of cheep imported mats to work with your home entertainment system. A quick search of ebay found 2 Chinese import lower quality mats for $20. At $10 a piece, thats MUCH MORE suitable for a one day a year use.

Controller guts
Controller guts

Hacking the mat turned out to be a pretty simple task, as I had expected. The controller electronics are located in a black box at the top of the mat. Opening the box, on the model of mat I purchased was as simple as unscrewing 6 screws on the back side. From there I was able to get a good look inside the mat. The low cost DDR mat, is at its heart two sheets of thin plastic, with carbon traces printed on them, separated by a thin sheet of foam similar to that used in packing fragile materials. The foam layer is punched with numerous holes under each “button”. The bottom layer acts as a ground plane and when pressure is applied the foam compresses allowing the top and bottom layers to meet, making contact. This change in resistance is then fed to a specialty chip located on the PCB that converts the contact to a signal usable by the video game system. While it is certainly possible to decode that signal and use it without altering the mat it would add more expense and therefore not acceptable for this application.

For my needs I didn’t really need separate signals from the individual buttons. I just wanted the whole mat to act as a giant switch.

Bridging the Switches
Bridging the Switches

For a while I toyed with the idea of taking the columns of the mat individual switches giving me a way to detect direction but the mat is actually small enough that i decided that wouldn’t be to useful. I broke out the Multimeter and started mapping out the lines from the various switches on the mat. The board contained a row of 0.1uF disc capacitors likely used for denouncing the controller circuit. I was planning on doing debouncing in software so I removed the capacitors and used their solder pads to tie all of the switches together, this was accomplished by taking a small piece of bare copper wire and soldering it across all of the connections. The mats connections were split to two sides of the board so this actually required two pieces of bare wire, and a small jumper to connect them.

Once the individual switches on the mat were bridged I attached two of the original wires from the mat cable to the pads for the contact, one to the ground plane, and one to a trace leading to the now bridged contacts. I then took my multimeter and set it for continuity testing, and attached it to the other end of the cable. It immediately started behaving oddly. I decided this strange behavior has something to do with the controller chip still being in circuit. so, I took my razor knife and carefully cut all of the traces leading to the chip, without damaging the traces needed for and of the switches. ( Ok really, technically i accidentally nicked the ground lead and had to move my ground wire form its original location to another location, but as long as you are careful you wont run into that problem. 🙂 ) After disconnecting the chip, the multimeter returned to its expected behavior. With no pressure on the mat the mat read an open connection. Once I pt pressure on one of the pads, the continuity tester beeped, and resistance dropped to around 1500 – 600 ohms depending on the amount of pressure applied.

I then decided, while I had the mat open, and i had extra wires in the cable, I would add in an LED for future use. This was simple enough, I drilled a 5mm hole, pushed in the LED, and soldered two of the cable wires to the LED. I then closed up the box, and now have a low cost mat switch that can be attached to anything.

WARNING!!! DO NOT USE THIS SWITCH FOR HIGH CURRENT, OR HIGH VOLTAGE APPLICATIONS!!!

Use ideas:

  • Solder it in place of the Try Me button on a prop from a big box store. (Note: Some try me buttons also turn off the prop if they are pressed a second time, so a simple event timer circuit may be needed. Theres plenty of room in the mat switch control box to house this, by the way)
  • Input to a PROP-1 controller. (Sky’s the limit here folks. Remember, the resistance varies with the amount of pressure applied… so you might be able to use the POT command for some rally cool efects)
  • Use it to directly switch LED’s to light some gruesome scene. AGAIN NO DIRECT HIGH VOLTAGE / CURRENT APPLICATIONS
  • Hook it to a low voltage relay to power more power hungry applications.

Your mileage may vary, the author of this article is NOT responsible or any damage to property, personal injury, or any other problems that arise from using this hack.

If you like it, and it works for you, I’d love to know about it, send me an e-mail to john@wohlershome.net

L.E.D. Fun

What do you get when you combine 24 awg stranded 2 conductor wire with a resistor, and a high intensity L.E.D.?

You get a really awesome spotlight so small that it can be easily hidden in even the smallest tree beach and yet illuminate a scene plenty bright enought.

Tonight, I wired 5 of these. 2 blue, 2green, and 1 red. Tomorrow I hope to make the housing for them.

Nightmare? Premonition?

I had a very strange experience this morning. At 4:27 a.m. I awoke from what was an incredibly vivid dream. When I awoke I was still choking on smoke and could even taste it… The dream was so vivid… This is what I saw.

I found myself standing along side of my car at an airport I didn’t recognize. Strangly I was near the runway and the terminal or some hangar building, I didn’t get a good look. As I was standing there I became aware of a large jet prepairing to take off. At that my point of view shifted to a point in the air above the runway. I was then able to see another jet in parallel to the 1st jet, this jet was sitting as if waiting for clearance to take off. As the 1st jet taxied past this 2nd jet the 2nd jet exploded with a force so large that the explosion tore the 1st jet apart. Then the perception changed again and I was back on the ground, running from the debris. The tail section of one of the planes came tumbling towards me riding the front of the blast. It looked almost as if it were a pin wheel. The black cloud of smoke engulfed everything as the tail section crashed into the building behind me. As the collision occurred I could hear the screams and wailing of countless people. As the smoke engulfed me and I began choaking awake, I heard the disembodied voice of a television announcer discussing the horrific tragedy involving an Air France flight and… Then I was fully awake still choaking, still tasting the horrible fumesl. I turned on the lights and half expected the room to be full of smoke, but it wasn’t… Within seconds my sence of smell returned to normal and all was well. I laid there staring at the fan trying to make sence of what just happened.

Overreact much?

The past few days, since Thursday before stronghold really, I’ve had some sort of stomach thing. abdominal pain, blated feeling, etc…

I let it go for a few more days, and then when it kept getting worse, I went to the Dr. he said it was nothing to worry about, and gave me some pills…  As I was leaving work to head to the Dr. I decided to look up the common side effects of the allergy meds I’ve been on for the past month.  The most commonly reported side effect, matched my symptoms exact…  I mentioned it to the Dr. he didn’t think that was the problem.   The 1st few days the new meds didn’t seem to be making any difference, so I stopped the allergy meds.  I’m now improving, but since I wasn’t 100% by Monday the Dr. wanted to see me again, and so he drew a bunch of blood and we will see what the test results say.

My mother of course is overreacting and is sure I’m dying…

Sigh…

Thank you CBS

HAHAH!!

I was watching CBS tonight and at the top of the ten o’clock news, they asked people to weigh in on their thoughts about the governor.    I was already on the computer, so I figured, “Why not.”

I wrote: “He’s a crook. Can we please get some politicians in Illinois that are NOT criminals!”

At the end of the ten o’clock news, tehy aired 3 comments from viewers.  Mine was #2. 🙂