Wireless communication for social robotics. Gu C. Department of Electrical & Computer Enginnering. National University of.

Transcription

1 Wireless communication for social robotics Gu C. Department of Electrical & Computer Enginnering. National University of Singapore ABSTRACT Wireless communication has been widely used in Social Robotics communication. In this project, I m focused on developing two Radio Frequency Wireless solutions. One uses Cypress CYWM6934 wireless module and the other uses Microchip MRF24J40MA wireless module. Both of them are controlled by Microchip PIC18F series microcontrollers. Communication between microcontroller and wireless module: In order to control the wireless module, microcontroller needs to communicate with the wireless modules. After a study of the datasheets, I find that both wireless module use master synchronous serial port (MSSP) module SPI modes. The SPI mode allows 8 bits of data to be synchronously transmitted and received simultaneously. The advantage of using SPI mode is using the quite few ports to communicate between SPI master and slave. There are four SPI modes. The difference of the fours modes is the clock idle state and sample edge. Both RF module I m using communicate in SPI mode 0,0 which requires that SCK idles in a low state. The communication is between PIC18F microcontroller and RF modules. The diagram below show how SPI communication is done.

2 The microcontroller is the SPI Master and RF wireless module is the Slave. Microcontroller will provide the clock signal to the wireless module. SPI Mode 0,0 SPI mode 0,0 indicates that the control bits state. Below is the different bits state for different SPI mode. In this mode, the control bit CKP=0, CKE=1. The time diagram of the different SPI modes is in the below diagram. SPI MODE WAVEFORM

3 PCB design: The Microchip microcontroller uses onboard programming technology, so I need to design different PCB boards for the different microcontrollers. I have design quite a lot PCBs for the different combination of PIC18F series CYWM6934 and MRF24J40MA. For the CYWM6934, I have designed a PCB using PIC18F2455 to control it.. Schematic diagram Top Layer Bottom Layer

4 For the MRF24J40MA module I have design a PIC18F45J10 development board. Schematic diagram PCB Top and Bottom layers

5 Microchip programming: The new PIC18 microcontroller series allows in circuit program, which means one can program the microcontroller after soldering it onto the PCB board. We use MPLAB ICD2 as the programmer. MPLAB uses the C18 compiler. MPLAB C18 C Compiler is a cross-compiler that runs on a PC and produces code that can be executed by the Microchip PIC18XXXX family of microcontrollers. MPLAB C18 takes standard C statements. Code is written using standard ANSI C notation. Source code is compiled into blocks of program code and data which are then linked with other blocks of code and data, then placed into the various memory regions of the PIC18XXXX microcontroller The MPLAB dialogs and project manager handle most of the details of the compiler, assembler and linker, allowing the task of writing and debugging the application to remain the main focus. The idea of the programming is to make different C functions for different real functionality. For the CYWM6934, I have created the functions below: void delay(unsigned int); void InitialPorts(void); void PowerModule(void); //Power up CYWM chip// void InitialSPI(void);//initialize all the necessary registers void WriteReg(unsigned char address,unsigned char value); void SetToReceive(void);//set CYWM6934 to be receiver void SetToTransmit(void); );//set CYWM6934 to be transmitter void Transmit(unsigned char data);//transmit the data send to this function void Idle(void);// put the CYWM6934 into idle state to save power For the MRF24J40MA, I have created: void bigdelay(unsigned int i); void delay(unsigned int i); void InitialPorts(void);

6 unsigned char ReadShortReg(unsigned char address); unsigned char ReadLongReg(unsigned int address); void WriteShortReg(unsigned char address,unsigned char value); void WriteLongReg(unsigned int address,unsigned char value); void MRF24J40_Enable(void); void Transmit_Frame(void); void Transmit3(unsigned char count); void SleepAll(void);//put both pic18f45j10 and mrf24j40 in to sleep mode void SleepPIC(void);//put pic18f45j10 into sleep mode void SleepMRF(void);//put mrf24j40 into sleep mode void WakeAll(void);//wake up both pic18f45j10 and mrf24j40 void WakePIC(void);//wake up pic24j40 void WakeMRF(void);//wake up MRF24J40 Due to the constriction of the report pages, I omit the detail of the C codes. Conclusion: After a long time coding and debugging, I managed to control both RF modules, I made a comparison between two RF modules. CYWM6934 MRF24J40MA Size Small(24.38mm*16.25mm) Medium(17.8mm*27.9mm) Current consumption Tx Rx both Around 70mA Tx Rx both Around 30mA Data rate Around 0.5KB/Second Around 2KB/Second So my project throws that MRF24J40MA is a better choice. Further improvement: Try to increase the data rate of MRF24J40. I think the speed can be further increased. Reference: Microchip PIC18F2455 datasheet: ww1.microchip.com/downloads/en/devicedoc/39632d.pdf Microchip TM : MPLAB C18 C COMPILER GETTING STARTED f

7

8