robot line folower

Introduction

One of my student has made a disgraceful robot that used two stepper motors and with a simple IR sensor. Yes, above picture is what I'm talking. Without battery carrying, a little bit torque of the stepper and misalignment of driving shaft, makes it crawling not walking, but first demo, showed quite impressive to me. He said he wrote a couple of program lines using C, his robot can track the black tape. I feel delighted his intention and endeavor. I thought, " he borrowed me DS5000, expensive one, a soft uController with internal bootloader, why shouldn't try with our learning board C-52 Evaluation Board instead". Another one, told me the same day "I found the L293 Push/Pull Four Channel Driver at Ban-Moah, it costs 1.5 US$ ". I've been searching this chip for a year. The MiniBoard, a Motorola 68HC11 Robot Controller board designed by Fred G. Martin, also uses this driver. The day after, I then decided to prepare the page describing how to use C-52 EVB as a robot controller board. I asked my student for competition, build yourselves robot that can track the black tape. Prize for the winner is 100 US$, with a bit condition that the winner must pay for a big party at Soi Jinda's Somtum (Papaya Salad) shop. And one of the competitor is me. I thought the rule should be conceived roughly by students and technically by me. The picture on that day will put here soon.

C-52 EVB resources

Beforehand, let look at available resources of C-52 EVB for robot experiments.

Actuators	DC motor	PWM with timer2 helps	P1.4,P1.5, P1.6,P1.7
Sensors	digital/analog	IR detector with comparator chip/ for analog input, see use of PIC16C711	digital input/T0,T1 for pulse input
Brain	C program	available code and data space approx. 32kB	8000H-FFFFH
Program Downloader Running without monitor	PAULMON2 with PAUL's startup header	9600, 8n1	P3.0 (RxD) and P3.1 (TxD)

DC Motor Driver

Basic circuit of using L293 forms an H-Bridge Driver is shown in Figure 1. As shown for such inductive load as DC motor, external diodes for suppressing back EMF must be connected. The MiniBoard uses L293D instead, the L293D has internal diodes, however providing a bit less driving capacity, i.e., 600mA @4.5V-36V. From the truth table, we see that direction of the motor can control by pin C and D. VINH enable/disable power to the motor, thus for speed regulation, we then use this pin for PWM signaling. See details, L293.pdf data sheet.

Figure 1: Basic circuit of L293 forms H-Bridge Driver

A circuit connecting C-52 P1 to L293 driver chip is shown in Figure 2. As shown Enable pin 1 connected to P1.0 is for PWM signaling. We use additional inverter at pin7 and pin 15 to provide proper logic for easy directional control. Please note that pin 4,5,12,13 are tied to ground and if heat sinking needed, one method is to make a large area of PCB or soldering it with a metal sheet, say.

Figure 2: Connecting C-52 EVB P1.4-P1.7 to L293. External diodes must be connected for L293(not shown in circuit diagram). My latest design put additional inverter for PWM signal at pin 1 and pin 9 to prevent full power delivering to DC motors when resetting the 89C52(i.e., all bits of P1 is logic high). Check the logic of PWM pins for another microcontrollers.

Line Tracking Sensor (I have to KUK)

Since there's no ADC for 89C52 chip, each competitor may build their own Line Tracking Sensor, some may use LM339 QUAD comparator with IR transmitter and receiver, some may use LDR as described in Line Follower Robot . With an external comparator, it may not necessary to have ADC, but with LDR, we need external ADC. " Having additional ADC for 89C52 would be better", I thought. How can we provide ADC for 89C52 with a cheap method? I chose PIC16C711 with 4-channel ADC, and 7-pin input port. Interfacing to 89C52 is done with simple PISO protocol by using RB0 for SCLK and RA4 for SDA. The code for such purpose was written in C, here is the source file, C52ADC.C and the HEX code, C52ADC.HEX. After some initialization, the 711 chip wait for trigger read signal at pin RB0, i.e., high-to-low transition, then it responses by sending 40-bit through RA4(SDA) with low-to-high transition. 40-bit data stream begins with LSB of ADC0 to MSB of PORT B. Example of program fro testing ADC is ADC.C and the hex file is ADC.HEX.

Figure 3: Using PIC16C711 to be a 4-channel ADC and 7-bit input port for C-52 EVB.

Simple Power Supply and Charger Circuits

Figure 4 shows a simple power supply circuit. I have tested with KABO, it works fine. For those who have a big capacity rechargeable battery, the resistance value of R can be selected for approx. 10% output charging current. DC in can be higher if your battery voltage higher than 8.4V, say. To ensure the output current is within the value calculated by R, measure DC current before. The maximum supply for LM317 is ~35V.

Figure 4: Circuit Diagram of battery supply +12V Alkaline and +8.4V NiMH with a constant current recharger circuit. For ~20mA, use R~60 Ohms. S1 is main switch for CPU and L293 circuits.

Using PAUL's Startup Header file with Micro-C

Before writing PWM generation for testing above circuit, let study how to use Paul's header. With a PAUL's startup header at the beginning of the application C program, after successfully downloading the hex code, just press RESET, the 89C52 then will run the application instead of PAULMON2 monitor program. As long as the program remain in SRAM, running the program can only be done with pressing RESET. To return to PAULMON2 prompt, turn the board power off for a while, then back the power on again. This concept of startup header allows us to use C-52 EVB as a dedicated controller beside as a learning board. Originally Paul has made with entirely in Assembly code. However, I have adapted for Micro-C Compiler. I have put the header for startup code in the startup and runtime library for small memory model. The file C52ROBOT.ASM, will compile and link to the main( ) function with S=c52robot.asm when invoking command coordinator. Example of command line is;

c:\mc\cc51 %1 -ilp h=c:\mc m=s s=c52robot.asm

%1 is hello(.c), say

Let try hello.c and compile with above command line, download the hello.hex into the C-52 board, then press RESET, see what happen?

Manual Control Program demonstrates PWM generation with KABO

One method of delivering DC power to motors is to use PWM. The PWM method supplys DC pulse with fixed frequency but with adjustable duty cycle. I used TIMER2 in AUTO reload producing 1000Hz PWM frequency. Each time executing has entering into service routine, a 16-bit PWM1 was shifted out to P1.7 and PWM2 to P1.6. Main program has a task that set the power for motor1 and motor2 by writing 16-bit PWM pattern into PWM1 and PWM2 for motor1 and mortor2 respectively. The service routine for timer2 is put in startup code. See example program, KABO1.C and C52ROBOT.ASM, for PWM demonstration with manual control. I have designed and built my own robot for the competition also. It names KABO having differential drive method. As shown in right-hand side, is the rare part powered by C52-EVB. The motor driver chip L293D and a 74LS04 are put at the soldering pad.

Ving-Peaw Competition

I suppose there should have ten robots to be competed. Details Rule and Scoring will be launched soon, day by day changed. But first of all, competitors must know how difficult of the circuit and programming are. Hear is the actual course layout.

Figure 4: Actual Course Layout for Ving-Peaw Robot Competition

The original idea of what kind of the competition would be, came from Zongwit. Each round has two robots. Each robot must run along black tape and try to touch the the other's target. Who touch first will be the winner. The slower is allowed to detect the faster, shifted out of the line for 20 seconds, then back again. No limit for the robot size and uControllers, you may use ranging from a PIC16F84, 16F873/877, 89C2051/4051, 89C51/52/55, or 68HC11, say.

C-52 EVB Robot Controller Links