Programming and Controls Workshop – The Basics

Tom Barch

Agenda System Overview

How the systems works – Controls Block Diagram Robot Controller Operator Interface

Controls Overview of the controls used and how they work

Programming Default Code Reference Guide – How an why to use MPLAB and IFI Loader – How to install and use Default Code – An overview Downloading the Code to the Robot Controller

Pneumatic Controls Overview of the pneumatics system – Block Diagram Controlling the pneumatics – Understanding the controls

Hands On Demonstration How to download and test using a real system

Robot Controller or RC

Operator Interface or OI

Tether Communications

Radio vs. Tether communication

If the controllers ‘see’ a tether cable connection, then they will communicate via the tether port.

If no tether connection exists, then they will attempt to use the radio signal.

Note: Connecting via radio at the competition other than during a match is not allowed and can be dangerous if another teams operator interface controls your robot.

Controls Understanding the controls will help to understand the

software variables and how the software is modifying and outputting them to get the Robot to move.

The joystick is read by the Operator Interface and is transmitted to the Robot Controller. It usually drives a pwm output which controls a Victor 883 or 884 speed controller. The speed controller maybe wired to a drill motor.

By pressing the joystick, we hope to control the speed and direction of the motor to get the Robot to move.

Lets start with the Joystick.

Joystick The joystick consists of two potentiometers mounted to a

stick that vary as the stick is moved along its axis. One potentiometer is mounted in the x axis or left – right

direction and the other is mounted in the y axis or forward – backward direction.

As the potentiometer moves from one extreme to the other, the operator interface reads the voltage from 0 to 5 volts.

This voltage is broken into an 8 byte variable that ranges from 0 (0 volts) to 254 (5 volts).

The variables in the software for the input ports on the OI are pX_axis where x is port 1 to 4 and the axis is x, y, or wheel. (example p1_y is port one, y axis or forward/backward)

Joystick - continued

Full forward in the y axis will result in p1_y = 254.

When the joystick is in the center, p1_y = 127.

Full backward p1_y = 0.

Victor Speed Controller The input to the speed controller is a pulse width

modulated (pwm) signal that varies from a value of 0 to 254.

In the software, these variables are labeled pwm01 – pwm16 corresponding to the pwm input on the RC.

Battery and ground is supplied to two input terminals and the two output terminals can be wired to an electrical load like a drill motor.

At an input of 127, the two outputs which we will call m+ and m- are at 0 volt difference

As the pwm increases from 127 toward 254, the voltage varies from a positive difference of 0 to 12 volts.

As the pwm decreases from 127 towards 0, the voltage varies from a negative difference of 0 to 12 volts.

Victor 883 or 884 speed controller

Joystick to Motor The joystick variable is the same as the variable

outputted to the pwm output to drive the motors forward and reverse.

In the default software, port one y axis is output directly to pwm01 port:

pwm01 = p1_y; In the default software, port two y axis is output

directly to pwm02 port:pwm02 = p2_y;

The two of these make up the tank drive (two joystick).

The software also outputs joystick one x and y axis to pwm ports 13 and 15 to get one joystick drive.

Joystick Switches Located on the joysticks are four switches that are read

by the computer as 0 or a 1. When the switch is closed, then the variable is read as a one.

These switch inputs for each one of the four input ports on the OI are:

p1_sw_trigp1_sw_topp1_sw_aux1p1_sw_aux2

Spike Controller The spike controller is a relay or electronic switch that will

drive two outputs based on the inputs. The reason for two input and two outputs are to enable the

output to be driven positively or negatively to drive a small motor forward or reverse.

When the inputs to the relay are driven both as 0, then the outputs are both at 0 volts. One input is called Fwd and one is called Rev. One output is m+ the other is m-.

If the Fwd input is a 1 and the Rev input is a zero, then the m+ output will be 12volts and the m- output will be 0 volts.

The spike can be used to drive small motors, lights, air compressor, or any other 12 volt electrical load. The concern is the current draw which is much lower then the speed controllers.

Spike Blue Controller

Spike Truth Table The truth table for the input to output is as

follows:

Spike alternative circuit The spike can also be used to drive two

different outputs in a on/off sequence. An example would be two solenoid valves.

Programming the Robot Controller

Robot Controller Code MPLAB IDE v7.20 is the C programming editor

and complier from Microchips used to edit and compile the code.

IFI Loader is a program that will download the complied code into the robot.

None of this is necessary if the default code is used.

If modifications are necessary (custom functions are needed/variables need to change slightly), the code will only need modifications instead of a complete re-write.

Default Code Reference Guide Available from Innovation First website

http://www.ifirobotics.com/(in the Robot Controller section at the bottom)

Shows OI wiring/variables to RC variables/output for the default code functions.

Contains the variable listing for modification of default code.

FRC 2004 Default Code Reference Guide.pdf

Table of Contents

Joystick Function

Joystick plugged into port 1

Y-Axis is forward – backwards (tank drive)

P1_y is the variable used in the software to read this function

RC PWM1 is the port that the left side victor should be plugged into to make port 1 the left joystick for tank style drive

Single Joystick Drive Missing from default guide – It is on the

front cover but hard to read.

Connect the right drive motors to PWM13 and/or PWM14 on the RC.

Connect the left drive motors to PWM15 and/or PWM16 on the RC.

MPLAB Install Adobe PDF

document exists on CD

Has the defaults and instructions for installing MPLAB as well as the IFI loader.

C-BOT_Install_1-29-2004.pdf

MPLAB and Default code After downloading the default code, place

the unzipped files in a directory, preferable in c:\code\frccode.

MPLAB and First recommends a simple directory. My Documents is a complex directory in Windows 2000 and Windows XP.

Saving an old revision and creating a new one is done by copying the folder and pasting to new director (i.e. copy c:\code\frccode into a new directory c:\code\frccode1 and so on).

Opening the default workspace Do not use the file open command. Use the

open workspace command.

User_routine.c Most of the code changes will be made in

the user_routine.c file Custom code should be placed in

Process_Data_From_Master_uP function at /* Add your own code here */.

The specific functions for most of the inputs/outputs are in the Default_Routine which is at the bottom of User_routine.c The variables can be modified in the default

routine, but make sure to use new revision (directory) here so that changes can be reversed.

C Programming C is a popular powerful language that

requires conciseness with a wealth of operators.

Teaching C in a one hour workshop would be impossible.

The next few slides are intended to help understand some of the C language basics in order to make minor modifications to the default program.

C Language Basics C is a compiled language. The C compiler is a program that reads source code, which

is the C code written by a programmer, and produces an executable or binary file that in a format that can be read and executed (run) by a computer. The source file’s are a plain text file containing the text version

of the code written in correct syntax for the C complier. The executable file consists of machine code, 1's and 0's that

are not meant to be understood or read by people, but only by computers. This is the file that gets downloaded into the RC.

The compiler will make the executable file from the source code and check for syntax errors. The complier does not check for logic errors.

The best way to learn anything is to jump right in, so let's start by looking a simple C program.

C Program Structure

Code Comments Comments in C are done in one of two ways:

/* Comments are placed between text markers and can span multiple lines of text*/

// Comments on one line only

Most C programmers use the comment markers /* text */

Text should be green if the right markers are used in MPLAB.

Relational Operators You may have noticed the == sign used in the if statement.

Unlike most other programming languages, the = is an assignment operator. The double == is the equality operator.

== equal operator5 == 4 FALSE or 5 == 5 TRUE

!= not equal 5 != 4 True or 5 != 5 FALSE

> greater than 5 > 4 TRUE or 5 > 5 FALSE

>= greater than or equal 5 >= 4 TRUE or 5 >= 5 TRUE

< less than 5 < 4 FALSE or 5 < 5 FALSE

<= less than or equal5 <= 4 FALSE or 5 <= 5 TRUE

End of line markers Some of the code is ended with the

semicolon ;pwm01 = p1_y;

Braces mark the beginning as well as the end of the body of a function.

If (p1_y == 127){

p1_x = 127;}

Variables in C Valid names can consist of letters, numbers

and the underscore, but may not start with a number. A variable name may not be a C keyword such as if, for, else, or while. Variable names are case sensitive. So, Age, AGE, aGE and AgE could be names for different variables, although this is not recommended since it would probably cause confusion and errors in your programs.

Declaring Variables Variables are usually declared at the top of

the module or in a separate “header” file which usually ends with .h file type.

In the space before the variable or function being declared, is the data type the variable or function will return.

A variable can be assigned a value in the declaration statement.

C provides built in data types for character, float and integer data. A mechanism, using the keyword typedef, exists for creating user-defined types.

Data type - Integer Integer variables are used to store whole numbers. There are several keywords used to declare integer

variables, including int, short, long, unsigned short, unsigned long. The difference deals with the number of bytes used to store the variable in memory, long vs. short, or whether negative and positive numbers may be stored, signed vs. unsigned. Examples:

int count;

int number_of_students = 30;

Data types – floating decimal point Float variables are used to store floating point

numbers. Floating point numbers may contain both a whole and

fractional part, for example, 52.7 or 3.33333333. There are several keywords used to declare floating

point numbers in C including float, double and long double. The difference here is the number of bytes used to store the variable in memory. Double allows larger values than float. Long double allows even larger values. Examples:

float pwm23_new = 0.0;double pwm23_new2 = 1234567.89;

Data types - Character Character variables are used to store

character values. Character type is actually an integer value

that stores the ASCII integer value Char is often used as a 8 bit integer value.

Examples:char firstInitial = 'J'; /* stored as 74 */

char secondInitial = 'K';

Constants The preprocessor is a program that modifies your source file prior to

compilation.

Common preprocessor directives are #include, which is used to include additional code into your source file

#include <stdio.h> /* include standard commands*/

#define, which is used to define a constant.

#define pi 3.1415#define id_no 12345

Wherever the constant appears in your source file, the preprocessor replaces it by its value. So, for instance, every "pi" in your source code will be replace by 3.1415. The compiler will only see the value 3.1415 in your code, not "pi". Every "pi" is just replaced by its value.

Conditional Statements The if statement is used to conditionally execute a block of

code based on whether a test condition is true. If the condition is true the block of code is executed, otherwise it is skipped.

int main(){ int number = 5;

if (number == 5) { number = 2; }

}

Final C comments C has many more syntax and command

structure which would require a lot more training.

One other command that might be of interest is the ++ operator. In basic the command x=x+1 can be shortened

to x++. While this is confusing to most beginners, it allows shorting of the code.

The x++ command might even be used while evaluating a command.

int x = 2;if x++==2 printf(“x=/n”, int x);

Compiling the code In MPLAB, select the Project menu and

select the Build All command. The Output window will have the comments

on if the build was successful or if there are errors.

If there are errors, locate the error and fix. Be careful with where the error occurs. The

actual error can be many lines of code before the syntax error. An example would be a begin comment marker without an end marker. All the code will be commented out until the next end marker.

Loading the code into the RC IFI Loader is the program used to download the compiled code. Make sure that the RC program port is plugged into a serial

com port on the computer. Set the IFI loader to the com port plugged into. Press the program button on the RC and then press the

download button. The terminal window can be used in conjunction with the printf

command to display variables on the terminal window. Remember that the printf statement will output every time the

command executes. If the printf is in the slow loop it will print every 26.2ms or even faster in the fast loop. This may be hard to read with the data scrolling off the screen.

The buffer is a circular buffer so it won’t fill up. The old data won’t be there either, so you may need some type of logic to keep the data on the screen.

Pneumatic Controls Block Diagram

Pneumatic Controls The air compressor is wired through a relay controlled by the

pressure switch. When the pressure switch drops below the set switch point, the

relay is energized turning on the air compressor. When the pressure exceeds the set switch point, the relay is de-

energized turning off the air compressor.

Controlling the pneumatic cylinders is then accomplished through a single or double solenoid valve. “Single-acting” or single solenoid valve will extend the air cylinder

while the solenoid is energized. When the solenoid is de-energized, the air cylinder will close.

“Double-acting” or double solenoid valve will extend or open a air cylinder when one of the solenoids is activated and will close when the other solenoid is activated. After either solenoid is deactivated, the air cylinder will remain open or closed.

These solenoid valves are controlled via a spike.

Spike Truth TableSingle Solenoid Valve (two valves wired to M+ & M-)

INPUTS OUTPUTS    

Fwd Rev M+ M- Indicator Solenoid Function

0 0 GND GND Orange Off / Brake Condition (Default)

1 0 +12V GND Green Solenoid1 Activates (M+)

0 1 GND +12V Red Solenoid2 Activates (M-)

1 1 +12V +12V Off Solenoid 1 & 2 Activates

Double Solenoid Valve (both positives wired to M+ & M- with grounds to ground block)

INPUTS OUTPUTS    

Fwd Rev M+ M- Indicator Solenoid Function

0 0 GND GND Orange Off / Brake Condition (Default)

1 0 +12V GND Green Solenoid Activates Direction A

0 1 GND +12V Red Solenoid Activates Direction B

1 1 +12V +12V Off Solenoid Activation is unknown

Summary

There are other websites for resources.

The www.usfirst.org has many presentations on the subjects presented here.

Hopefully this has been informative and will help in the coming weeks.