MICRO-RF RECEIVER FOR BAT-LIKE ROBOT TEMITAYO ADE-OSHIFOGUN ZHONGZHU GUO MAY 7 TH, 2015 ECE 445, SPRING 2015

Introduction  Implement a micro-RF receiver for the bat robot to allow remote control of the bat’s movements.  Be able to communicate over a distance of at least 3 meters

Objective of Original Design  Max PCB area of 2cm 2 & Max weight of 1.5g  not including antenna  Receive wireless RF signal from an RC plane controller, either commercial or built by our own.  Receive at least 2 control signals at the same time for robotic movement possibilities.  Communicate over a range of at least 3 meters.

Requirements & Verification

PCB Design  Designed (unnecessarily large) to accommodate service shop constraints & hand soldering…  Only 2 layers, with unplated vias filled by soldering  Bypass capacitors, Vcc&GND planes on bottom, everything else on top  QFN ICs, C0603 capacitors & resistors, C0805 clock generator  External connections using through-hole AWG26 wires  Dimension: Transmitter 44.5 x 26.5mm, Receiver 17 x 12mm  Receiver has 2 versions, Version 2 enlarged to 24 x 15mm + modified trace and holes to help hand soldering, plus reserved space for 1 LED indicator

PCB Design  Left: transmitter PCB; Right: both versions of receiver PCB (to scale)  (1 small square = 1mm)

FM Antenna & Matching

FM Tuning Procedure

FM Tuning: Field Testing (planned)  For transmitter: place antenna close to spectral analyzer input, and check the radiated peaks at 80MHz  For receiver: tune to a local FM radio station, check analog audio output with earphone (need a simple LM386 audio amplifier circuit), or display it directly to oscilloscope; plus, SOFTWARE CHECK received signal quality  SOFTWARE CHECK tuning capacitor value

Control Signal Encoding  Control Signal for bat robot carried in fully separated Stereo Audio  Left = channel selection, Right = current value of selected channel  Transmit 1 channel at a time, channels rotate sequentially  Resembles “Amplitude Shift Keying (ASK)”, but with no carrier...  Sampling rate 48 kHz, limited bandwidth  Internal DAC of FM chips affects “transition edge” when switching channels

Control Signal Encoding  MATLAB simulated response  Worst case: magnitude stabilizes after about 10 samples (plotted below)

Control Signal Decoding  FM receiver IC recovers analog control signal as stereo audio  Receiver host MCU directly reads it from ADC input (10-bit)  Left input volt. tells channel #, right input tells value of the channel  Only accepts stable level

ADC Design  ADC initial configuration  Enable interrupt  Sample and hold clock for 16 cycles  Declare input pins/Set output  Start sampling and conversion  Output configuration  Print output to console  Set LED high when input is above 1.7V

ADC Design Testing ADC Input (V) ADC Output (V, DEC)

I 2 C Master Pseudo Code & Testing

I 2 C Design Master  Set up I2C pins  Enable SWRST to be able to initialize config code  Enable in master mode and set its own and slave address in 7 bit  Select clock, transmitter mode  Define own address and slave address  Enable general interrupts  Enable transfer interrupt  Set start condition and clear SWRST to resume operation  Once slave acknowledges address, start bit goes low and transfer interrupt is set high  Write data into the memory register and set LED high  Print contents of memory register to console to ensure a proper write  Stop condition is set

I 2 C Slave Pseudo Code & Testing

I 2 C Design Slave  Set up I2C pins  Enable SWRST to hold operation to initialize config code  Enable receiver & slave mode  Declare its own address (same as slave address in master)  Enable general, start, stop, and receiver interrupt  Clear SWRST to resume operation  Check for start condition flag meaning master slave and slave’s own address match  Check for receive interrupt to be high meaning that the slave has received the data successfully  Print the contents of the receiver buffer to ensure data has been received properly

I 2 C Results (Temporarily)

I 2 C Transmission to FM Chip

I2C Testing  Screen shot of Code Composer Studio bit-wise debug run  Showed correct Tx Buffer value, slave address, entering correct ISR

Further I 2 C Testing  Ran in step-by-step, bit-wise debug mode in Code Composer Studio  Transmit multiple bytes, Receive single byte both functional  Established connection to FM chips --- correct format & slave address  FM receiver returned “error status” after “power-up” command, BUT… ...Returned normal status after the next “get chip revision” command (?!)  I2C code still have a problem with receiving multiple bytes

SPI to I 2 S Interface

Other Tests Performed  SiT1533 clock generator IC is functional  Continuity tests on PCB: all passed  Receiver MCU: Pin 6 (P1.5) showed NEGATIVE ~0.7V (likely damaged) (This pin is also used by SPI communication to bat robot … … )  Transmitter MCU: Pin 18 (P4.2) ~0.5V when turned ON (likely damaged)

Other Tests Performed  SiT1533 clock generator IC is functional  Continuity tests on PCB: all passed  Receiver MCU: Pin 6 (P1.5) showed NEGATIVE ~0.7V (likely damaged) (This pin is also used by SPI communication to bat robot … … )  Transmitter MCU: Pin 18 (P4.2) ~0.5V when turned ON (likely damaged)

CHALLENGES

Bit-Wise Programming  New to this type of programming for controllers and other devices  Took much time to learn the basics  Energia  I 2 C programming on Energia provided for unknown problems and no debugging help  No step by step implementation of code  Limited availability of Code Composer  Code Composer ineligible for MAC  Unable to access it on the SDL computers  Warnings  Unknown lines of code needed for proper implementation from examples

Challenge: PCB and Soldering  Tough  To get PCB fast, used ECE service shop (assumed to save time...)  However they have constraints: 2-layer, no plated vias, no micro-vias  Modified PCB to fit those constraints (external vias, careful selection of trace & component placement)  Resulted in EXTREMELY hard PCB design... and hard to solder (1 st solder of receiver failed)  Actually wasted time! WOULD be faster if initially ordered 4-layer PCB from off-campus board maker  Hand soldering of microscopic parts: almost impossible (but we made it!)

Further Work  Finish implementing FM chip tuning process  Implement encoding/decoding in software  Implement SPI-to-I2S interface  Full system testing in “real” environment  (If Hutchinson group desire) Make 4-layer PCB to further shrink receiver size down to < 1 sq. cm  Enclose transmitter PCB into a commercial RC plane controller box

Acknowledgements We would like to thanks Professor Carney, Dennis, and Brady for your help, patience, and understanding. We could not have gotten this far without your guidance and motivation. - Temitayo & Zhongzhu