The handyboard is the heart of the rover, which contains important circuitry, the microcontroller, memory and allied devices. The handyboard is nothing but a PCB which is used in several amateur robotics projects.

Several different circuit boards were considered for use on the rover. Among them were the miniboard and the 6.270 board. However we narrowed down our choice to the handyboard because it is more advanced than a mini-board and is more simplified as compared to a 6.270 board.

Of all the microcontrollers researched upon, our microcontroller choice came down to two, the Motorola m68HC11 or the Intel 8051. When researching these microcontrollers, we discovered that 68HC11 had the following useful features.

1. Easy Serial Programming
1. Easily Upgradable Memory (with memory management)
2. Low Power Consumption
3. High Performance Timer
4. Analog/Digital Conversion System
5. Pulse Width Modulator (useful in motor driving)
6. Low power consumption and high performance operation at bus frequencies upto 4 MHz.
7. A fully featured interrupt system with EEPROM on most derivatives.
8. Includes a math coprocessor performing fast 16 bit integer multiplication and division increasing throughput.
9. Powerful bit manipulation instructions with 6 powerful addressing modes and power saving STOP and WAIT modes.
10. Many devices offer upto 6 additional memory expansions to access more than 1 MB.
11. A four channel DMA unit on some devices performs fast data transfer between two blocks of memory.
12. All chips support serial communication provided by on-chip interfaces.
13. The AD system is software programmable to provide single or continuous conversion modes including selection of Pulse Width Modulation (PWM) options to support a variety of applications.

The interfacing circuits that were chosen were present on a board known as the F1 Controller (also known as the Handy Board), an embedded controller based on the MC68HC11F1 microprocessor. It has been designed so that it can be configured for many diverse applications with the minimum of effort. It can be plugged directly into the serial port of a PC and allow us to talk to it and manipulate the I/O without having to write any programs, to test it.

The Motorola HCMOS MC68HC11A1F4 is thus an advanced microcomputer containing highly sophisticated on-chip peripheral functions. An improved instruction set provides additional capability. The fully static design allows operation at frequencies down to DC, further reducing its already low power consumption.

Features available for the microcontroller are:

1) 512 bytes of EEPROM

2) 256 bytes of RAM

3) Enhanced 16 - bit timer system

4) A new serial peripheral interface

5) 8 channel 8-bit A/D converter

6) A real time interrupt circuit.

It is a 52 pin IC. It has a DMA controller, internal clock generator, 2 interrupt request pins, 5 I/O ports viz. A,B,C,D,E. The I/P signal voltage given to the controller is 5Volts.

The MC68HC11A1FN uses 2 dedicated pins ( MODA & MODB) to select one of the two basic operating modes or one of the two special operating modes. The basic operating modes are Single-chip and Expanded multiplexed, and the special operating modes are Bootstrap and Special Test. Their selection is shown below:

We will be using the bootstrap mode only. In the bootstrap mode the bootloader, which is a program present in the EEPROM that contains all the vector addresses; reads a 256 byte program into the on-chip RAM. After this is done the control is automatically passed onto the program at memory address 0000.

The O/P of the IR sensors and the shaft encoders are given to Port B and Pulse counter of the 6811 respectively. Now the 68HC11A1FN is programmed in such a way that it keeps checking the inputs at these two ports. The input from the shaft encoder is continuously added. Hence if the rover has to back a certain distance then the number of revolutions made by the wheel that has been counted using the shaft encoder can be found out by the timer count and thus the rover can move back by the same number of revolutions.

Also if the sensors sense an obstacle then the output of the sensors will go low. Immediately the port to which the sensors are connected goes low and hence during status check the controller knows that there is an obstacle and it stops the rover by interrupting the motors connected to the wheel. These are the two main functions performed by the controller

 The Handy Board Circuit Diagram

The heart of the "rover" is the Motorola’s MC68HC11A1FN 8bit microcomputer. It is a single chip micro computer which contains highly sophisticated on-chip peripheral functions of 4K bytes of ROM ,512 bytes of EEPROM, 256 bytes of RAM, enhanced 16-bit timer system,8-BIT pulse accumulator circuit ,an enhanced non-return-to zero. Serial communications interface (SCI),a serial peripheral interface,8 channel 8_BIT A/D convertor etc: which help to drive the rover. The overall CPU and memory circuit consists of the controller, the RAM, the DS-1233 reset regulator, the quad Schmitt NAND gates, the 3 to 8 decoder, the LCD and the connectors for the various outputs viz: for the serial interface, LCD display, control outputs, multiplexed address data bus, the analog inputs, the buffer etc. The clock for the controller is provided by the oscillator ckt formed by C1, C2 and the 8-MHz crystal. The controller is used in the expanded multiplexed mode. The controller is made to work in bootstrapped mode to download the software into the RAM through serial communications interface. The port A has the lower 8-bits of address and the upper 8-bits are taken from port C which have multiplexed address data bus and are connected to the RAM through a buffer which latch the address or data depending upon "the address strobe " (AS) signal given by the controller. DS 1233 is a special reset power regulator chip which makes the controller OFF if it’s voltage level goes below the 4.5 V DC level.

The 74HC138 is a 3 to 8 decoder which generally maps devices onto an address space. The enable inputs of decoder are important because they should not become active at the same time as RAM chip or else it would lead to "bus contention". Depending upon A13,A12 and the R/W signal, the O/P is selected which gives the O/P fromY0 to Y7.When the R/W signal is high,Y7 will be selected and the digital I/p’s from 74MC244 are activated. Similarly, for write operation Y6 the motor O/P’s would be selected. Controller gives the additional functions for various signals like for the IR receiver, the LCD control, the IR transmitter, piezo O/P etc:. Out of the 8 digital I/P’s two are for shaft encoder and four are for the sensors.

J11 is the coaxial power jack to which 12-15 Volts DC is given. It gives rectified output through LM2931Z-5.0 regulator which gives a 5Volt output. RJ 12 is the jack for supplying power to the handyboard as well as giving the signals. The battery charging can be done with the SW4 open and the fast charging is done with the help of "ZAP mode".

The board communicates with the RS 232 system, but requires external circuitry to convert its own signals which obey digital logic norms to RS232 signals and this function is made possible by interfacing the MAX232 IC with the host computer. A DB 25 pin female connector makes the interface between the host computer and the serial interface board.