a. Common interfaces ( yellow blocks ) 1. ISP Programming port 2. ON/OFF Switch 3. UART Serial port 4. M-Blocks Bus which have the following standard.
------------------------------------------ Vin - Input Voltage from battery Vcc - Regulated 5V 3.3V - Regulated 3.3V SCL - I2C Clock Bus SDA - I2C Data Bus S3, S2, S1 - Slave select for SPI bus MOSI, MISO, SCK - for SPI bus only ( SPI bus is left for further use, I have not develop any sensors or devices through SPI communication ) TX - Transmitter for UART - connected to PC for debug only RX - Receiver for UART - connected to PC for debug only -------------------------------------------
b. Specific interfaces for Motor Module 1. SN754410 H-Bridge 2. External Power Input 3. Motor Connectors 1-4
2. Software side Except the Controller Module which is a master I2C device, all other modules are slave I2C devices. The design of the program is divided into three parts:
1) I2C communication among the modules, 2) UART serial communication for debug only , 3) The functional logic for controlling devices such as motors or servos.
I developed the program in WinAVR and built the hex file using avrdude. If you are interesting in the program, please download here. motor-module.zip
I use atmega8 to make all the communication and controlling. Atmega8 have three timers providing three PWM Channels. It is able to control the width of the PWM to the SN754410 H-Bridge IC by controlling the values of OCR1A ( motor 1 PWM) ,OCR1B (motor 2 PWM) and OCR2 (motor 3 PWM).
For the detailed information of Atmega8, please refer to the data sheet.
The protocol is very simple.
[ch][dir][low-power][h-power] , 1 byte each
[ch] set the motor channel , value = 0,1,2 [dir] set the forward direction or backward direction of the motor, value = 0,1 [low-power] and [high-power] set the speed of the motor, value = 0-255
Example: 00FF -> set ch 0 (left motor), dir 0 (forward), power = FF = 256.
The routetime set_power(uint8_t ch , uint8_t dir,uint8_t power) control the motor, direction and speed of the motor.
As I am not a master in programming micocontroller, many of the coding, especially the hardware configuration, or library are "borrowed" from other's projects.
So far, the Motor Module is working. It received commands from Controller Module and run set_power() routine to generate the PWM for the H-Bridge and control the speed of the Motors. My final version is to make the device which provide feedback parameters to the Controller Module. To make it as a close-loop control. I will borrow the design from the controller board of the openservo project. The controller board is a I2C slave device and it have feedback parameters to the controller board. All the parameters are saved in the registers ( flash memory ) of the micro-controller ( atmega8 or atmega168 ) and permanently in the EEROM as in the following diagram.
Reference websites: 1. Dr. Pascal Stang have contributed to the programming and design of the hardware. It is worthly to study his design if you want to learn avr-gcc programming and hardware design. I have implement the I2C master device from his design. http://hubbard.engr.scu.edu/embedded/
2. Openservo project, the opensource servo controller is based on atmega8 or atmega168 and avr-gcc. The design is very good. http://www.openservo.org
3. Paparazzi UAV project Paparazzi
is a free and open-source hardware and software project intended to
create an exceptionally powerful and versatile autopilot system by
allowing and encouraging input from the community. I implement the PPM decoding for my 6 channels Radio Transmitter by referring to the UAV project.
M-Blocks 2008-05-30 17:39
It is great if you find the information useful.
ayu 2008-05-30 10:27
Hi M大大，
Its so cool for your project.
iRobot 2008-05-29 11:51
I love to read it.
The information are very useful.