Daredevil Robot Direction Module (DRDM) Senior Design I Midterm Presentation

DRDM Team Kyle Inman Computer Engineer Design prototype Website Software Design Russell Green Electrical Engineer Design prototype Research PCB Layout and Design Dr. Robert Reese Team Advisor Mukul Deshpande Computer Engineer Design prototype Website Serial Interface

Outline Problem Solution DRDM System Overview Constraints o Technical o Practical Approach o Hardware Design o Software Design Progress Timeline

Problem and Solution

Problem Currently, hobbyists and small robotics developers only have access to single direction range finding devices that require the user to perform timing calculations and manipulate trigger signals themselves.

Solution The DRDM will detect obstacles in six directions and transmit proximity and distance information to the user over a serial bus. o User interaction is strictly command based, no trigger pulses required. o All timing and distance calculations are performed for the user. o The module will have configurable measurement modes.

What is the DRDM? The DRDM is an ultrasonic sensor module that will typically be used by a robot. This device will be easily mounted and stackable to fit a variety of platforms.

System Overview The user will command the DRDM over a serial bus. A microprocessor will fire the sensors and time the return signals. The distance data will be transmitted back to the user. User Microprocessor Sensor DRDM

Design Constraints

Technical Constraints TypeDescription RangeThe DRDM must detect obstacles up to 5 meters away and as close as 3 centimeters. Field of VisionThe DRDM must be able to detect obstacles in 6 directions. Power Requirements The DRDM must operate on 5 V power source. Communication Interface The DRDM must support three types of serial interfaces: SPI, I2C, and UART. Update FrequencyThe DRDM must be able to provide an updated mapping within 90 ms.

Practical Constraints Manufacturability The DRDM must satisfy the following dimensions: o Diameter: approx 6 in. o Thickness:approx 1.5 in. The DRDM must also be stackable and mountable in a variety of configurations. o Keeps the device small enough to fit almost any platform.

Practical Constraints Sustainability The DRDM must have a modular design that uses commercially available interchangeable parts. o If a portion of the DRDM malfunctions, it can be replaced inexpensively and the DRDM can continue to function. - Example: one sensor malfunction. o No need for software updates.

The Approach

Approach: Sensor Hardware PIC24 Transmitter Circuit Receiver Circuit Tx Transducer Rx Transducer Send trigger pulse Amplify trigger pulse Convert pulse to energy wave Convert energy wave to electrical signal Amplify return signal and convert to square wave Register return pulse

Approach Hardware: Transducer Choice Option 1: Infrared o Can only detect obstacles up to 3m with limited clarity. o Cannot be used in sunlight. o Requires triangulation to calculate distance. o Size and shape of obstacles can affect the bounceback of the IR signal. Option 2: Ultrasonic o Can detect obstacles over 8m away with clarity. o Can be used in presence of sunlight. o Only requires timing the sonic wave bounceback. o The wave bounces straight back. Decision: Ultrasonic transducers are the more viable option

Approach Hardware: Receiver Circuit The receiver circuit needs to amplify the incoming sinusoidal signal and convert it to a logic level square wave that the PIC24 can register. Solution: Op-amps and a comparator. o Using two op-amps in an inverting configuration amplifies the signal sufficiently. o Comparator can be used to generate a square wave output. o A typical solution for ultrasonic sensors.

Approach Hardware: Transmitter Circuit The transmitter circuit needs to amplify a 40 kHz pulse from the PIC to between 15V and 20V and apply it across the transmitting transducer. Option 1: Op-amps o Would amplify the signal but require high voltage rails to achieve this. o Susceptible to noise. Option 2: MAX232N o Only requires 5V input power. o Can amplify the trigger pulse to almost 20V. o Internal charge pump provides a convenient -10V. Decision: The MAX232N is a better choice.

Approach Hardware: PIC24F This design needs a microprocessor that operates on 5V, can support different serial interfaces, and has multiple timers. Almost every microcontroller can meet these. o The PIC24F family supports all of these. o Has familiar libraries. o Initial testing is being done with the PIC24H family, so the transition will be smoother.

Approach: Software The user will communicate with the DRDM using a serial bus, choosing either I2C, SPI, or UART. The user will then configure the DRDM into one of three measurement modes. 1. Continuous measurement. 2. Measure all sensors on command. 3. Measure individual sensor on command. The software will be split between executing the different modes and processing serial communication.

Approach: Software Software block diagram: Power Up Wait for Init Wait for Mode Config Init command received Execute Mode: Mode dependent Mode command received No Command Process Serial Request Serial Interrupt Mode Change? No Yes

Approach: Software Fire Sensor 40kHz Pulse Wait for Return Shutdown MAX232 Start Timing Return signal Received or Timeout Calculations Stop timer Wait for Request Configure Timers/Interrupts Send Data No Interrupt on Rx pin Rx Interrupt Update Data Output_Ready Last Sensor Fired? Yes No Execute Mode: Fire all sensors on command. Request Received No Request No Mode Change

Approach: Software Best case scenarios: o User sends commands to change modes while the sensors are not firing. o User waits until handshake signal is asserted to attempt to read data. Worst case scenarios: o User wants to change modes while sensors are firing. o User attempts to write invalid command while firing.

Prototype Progress

Progress: Sensor Breadboard

Transducers Max232N OpAmps Comparator

Progress: Testing 40 kHz trigger pulse from PIC Time 10us/div Amplified pulse from MAX232N Initial testing was performed with a constant 40kHz square wave from the PIC24 to demonstrate the circuit could perform as expected. Volts 1 V/div Volts 5 V/div Time 10us/div

Progress: Testing Return signal at comparator output Volts 1 V/div Time 10us/div

Progress: Testing 8 Cycle Input Pusle and Comparator Output Volts 1 V/div Time 500us/div Test Program Output

Timeline January o Research/layout on design o Ordering first round of parts February/March o Breadboard assembly and testing parts o Serial interface programming and testing o Test code for operating sensors March/April o Enhancing sensor hardware: PCB layout o Bring all software elements together End of April o Working prototype

References [1] Eric. Infrared vs. Ultrasonic - What you should know Online: [2] R.Reese, B.Jones, and J.W.Bruce. Microcontrollers: From Assembly Language to C Using the PIC24 Family. Boston, MA: Course Technology, [3] J. Bryant. Using Op Amps as Comparators. Norwood, MA, Online:

Daredevil Robot Direction Module (DRDM) Senior Design I Midterm Presentation