Micro-RF Receiver for Bat-Like Robot Final Report ECE445 Senior Design Spring 2015 Zhongzhu Guo, Temitayo Ade-Oshifogun TA: Dennis Yuan Project 62 i Abstract In this project, we aimed to design a micro-RF receiver for the remote control of the movement of a bat-like robot. The receiver platform was built on consumer FM radio product, and due to its unique encoding of control signal, an RF transmitter circuit was also built to pair-up with the receiver. However, due mostly to lack of workforce and lack of time, we were unable to finish implementing the full design within the given time. Nevertheless, we were able to establish the basic communication from receiver host microcontroller to FM receiver IC, collect input samples using Analog-to-Digital Converter, and show functional PCBs with microscopic traces and parts. A List of abbreviations used in this report: ADC – Analog-to-Digital Converter ADC10 – Analog-to-Digital Converter, 10-bit precision ADC12 – Analog-to-Digital Converter, 12-bit precision AWG – American Wire Gauge CCS – Code Composer Studio® DAC – Digital-to-Analog Converter DMA – Direct Memory Access DSP – Digital Signal Processing FCC – Federal Communications Commission FFT – Fast Fourier Transform FM – Frequency Modulation GPIO – General-Purpose Input/Output I2C – Inter-Integrated Circuit I2S – Integrated Interchip Sound IC – Integrated Circuits IEEE – Institute of Electrical and Electronic Engineers ISR – Interrupt Service Routine LED – Light Emitting Diode MCU – Microcontroller Unit MSB – Most Significant Bit PCB – Printed Circuit Board RF – Radio Frequency Rx – Receiver SoC – System on Chip SNR – Signal-to-Noise ratio SPI – Serial Peripheral Interface TI – Texas Instruments® Tx – Transmitter ii Table of Content 1 Introduction...........................................................................................................................................1 1.1 Purpose...........................................................................................................................................1 1.2 Objectives.......................................................................................................................................1 2 Design...................................................................................................................................................1 2.1 Design Procedure...........................................................................................................................1 2.1.1 RF Platform and Controller.....................................................................................................1 2.1.2 Audio Interface with FM IC....................................................................................................1 2.1.3 Signal Encoding and Decoding Schemes.................................................................................2 2.1.4 Firmware Development...........................................................................................................2 2.1.5 Antenna Design.......................................................................................................................2 2.1.6 Precision Clock Source............................................................................................................3 2.1.7 Overview.................................................................................................................................3 2.2 Design Specifications.....................................................................................................................4 2.2.1 Transmitter Circuit..................................................................................................................4 2.2.2 Receiver Circuit.......................................................................................................................5 2.2.3 PCB Design.............................................................................................................................6 2.2.4 Antenna Design.......................................................................................................................6 2.2.5 FM Software Tuning Procedure...............................................................................................7 2.2.6 I2C Multiple Byte Transmission..............................................................................................9 2.2.7 SPI to I2S Interface (For Transmitter MCU only).................................................................10 2.2.8 ADC10 and ADC12...............................................................................................................11 2.2.9 Using DMA...........................................................................................................................12 2.2.10 Control Signal Encoding & Decoding.................................................................................13 3 Verification and Testing.......................................................................................................................15 3.1 Summary of Verifications of the Initial Requirements..................................................................15 3.2 Testing of I2C Interface................................................................................................................16 3.2.1 Debug Run of I2C Communication to Si4705.......................................................................16 3.2.2 Clock Generator I2C Testing.................................................................................................16 3.3 ADC12 Testing.............................................................................................................................17 3.4 Clock Generator Integrity Testing................................................................................................18 3.5 Other Miscellaneous Testing........................................................................................................18 4 Cost Analysis.......................................................................................................................................19 4.1 Labor Cost....................................................................................................................................19 4.2 Materials Cost..............................................................................................................................19 4.3 Total Cost of Development...........................................................................................................19 iii 5 Conclusion..........................................................................................................................................19 5.1 Accomplishments.........................................................................................................................19 5.2 Uncertainties................................................................................................................................19 5.3 Future Work..................................................................................................................................20 5.4 Ethical Considerations..................................................................................................................20 6 References...........................................................................................................................................21 iv 1. Introduction 1.1 Purpose The purpose of project is designing and building a micro-RF receiver for Prof. Hutchinson's prototype bat robot to allow remote control. And if necessary, a specially designed RF transmitter should also be built to match the receiver for sending the required control signal. 1.2 Objectives Goals . Implement a micro-RF receiver to allow remote control; . The receiver should have max PCB area of 2cm2 and max weight of 1.5g, plus an antenna with weight under 6 grams, to be carried by the bat robot. Features Receive wireless RF signal from a commercial or custom-built RC plane controller; Receive at least 2 control signals at the same time (i.e. having at least 2 “control channels”) for robotic movement possibilities; Such RF communication range should be at least 3 meters. 2. Design 2.1 Design Procedure 2.1.1 RF Platform and Controller First of all, the RF platform for remote control is very carefully selected. There are several compelling solutions, among which are Silicon Labs Si47xx FM radio products, Nordic nRF9E5 RF SoC, Linx Tehnology LR-series digital RF transmitter, TI CC3200 SimpleLink Wi-Fi SoC, and even building our custom RF receiver at IC level. Among these solutions, Silicon Labs Si4705-D50 software-tuned FM radio receiver IC is chosen, because it provides the smallest physical size (3x3 mm with minimum external components), good range, and requires minimum RF design. Its drawbacks include low efficiency and non-optimization for remote control application, requiring custom written analog protocol. The Si4705 receiver also requires a host microcontroller (MCU) to operate. Only a selected few from TI MSP430FR5xxx family have desired small size (4x4 mm). MSP430FR5738 is chosen as receiver host MCU, due to its relative high computational performance. 2.1.2 Audio Interface with FM IC The FM ICs have both analog and I2S digital audio interfaces. For transmitter, the host MCU needs to provide audio output. If using analog audio, an external DAC is required, because the MCU has no analog output.