SOLAR CAIRN

For my final in Advanced Micro-controller workshop I was interested in creating a system that utilized all the elements I have learned throughout the semester and apply that knowledge into a working prototype. I am interested in the usability of RF Transceivers as a viable communication device specifically outdoors. I am WELL AWARE of the ease andspreading trend of the Zigbee platform, but I had these old TRW-24G's, which are using the Nordic Semiconductor nRF2401A Transceiver that I wanted to use. I am also interested in the sustainability of creating a device that is self perpetuating and self reliant. The final ingredient is that it may serve some purpose.

I envision this functioning in many of the same ways that rock cairns fuction, they are directional devices. However what if the beauty of these rock piles could be reattributed to an audio signal. This project is intended to help me find my way.

I found a solar panel array that provides enough power so that I can charge eight NiMH rechargeable batteries. By using a charging IC from Benchmark Technologies I made this possible.

The second phase was the RF Transceiver which transmits data between the nodes of the network.

The third chase is a ultrasonic transducer that senses movement within 3m.

The final phase is to incorporate all of these elements and a Microcontroller (18F2320). A task I would find to be far more difficult than one would expect, but this is an advanced class and I surely have a few hundred hours to sacrfice.

In phase three I determined that to run the Ultrasonic Transducers I needed a series of Op-Amp (TLC2272A)and a Darlington array(ULN2003), and this was just to test. I ordered the parts immediately, however they did not arrive in time for the final presentation, but perhaps for the show, three days later. I was able to find during this time both a working schematic diagram of the circuit as well as code that will run it. I chose the PIC chip as a launch pad because of it's wide array of onboard functionality. I also found both the Op-Amp and the Darlington array as samples from Texas Instruments.

While looking for DATA I did find this Application report using the MSP430. This was a start. This was a part I wasn't really into getting into so I tried to stay within the PICBasic environment, at the very least on a PIC. I then came across this code. Which was helpful, and was a good way to view what I needed to make happen, just not the right path. I think this was written in C and despite my efforts I haven't made the jump yet. Then through the PIC BasicPro user group I was able to find, not software for Ultrasonic tranducers but a slow pulse width modulation program or (SPWM) This seemed to be what I needed, I knew I was creating a square wave at 40Hz and this program allowed me to do that. However when I tried dumping it to the PIC I continually got error messages. At this final stage of this ordeal I began erasing code.This worked for a time, but eventually it broke before the out-of-memory error was called. A frustrating tangent that took a few days. What is best is that this all happened before I really had too much knowledge of what was going on in the curcuit.

Over the course of the past three weeks I found myself looking online whenever my plight seemed pointless. I came accross another nice example of code in C again. It would seem that the most common use for this transceiver is to send RS-232 data. I also found the site of Steve Cholewaik helpful as he has been working with these transceivers recently.

At this point I was forced to redesign the interface. I determined that perhaps switches are the best way to go. It became evident that I was using power nearly all the time. It also became evident that this system was not as resilient as I had hoped. Due to a lack of testing I am unable to determine how long the transceivers will function. I will be implementing a sleep command on the PIC to compensate for the time when the batteries are not being charged.

What is unfortunate in this prototype is that I was unable to optimize my power consumption as much as I would have liked. I remain positive that the system will work, just not how well. I also am having trouble with the fact that there is a really loud buzzer on each of the units. I would much prefer an actual audio track or even bird calls. In dicussing this project with friends and colleagues, the benefit this would serve for the hearing impaired is evident. I developed this project as a way-finding device. I can see how, even in an urban environment the benifits of audio directional navigation would be wonderful.

I chose the design of this for it's optimal size and convenient invisability. For the ITP Winter Show however I decided to use the Google Pin Icon as a stand. I found my materials and began construction.

 

For the show I wanted to give a not-so-subtle nod to the Google place markers.I made three of these "pins" as stands for my device protoype. The three were completed as the day turned into the day before. I used Maple 3/4" Plywood, cut it down and stained it Cherry. This was more in response to Google than the actual aesthetic of the piece. I have three. If you are interested in these stands please let me know.

 

This was the first time I had ever used a polyurethane stain and I found it streaked quite easily.

In the final hour after testing a set of ultrasonic sensors wired with a darlington array, and two op-amps I decided to switch to the Maxbotix Ultrasonic rangeFinder:

The functionality of the prototype could have had problems with my wiring of the sensor, once I tested with the Maxbotix the unit worked well.

I admit to being defeated by the sensors I first purchased and hope that I can use them in the future. It is also important to add that the Maxbotix device was rough eight times the price.

But it worked, so. . . .