Weekly Report 7.18.06

This week I adjusted my motor control code in order to try to keep the robot from getting stuck in corners quite as often. I also created a test circuit for my RF and discovered that there is a change in the recieved voltage at the linear test line that is related to the distance that the device is away from the transmitter. The only issue is that there is a large amount of variation in how much voltage is recieved at any given point. After filtering it through a comparator, however, this system should be able to differentiate signal strength, on average.

I also fixed a problem that I was having with my power system. As I have added more systems, the current draw has increased. It was starting to cause serious problems with microprocessor resets. I installed new batteries that are capable of pushing a larger amount of current and this seems to have helped.

Finally, I found an LCD design that can fit (at least temporarily) on my robot for when I need to debug it and I wrote the code to get it to work.

Before the end of the week I hope to fully integrate RF and begin field testing some code involving it.

Sensor Report 7.3.06

1 - Infrared

Sensor Name: GP2Y0D340K IR Sensor - 16" Trigger


Figure 1.a


Figure 1.b - Wiring Diagram


Vendor

Hobby Engineering
180 El Camino Real
Millbrae, CA 94030
1-866-ROBOT-50 (toll-free 866-762-6850)

Objective(s)

Two IR sensors were purchased to serve as Tracker's 'eyes'. Functionally, they ensure that Tracker stays at least 16" away from any of the objects that they detect.

Theory

These IR sensors are used in the typical fashion. When the robot gets within 16" of a target the output line goes high. The robot uses this information to send a signal to the motor that then turns in order to avoid collision with the object.

Scope

Two IR triggers are mounted on either side of the robot robot for collision detection.

2 - Radio Frequency Transmitter/Reciever (Special Sensor 1)

Sensor Name: RF-KLPA 4800bps



Figure 2.a Transmitter Figure 2.b Reciever



Figure 2.c - Wiring Diagram


Vendor

1-303-284-0979
Spark Fun Electronics
2500 Central Ave.
Suite Q
Boulder, CO 80301

Objective(s)

The main 'special' sensor on tracker. The transmitter will be deployed on an external 'beacon' unit. It will transmit a signal to the two reciever units mounted on tracker. Tracker will use this information to determine the location of the external beacon.

Theory

In theory, the two reciever units, located on either side of tracker should recieve slightly different amounts of power since they are not directly facing the signal source. As of the writing of this report, I plan to exploit this presumably small difference in power by 'tapping' the antennae line (pin 8 on the reciever diagram) and running the resulting voltage through an LM339N comparator. This device (described in the section on photovoltaic cells), has already proven capable of resolving voltage differences as low as a hundredth of a volt. It seems likely that as long as the antenna recieves an analog voltage that is linearly related to the distance from the source that this technique can be used to find the direction (left or right) between the transmitter and reciever pairs.

Scope

Two recievers and a single transmitter will be used. The recievers should be capable of resolving whether the robot should move either left or right.

3 - Photovoltaic Cells (Special Sensor 2)

Sensor Name: BPW-34 clear-epoxy solarcells



Figure 2.a


Figure 2.b - Block Diagram LM339N


Figure 2.c - Circuit Diagram LM339N

Dimensions: 1/8"

Vendor

1-866-ROBOT-50 (toll-free 866-762-6850)
Hobby Engineering
180 El Camino Real
Millbrae, CA 94030

Objective(s)

These photovoltaic cells (2) small (1/8") solar cells. They produce a voltage that has been measured between .25 and .38V (theoretically, in direct sunlight, they should be capable of producing up to .77V). They are being used as an optical switch.

Theory

In their normal state, the solar cells are only capable of producing a voltage. However, using an LM339N Comparator, running the positive terminals of each solar cell to the V+ and V- inputs and using an external pullup resistor they are
capable of producing logic high or low depending on which cell is recieving the most light. Another advantage of this circuit is that since the cells produce power on their own, they do not draw on any external power source. While this is a small difference, in the scope of things, it is a positive side-effect.

I also theorize that the photovoltaic cells have a faster 'reaction' time compared to the historically 'slow' CDS cells, making them a handy replacement for the usual work-horse of light tracking.

Scope

Two photovoltaic cells are being used to resolve the directions left and right.

Weekly Report 07.04.06

Over the break week I did several things. First, I mounted my IR sensors and got rudimentary obstacle avoidance working. The code will be re-written to take advantage of additional sensors as they become available. I also had to order a few more parts in order to solve a space limitation I was facing (I needed to order an LCD with a smaller pin requirement and another perf board for mounting).

In addition to obstacle avoidance I built and tested a circuit for light following involving a Comparator and photovoltaic cells. I believe this circuit will be more efficient than the usual CDS cells. Also, the 'sensors' do not require additional power as they produce their own. While the cells are far to small to produce sufficient power to be worth routing through the engines, at the very least they do not consume any energy.

By the end of the week I should have these sensors mounted on the robot and the additional software to run them should be created. At that point, the only major system that is needed will be the RF tracking ability.