Our idea was to combine EL-Wire, heart-rate sensors and lasertag into a fun tactical action game. EL is short for electroluminescent wireand is pretty much just wire that glows when an AC current is applied through it. Lots of cool and trippy designs can be used with EL wire to create clothes, costumes, signs, displays and anything else that needs a visual representation.
The basic goal here was to create two suits that serve as laser tag outfits in a dark environment. The suits will be outfitted with heart rate sensors, EL wire and the laser tag electronic set ups. The wearer's heart rate will be detected by the appropriate sensors, which will then determine how much of the EL wires on the suit light up. A faster heart beat will cause more of the suit to light up, and vice versa. As a consequence the wearer will become more visible to the opponent and thus easier to target. The idea here is that the wearer's must keep their heartrates down if they are to remain covert.
The results of the project can be applied in several different aspects. The EL wire communicates visual information that the other person would otherwise not know without any other form of communication, in this case the wearer's heart beat and how excited/nervous the other person is. In practical applications, certain aspects of someone's health can be monitored with a similar suit without having to hook up a large machine to the wearer. Really, we just wanted to make a cool light up suit.
Our project consists of four basic components thrown together. On the suit, we have six infrared detectors that act as hit sensors. The firing mechanism consists of an infrared Led focused through a convex lens. This is mounted inside an arm-mounted PVC pipe "cannon". The third part of the project is a heart-rate sensor around the stomach. Finally, our suit has EL-wire sewn into the fabric. When one of the infrared sensors detects a hit, the EL-wire around the sensor lights up. Also, the EL-wire is supposed to light up with relation to the wearer's heart rate.
The EL wire was a fun thing to work with. Not only was it pretty to look at when lit, and not only did it make the project visually stunning, it presented an interesting engineering challenge. The main challenge when working with EL wire is that it operates off an AC voltage. The arduino, and most other digital components operate off of DC voltage. So combining these two circuitry elements in a safe and operable way was tough. Luckily, we were able to tap into the EL wire community for help.
We stumbled upon one really great operating solution. You can use a special chip that is commonly used in AC/DC circuitry pair-ups like ours. It is an opto-isolator chip. The basic idea is that you separate the two parts of your circuit and use light to make meaningful connections between the two. This opt-isolator uses a light transmitter and reciever so that the AC and DC elements are electrically isolated, but can still interact. You digitally flip on an led (DC elements), and then an optically-triggered TRIAC receives the light and activates (AC elements). You can see how we used this chip in our lasertag design. We use the arduino to digitally flip on and off one side of the opto-isolator. This in turn flips on and off distinct EL wires. Thus we are safely able to control when the EL wires light up, for how long, and in what patterns. The circuit schematic below shows a basic set-up. We used this design in two configurations. One with 8 opto-isolators, to control the EL wires assigned to display heart rate information. And one with 6 opto-isolators, to control the EL wires assigned to display a laser hit.
The IR sensor system is a simpler version of the laser tag gun systems that can be found here. We modified it a little in that everything was controlled by the Arduinos in the suit. Basically, we had a high power infrared LED (TSAL6100) mounted inside a PVC pipe of diameter 2 inches. The led was focused by a convex lens. To do this, we had to place the led at the focal point of the led. Our lens was a "PRECISION 38.1MM DIAMETER 101.6MM FL BI-CONVEX LENS" and we got it for 8$ from [Surplus Shed.] This setup increases the range of the led dramatically by focusing the light into a tight beam. Our gun had a range of about 150 meters.
We used the TSOP4840 chip as our infrared reciever. It was very simple and easy to use. Whenever the chip recieves a 40khz infrared signal its data pin goes from +5.0 v to +0 v. The only really tricky part about this setup is that we had to flicker the infrared led at 40khz in order to get the reciever to respond. Now, this would be easy to setup in the arduino's code with a couple delay functions, but we wanted didn't want to slow down our arduino so we decided to drive the led through PWM. To do this we hooked a transistor to pin 3 of the arduino and had it pulsing at 40khz. Now, the pwm pins on the arduino usually only pulse a a specific rate, so we had to do a little bit of hacking to get evrything working.
The code for the gun is below.
The sensor used to measure heart rate was a heart rate module for use with a Polar Heart Rate sensor, which can be bought from SparkFun. The basic idea behind this is that a user is wearing a Polar Heart Rate Sensor (which we bought separately from the manufacturer), which emits an electromagnetic pulse when a heart beat occurs. The heart rate module picks up the electromagnetic pulse, and in turn outputs its own pulse. The Arduino was programmed with the pulseIn() function to time how much time elapsed between each individual pulse (in microseconds) and converted those measurements into seconds, and finally into beats per minute.
This was what seemed to be a fairly basic sensor, since all it did was emit a pulse when it detected a heart beat (in theory), however just this module alone proved to be quite a challenge.
On the fabrication scale, it is a surface mount chip and thus is not designed to be soldered well with wires and a bread board. It requires a 32 Khz crystal, which also was a surface mount piece but in the end we ended up soldering the crystal to the chip with wires. Thus connections were often spastic and buggy when trying to test this module out, and it often took a considerable amount of time just to get it to work. The wiring itself was not so difficult compared to making sure all the connections were suitable. Also, the Polar Heart Rate Sensor must be continuously wet in order more readings to be picked up by the module, probably because it was designed for athletes who sweat a lot, thus providing a natural conductive medium.
Other constraining factors between the heart rate module and sensor is that the distance between the two must be kept to a minimum, roughly 80 cm according to the data sheet. Also the orientation between the sensor and the module can be at times difficult to maintain, and the signal between the two can be easily lost.
While taking measurements, sometimes the heart rate module was noisy. Data was collected for the difference between an actual beats per minute count measured via our own pulse, and the value that the module was reading. The histogram is plotted below, with the expected value plotted in green.
While there were a few measurements particularly off, on the average the discrepancy remained close to zero. In order to compensate for noisy readings in our code, we implemented an averaging function that puts less and less weight on older measurements and more and more weight on newer measurements.
Overall, this little chip gave many a challenge and the occasional headache, but provided an interesting learning experience with monitoring life signals. However, my personal recommendation is if anyone tries to replicate a similar project, or just isn't too experienced with working with components like these, buy the pre-made interface with a breakout board. The extra cost is well worth the ease of use and construction.
We're going to give an overview of how we fabricated the suit and cannon, and how all these distinct pieces were put together. The fabrication of the project consumed the majority of our time and effort. There is plenty of soldering (the opto-isolator boards), sewing (EL wiring), and connecting (connectors for everything - includes soldering and shrink wiring exposed leads).
We start with the suit and EL wire. We had to sew the EL wire into the suit to make it durable. This also included sewing the electric wiring into the inside of the suit. Each EL wire is driven by two leads. This means for each EL wire, there are two power wires. We were lucky and had a whole spool of twisted wire on hand to give us the lengths we needed as well as the quantity. So, each EL wire had two wires that were sewn into the suit and gathered together at a connector. We had 4 EL wires in the jacket for showing heart rate info, and 6 wires to show laser hits. 4 EL wires were likewise sewn into the pants for showing heart rate info. We used fishing line to sewn the EL wire and their corresponding wires into the clothing.
After all the wiring was sewn into place in the clothing, we created some connectors to easily interface the clothing with the Arduino boards. We used common D-Sub connectors for this purpose.
To interface with the EL wire, we fabricated some opto-isolator boards as discussed in the EL wire section. We placed one of these into the Control Box with an Arduino, an Inverter, and the heart rate sensor. This is the central processing unit of the project. The Arduino gathers heart rate data and ir receiver data. It then switches on and off EL wires according to heart rate data, and also transmits ir sensor data to a secondary Arduino. This Control Box was attached to the inside of the jacket using industrial velcro. Other methodologies certainly exist for the placement of this box. In fact, you could even develop a more decentralized system with parts scattered and sewn throughout the suit, instead of a central box.
The second endeavor was creating the arm cannon. We purchased two sizes of PVC pipe for this. We needed a 2" diameter pipe for the lens and ir emitter, as specified in the IR sensor section. The second pipe was chosen to act as the "cannon" and would house the secondary electronics of the overall system. An Arduino was placed inside the cannon to pulse the ir emitter correctly, as well as receive ir sensor data from the primary Arduino, and flash the appropriate EL wire. In the demo for class, we separated the EL wire flashing and ir emitter pulsing into 2 separate pieces because we hadn't constructed 2 full suits. However, the intention is that the cannon Arduino connects to the suit through a connector in the arm and controls the EL wire associated with laser hits. The firing mechanism was a simple push-button that dangled near the cannon holder. The cannon holder was just a wooden handled screwed into the PVC pipe.
The last piece to the puzzle was the Polar Heart Rate Monitor. It is a typical heart monitor used by athletes. As such, it is designed to wear around the upper chest. From this distance, the Heart Rate Sensor in the Control Box should wirelessly receive pulse info and react appropriately.
Another EL wire design attached