KorczynskiMcCall

Back to Psych 221 Projects 2013

Active LED Illumination: Wireless Communication

• Active LED Illumination: Wireless Control
• 
  Figure 1. Transmitter
• 
  Figure 2. Receiver

Background

Figure 3

This project idea coincides with several other class projects with regards to experimenting with Active LED Illumination (See References below). Specifically, these experiments involve illuminating objects with high intensity LEDs ( at various levels) to observe and analyze its spectral distribution at high frame rates and various shutter times.

For this project, as further described below, we expect the user to interface our system with the FL3- U3 camera (Shown in Figure 3). We used this camera as a guideline to understand the programming functionality and capability to capture these high frame rate images. This camera acts as a host device that will be programmed to send configuration data (LED module ID # and intensity values) to various LED modules around a room as well as the actual LED Strobe signal to control high density light for high frequencies (in micro-time).

Design Specifications

Our end goal in this project is centered around the following two tasks:

• Enable multiple programmable light sources for experiments like the one shown below, where mutliple LED modules light up a room for an object and are controlled by one single host device.

Figure 4: Room of Wireless LEDs

• Create a synchronous wireless trigger that can handle 500fps (frames per second) speeds. With this design specification, we are expecting the ability to trigger and simultaneously light an LED every 4ms for a specific amount of integration time. Looking at Figure 5, the rising edge of the square wave should simultaneously start both the shutter and LED, then, the LED and shutter remain on for some desired time before ending the shutter and LED flash with the falling edge.

Figure 5: Camera Strobe to LED

For this task, its important to understand the process for how a camera takes a picture with flash lighting (i.e. an LED strobe signal), as shown above in Figure 5. Specifically, the LED flash when timed correctly, can add a lot of balance to the lighting for a photo; however, is the LED flash is out of sync with the camera shutter, then the image ends up being blacked out and disrupted. To verify that the flash appropriately complements the image being captured , it is crucial that the camera timing for the strobe and shutter time line up with the flash LED signal being output. This characteristic is called the synchronization speed; timing plays a very large role in this project because we are trying to obtain images from really high frame rates. The goal is to achieve a 500 frames per second image capture scheme. Since timing is crucial, its important to understand what causes any delay when a signal travels from one end to the other; adding wireless communication on top of that (where signals have to be processed) causes concern for adding unwanted delay. Many cameras today are limited to only that synchronization speeds of the camera Many cameras today are limited to only 1/250 synchronization speeds.

Figure 6: Pulsed Light Distribution

System Overview

Paragraph describing our system, how it works.....

Design

Transmitter

Receiver

Components and Cost (Bill of Materials)

Transmitter

1. Arduino Pro Mini - $9.95 [product]
2. Parallax Transceiver - $39.95 [product] [datasheet]
3. 74AC157 Multiplexer - $0.15 [product] [datasheet]
4. 3 56Ω resistors
5. 2 3-pin headers (0.1" spacing)
6. 3 Green LEDS - [datasheet]
7. Perfboard - $5.95 [product]

Total Transmitter Cost: $56

Receiver

1. Arduino Uno (or cheaper alternative)- $29.95 [product]
2. Parallax Transceiver - $39.95 [product] [datasheet]
3. 74HC138 Demultiplexer - $0.35 [product] [datasheet]
4. 4 150Ω resistors
5. 1 3-pin header (0.1" spacing)
6. 4 Green LEDS - [datasheet]
7. ArduinoShield - $4.95 [product]

Total Reciever Cost: $75 (or $56 with cheaper Arduino)

Design Methods and Execution

Project Exploration

Looking at Xbees

Communication Protocol Definition with Arduino

Creation of custom data packets How do they interact with one another

Transmitter

sends configuration data 5 times (provides margin for error), then switches to LED trigger mode

Software Error Correction

CRC checking

Testing and Camera Emulator

File:DistanceTest.jpg hola

Results

Achieved Specifications

We were able to confirm: distance and delay (synchronization timing)

Tradeoffs

Speed vs Error: Ex. with Xbees

Conclusions

Here is where you say what your results mean.

References - Resources and related work

• PSYCH W13 hardware groups: [Active-LED Based Illumination (Super Cap Flash System)], [Active LED Based Illumination Control]
• Jameco Electronics Catalog ([1])
• The Importance of Flash Sync Speed [2].

Appendix I - Code

Code

Transmitter: Transmitter code for Arduino

Receiver: Receiver code for Arduino

Camera_Emulator: Camera Emulator

Appendix II - Work partition

Design Planning/Schematics: Allison and Corey

Wireless Transmitter Xbee Testing: Allison and Corey

Final Component Selection: Corey

Firmware and Testing software: Corey

Soldering/Assembly: Allison

Presentation and Wiki: Allison