PING Platform

An Exploration in Physical Computing

Proof of Concept: Week 1

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This week was first and foremost about getting acclimated. We hadn’t ever hooked into the Phidgets Flex Platform. So, we did that. We also hadn’t had more than a single IR sensor to work with until this week. A new Phidgets interface kit and new sensors were graciously provided by Dr. Baker, so we were able to plug in two sensors at the same time.

We then began planning.

We planned some of the specifics of the software platform. I’m not going to get too much into detail there just yet. Suffice it to say, our goal is to make game development as easy as possible.

We also planned our testing setup for the hardware. Essentially, we needed a way to incrementally adjust sensor placement along a single axis, while still mounting both the sensor and the distance adapter. We came up with 4ft x 4in strips of peg board, blocks of wood with dowels projecting from their bottom and sensors mounted on their side. Confused? There will be pictures next week.

We put it all together, and…disaster!

We ran into our first major snag when we mounted the sensors, hooked everything together, and saw that the the sensor data was noticeably erratic. Our high precision IR sensors were all of a sudden not so high precision.

We realized that the sensors were interfering with each other.

I’m going to try to explain why. Now, this is based on some factual knowledge, some conjecture, and some observation. (If it turns out I’m a moron and way off base, and you’re an engineer for Sharp or something, please tell me. I hate living in ignorance.) So, the sensors have two main parts: an IR emitter and an IR receiver. The sensor is able to measure data by measuring the time it takes for an IR pulse from the emitter to bounce back to the reader. Our data was jittery because the emitted IR pulse from each sensor was reaching the reader of the opposite sensor.

The good news is that this was only happening when there was nothing in between the sensors. Like a hand. Well, we want hands there. In fact, we plan hands to be there a lot. That’s kind of the whole point.

So, how did we fix it?

Well, we haven’t completely fixed it yet. We have some ideas, though. First, by adjusting the sensors so that they aren’t at the exact same height, and by making sure the emitter of each sensor isn’t aimed directly at the receiver of the other, we can reduce the jitter somewhat. Also, we think that by limiting the vertical scope of the sensors with some kind of physical obstruction, we might be able to reduce it further. We are also investigating ways we might be able to filter the IR signals so that they each exist in slightly different parts of the IR spectrum. Finally, we realized that the jitter is a recognizable pattern, and we are confident that it can be filtered out in software. Hopefully, some combination of these solutions will result in an error free data source.

Goals for Week 2:

  • POC Hardware Rig v. 1.1: Vertical Sensor Adjustment
  • More Software Platform Dev
  • PINGOS interface research, mockups

Written by tonydewan

September 6th, 2008 at 8:04 pm

Posted in Proof of Concept

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