Synchronized Strobe for Video Camera

Jeff Baskett & Jason Zubo

Project Advisor: Dr. Irwin

Contents of Presentation

• Project Summary

• Standards

• Project Description

• Parts List

• Schedule of Tasks

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.

• The only inputs into the system will be the video synchronized signal from the camera and the intensity of the light read by the sensor.

• The outputs will be the intensity of the light from the strobe.

• The recorded image will be analyzed to determine the

effectiveness of the system.

Standards

Block Diagram

Reflected Light

Video Recorder

PowerCompensation

Timing Circuitry

Strobe

Sensor

Light input

Video input (reflected light)

Viewed image

Light

Image

DMXInterface

SynchronizedSignal

Timing signal and 250K clock

IntensityAdjustment

Block Diagram

Reflected Light

Video Recorder

PowerCompensation

Timing Circuitry

Strobe

Sensor

Light input

Video input (reflected light)

Viewed image

Light

Image

DMXInterface

SynchronizedSignal

Timing signal and 250K clock

IntensityAdjustment

Video Camera

• Sony XC-75 CCD Black and White Video Camera Module– We will have to determine from where in

the camera we will get the shutter signal

– The input to the camera will be the reflected light from the image

Block Diagram

Reflected Light

Video Recorder

PowerCompensation

Timing Circuitry

Strobe

Sensor

Light input

Video input (reflected light)

Viewed image

Light

Image

DMXInterface

SynchronizedSignal

Timing signal and 250K clock

IntensityAdjustment

Timing Circuitry

• Delay Circuitry to insure strobe fires during time when shutter is open. – This delay will be calculated and implemented

with an RC circuit

• 250 KHz clock signal– This will be used to shift the bits of data to the

strobe at the necessary 250 Kbaud rate as specified by DMX

– This will be implemented using a 555 timer

Block Diagram

Reflected Light

Video Recorder

PowerCompensation

Timing Circuitry

Strobe

Sensor

Light input

Video input (reflected light)

Viewed image

Light

Image

DMXInterface

SynchronizedSignal

Timing signal and 250K clock

IntensityAdjustment

Sensor

• We will be using a photodiode to sense the light output from the strobe

• Circuit design for converting photodiode output to useable levels has yet to be explored

Block Diagram

Reflected Light

Video Recorder

PowerCompensation

Timing Circuitry

Strobe

Sensor

Light input

Video input (reflected light)

Viewed image

Light

Image

DMXInterface

SynchronizedSignal

Timing signal and 250K clock

IntensityAdjustment

Power Compensation

• Window Detector– This will determine the need to increase or

decrease the intensity of the strobe– The measured value of intensity from the

sensor is the input and will be compared to ideal intensity levels which will be determined experimentally

– The output will be a signal denoting the need to increase or decrease the intensity

Block Diagram

Reflected Light

Video Recorder

PowerCompensation

Timing Circuitry

Strobe

Sensor

Light input

Video input (reflected light)

Viewed image

Light

Image

DMXInterface

SynchronizedSignal

Timing signal and 250K clock

IntensityAdjustment

Strobe

• Snapshot DMX/D– Requires differential input of DMX512 signal– Will operate in DMX mode where intensity is

the first byte of data received, duration is second, and the rate is set by DMX refresh

Block Diagram

Reflected Light

Video Recorder

PowerCompensation

Timing Circuitry

Strobe

Sensor

Light input

Video input (reflected light)

Viewed image

Light

Image

DMXInterface

SynchronizedSignal

Timing signal and 250K clock

IntensityAdjustment

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 using 250Kbaud timing clock.

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

Break - 88us

Mark after break - 8 us

Start code - 44usStart bit for data

Stop Bits for data

Idle line

Intensity Data

Duration Data

DMX Interface

64-bit Shift Register

DurationPresets

StopBits

IntensityCounter

250 KBaud clock Differential DMX-512 output to strobe

Power Compensation Output

StartBits

64-bitCounter

RS-485Interface

DMX Interface

64-bit Shift Register

DurationPresets

StopBits

IntensityCounter

250 KBaud clock Differential DMX-512 output to strobe

Power Compensation Output

StartBits

64-bitCounter

RS-485Interface

DMX Interface

64-bit Shift Register

DurationPresets

StopBits

IntensityCounter

250 KBaud clock Differential DMX-512 output to strobe

Power Compensation Output

StartBits

64-bitCounter

RS-485Interface

DMX Interface

64-bit Shift Register

DurationPresets

StopBits

IntensityCounter

250 KBaud clock Differential DMX-512 output to strobe

Power Compensation Output

StartBits

64-bitCounter

RS-485Interface

DMX Interface

64-bit Shift Register

DurationPresets

StopBits

IntensityCounter

250 KBaud clock Differential DMX-512 output to strobe

Power Compensation Output

StartBits

64-bitCounter

RS-485Interface

DMX Interface

64-bit Shift Register

DurationPresets

StopBits

IntensityCounter

250 KBaud clock Differential DMX-512 output to strobe

Power Compensation Output

StartBits

64-bitCounter

RS-485Interface

Tradeoffs• Large shift register and counter would be difficult

to implement and control.• Microprocessor is capable of controlling timing of

data as well as transmission of data.• Window detector output will interface directly

with a microprocessor without A/D conversion, thus eliminating round off error.

• Software will make the project easy for future students to modify or add features.

Microprocessor

• Interrupt driven timing control of data to follow DMX 512 standards

• Will output serial data to RS-485 interface as shift register would

Parts List

• Strobe - Snap Shot DMX/D• Video Camera - Sony XC-75 (in stock)• RS-485 Interface - MAX1480C• Sensor - EG&G Vactec PhotoDiode (in stock)• EMAC Evaluation Board (in stock)• Sensor amplification-AD823 dual precision,

16MHz, operational amplifier. LM741 dual in-line operational amplifier. (in stock)

Schedule of Tasks

• Finish project by Student Expo

• Other than that, we’re not sure how long things will take.