Synchronized Strobe for Video Camera Jeff Baskett & Jason Zubo Project Advisor: Dr. Irwin

Contents of Presentation Project Summary Strobe Light Microprocessor DMX Interface Video Camera Hardware Results Problems Encountered Unfinished Work

Project Summary We are designing a circuit to control a DMX512 strobe that will be synchronized with the shutter on a video camera. Based on the shutter speed of the camera, we plan to fire a strobe during each frame to freeze high-speed motion preventing any blurring effects. This project is for the mechanical engineering department to aid in research involving fast moving fluids.

Block Diagram Reflected Light Viewed Image Sync Pulse Circuitry Video Recorder Sensor Power Compensation Strobe Rs-485 Interface Microprocessor Image

Block Diagram Reflected Light Viewed Image Sync Pulse Circuitry Video Recorder Sensor Power Compensation Strobe Rs-485 Interface Microprocessor Image

Strobe Snapshot DMX/D –Requires differential input of DMX512 signal –Will operate in DMX mode where intensity is the first byte of data received, the duration will be preset and the rate will be determined by the refresh rate.

Standards

Block Diagram Reflected Light Viewed Image Sync Pulse Circuitry Video Recorder Sensor Power Compensation Strobe Rs-485 Interface Microprocessor Image

Microprocessor (DMX Interface) Increment or decrement strobe intensity based on output from power compensation circuitry. Use preset duration value (found experimentally) to maximize strobe effectiveness. Output appropriate DMX signals to strobe at 250Kbaud.

Microprocessor (DMX Interface) The rate is determined by DMX refresh –The strobe will fire at the end of a packet of data Sample packet of data (RS-485 levels) Break - 88us Mark after break - 8 us Start code - 44us Start bit for data Stop Bits for data Idle line Intensity Data Duration Data

Software Flowchart

Microprocessor Timing circuitry and DMX interface will be implemented in software. Serial data will be designed to meet DMX-512 standards. UART will output serial data to RS-485 interface. Output (TTL levels) must be inverted (RS-485 levels). Additional data packets were sent due to DMX addressing problems.

UART UART will output data at an extended rate of 250 Kbits/sec. Data will be accompanied by one start bit and two stop bits UART implementation requires Mod515.inc header file

DMX Output

Block Diagram Reflected Light Viewed Image Sync Pulse Circuitry Video Recorder Sensor Power Compensation Strobe Rs-485 Interface Microprocessor Image

RS-485 Circuit

Block Diagram Reflected Light Viewed Image Sync Pulse Circuitry Video Recorder Sensor Power Compensation Strobe Rs-485 Interface Microprocessor Image

Video Camera Sony XC-75 CCD Black and White Video Camera Module –On loan from ME department –Sync output was not functional - embedded in video signal

Block Diagram Reflected Light Viewed Image Sync Pulse Circuitry Video Recorder Sensor Power Compensation Strobe Rs-485 Interface Microprocessor Image

Sync Pulse Circuitry Converts Video signal into sync signal Uses Precision Rectifier, inverter and Schmitt Trigger

Sync Pulse Circuitry Video SignalSync Pulse Sync Pulse is used to trigger software interrupt to output Dmx data to fire strobe

Block Diagram Reflected Light Viewed Image Sync Pulse Circuitry Video Recorder Sensor Power Compensation Strobe Rs-485 Interface Microprocessor Image

Sensor We are using a photodiode with a current to voltage converter to sense the light output from the strobe

Sensor Circuit Added a low pass filter to clean up output of the photodiode circuit

Block Diagram Reflected Light Viewed Image Sync Pulse Circuitry Video Recorder Sensor Power Compensation Strobe Rs-485 Interface Microprocessor Image

Power Compensation Window Detector –This determines the need to increase or decrease the intensity of the strobe –The measured value of intensity from the sensor is the input and is compared to ideal intensity levels which were determined experimentally –The output is a signal denoting the need to increase or decrease the intensity

Window Detector

Results System is functional minus power compensation We are able to view stop-motion effects We performed several experiments to show functionality

Experiments Performed with and without synchronized video strobe –Light Bulb breaking –Spinning Wheel –Spinning Football –Spinning Frisbee –Golf Swing

Light Bulb - Room Light

Light Bulb - With SVS

Water Drop - Room Light

Water Drop - With SVS

Spinning Football - Room Light

Spinning Football - With SVS

Spinning Frisbee - Room Light

Spinning Frisbee - With SVS

Golf Swing - Room Light

Golf Swing - With SVS

Problems Encountered UART troubles DMX Inversion Number of DMX data packets to send Expo troubles Inconsistency of Strobe

Strobe Inconsistency Strobe was designed for theatre and stage show usage - not for precision Delay between receiving data and firing varies by about 15 ms

Work in Progress Purchase more precise strobe Integrate Window Detector into system Eliminate EMAC board - Place software on to a programmable chip

Questions?