USBFlashTrig

This project provides the ability to control a remote triggerable camera and an accompanying light for computer controlled image capture.

Overview

The USBFlashTrig system consists of 3 layers and 4 parts:

• a linux kernel module or a userspace libusb program
• a controller
• a hardware interface board

Kernel Module

The kernel module must be compiled and loaded by executing

cd src/module
make
sudo make load

As part of the USB Subsystem on Linux the kernel module will automatically assume ownership of any connected flashtrig controller and provide the following files in sysfs:

• trigger
  • (W) triggers the camera to take a picture
• flash
  • (W) starts the flash and triggers the camera
• light_on
  • (W) turns on the flash light
• light_off
  • (W) turns off the flash light
• light_state
  • (R) represents the current light state, on or off
• flash_time
  • (R/W) the time of the flash light to be on when flashing

Trigger, flash, light_on and light_off accept any input:

echo 1 > trigger
echo asdjhaksjdhaksjdh > flash

light_state and flash_time can be read and return the set values:

cat flash_time % return e.g. 500 meaning 500ms
cat light_state % returns [0|1], depending on the light state [off|on]

The flash_time can be set with:

echo 20000 > flash_time

this turns the light on for 20 seconds, when flash is executed.

Userspace libusb program

This userspace utility allows control of the FlashTrig controller without sysfs, and serves as an example on how to integrate it into other programs. It consists of a C++ class FlashTrig.cpp for the FlashTrig controller and a corresponding argument parser control.cpp. The program needs r/w rights on the controller (e.g. sudo) To compile:

cd src/commandline && make

For usage:

./flashtrig --help

Controller

The controller is a modified usbasp. To flash the firmware:

cd src/device
make
sudo make flash

It uses interrupt timers to achieve 1ms resolution on the flash time, up to 65.535 seconds. The control with the host pc is accomplished using the V-USB library from OBdev and one usb control endpoint.

Hardware interface board

This board is effectively the driver stage of the controller. It has a resistor arrangement to remote trigger a Panasonic GH-2 and a power MOSFET to control the power line of a DC-powered light.