Hardware Hacking Projects for Geeks

252

Part II: Advanced Hacks, Tools, and Techniques

Software Setup Instructions

After you have verified that power is going to the chips, it is time to pro-

gram the microcontroller inside the IR cannon and the hit-sensor board. I

chose the PIC16F876A controller, which is versatile and reasonably priced.

You will need to locate a programmer for this part; I used the ICD2 pro-

grammer/emulator from Microchip. A large number of companies offer

low-cost (less than $50) programmers on the Web. Do a quick search for

“PIC programmer” and ensure that the model you choose can program the

PIC16F876A (or whatever controller you use).

I wrote the control software for this hack in C to allow easy debugging. I

used the C2C compiler from http://www.picant.com/ as my C compiler. The

very efficient C2C compiler targets the PIC family of processors.

After you purchase a programmer,

download an evaluation copy of the

C compiler. Compile the code, and

then program the processor.

Software operation

The software looks for incoming IR

signals and generates outbound IR

cannon signals. A simple flowchart

illustrating the logic is shown in

Figure 13-13.

The IR cannon can be fired only

15 times, and the vehicle can take

only four hits before it becomes dis-

abled. Note that the four LEDs are

used for three different purposes;

the total number of hits will display

on the LEDs in binary notation.

When a near miss occurs, the LEDs

will momentarily flash. After each

shot, the total remaining shots flash

in binary on the LEDs. When all

hits are exhausted, all of the LEDs

flash on and off. I’ve provided all

the source code for the project in

Exhibit B so you can make your own

modifications.

Figure 13-13: System software flowchart

Initialize system. Set

HIT_COUNT=0,

SHOT_COUNT=15

Has the IR sensor

been triggered?

YES

NO

Is the IR

sensor signal duration

at least 200 msec

long?

NO

YES

Pulse all LEDs ON

for 200 msec

Near miss

Has a

FIRE_LED signal from

the radio been

received?

YES

NO

SHOT_COUNT=

SHOT_COUNT-1

Light up in binary a

number of LEDs equal to

SHOT_COUNT for 1 sec

Is SHOT_COUNT=0?

NO

YES

Generate a 38kHz signal

modulated at 2(or 3) kHz

for 500 msec

HIT_COUNT=HIT_COUNT

+1

Is HIT_COUNT > 4?

NO

Light up a number of LEDs

equal to HIT_COUNT

YES

Flash all LEDs

on and off at a

rate of 1Hz

Destroyed

Fire IR cannon

Software Setup Instructions

ch13_rc.indd 252

1/22/2002 4:44:29 PM

253

Chapter 13, How to Make RC Cars Play Laser Tag

Compile the code

Download a copy of the C compiler and install it on your PC. You will be

able to run the demo version for a few weeks before you need to enter a

validation key, which you can purchase if you like the product.

Start by creating a New Project, named whatever you like. You can see the

New Project menu item in the upper left of Figure 13-14.

Next, create a new file and either type in or download (from http://www.

oreilly.com) the C code into the compiler editor. The New File menu item is

shown in the upper right.

Save the file using a name with the extension “.c”. Add the file to the proj-

ect, as shown in the lower left.

Figure 13-14: Software compiler operation

Software Setup Instructions

ch13_rc.indd 253

1/22/2002 4:44:29 PM