Sensor Report [Final]

Sensor Report




Steve Spalding
IMDL

Tracker





































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 for collision detection.

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

Sensor Name: RF-KLPA 4800bps



Figure 2.a Transmitter Figure 2.b Receiver



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 receiver units mounted on Tracker. Tracker will use this information to determine the location of the external beacon.

Theory

In theory, the two receiver units, located on either side of tracker should receive 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 receiver 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 receives 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 receiver pairs. Further testing has proved that there are a great deal of external variables that makes this simple resolution of voltages nearly impossible to apply in practice.

Scope

Two receivers and a single transmitter will be used. The receivers 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 solar cells



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 pull-up resistor they are
capable of producing logic high or low depending on which cell is receiving 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.

Data

Experimental Voltages:

.01V with no significant ambient light
.25V with moderate light (well lit room)
.40V direct exposure to a flashlight
.77V theoretical maximum voltage when exposed to direct sunlight.

Under normal experimental conditions these solar cells operated between .25V and .30V.

Experimental Current

Using a 1000Ohm DIP package resistor

Negligible (outside of the voltmeter’s resolution) drive current for the solar cells.

As a note to those who may want to use photovoltaic cells like these for powering circuitry or significant light tracking on solar power alone. In order to use these successfully in those applications one must use several (theoretically six, but very likely many more than that) in series. These will only produce at maximum of .77 volts and a very low current. Also, one would do well to use a voltage trigger like the 1381E (rated for 2.2V) and a Miller Engine in order to store power. That way your circuitry can remain idle until enough power is collected through the Miller Engine and then your robot will turn on in “bursts”. Selecting the appropriate trigger voltages and using a significant amount of solar cells will reduce the idle time between these bursts.