Protocol

Protocol:

Full Detail can be found here on the wiki – http://wiki.everythingrobotics.com/index.php?title=Draft_Proposal

The trigger packet transmitted is 7 bytes long.  Preamble(3 bytes), Sync(2 bytes), trigger command (1 byte) and CRC byte.

The Preamble is used by the the RF module to tune the Receiver.

The Sync word is used by the RF modules receiver circuit to know when a valid transmission is occuring and not just interference.  This SYNC word can be used as a future PAN address, i.e. all your units are set to the same unique SYNC pattern then your units operating in the same area as other trigger units on the same frequency will not be triggered by your units and visa-versa.

If an invalid packet is detected by the CRC then the packet is dropped and the strobe will not fire.  This is where some future work can be done with forward Error Correction, so a corrupt packet could be rebuilt and still used by the slave, i.e. the strobe could still fire even if some corruption is detected.

Currently the slaves so not communicate back to the master in anyway.

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Firmware

Firmware Details:

At the moment it’s pretty basic, but works!  Source is available via SVN (see download page)

The mode is set at powerup by pressing the manual trigger button. If pressed then mode is set to Master, default powerup is in slave mode (i.e.. do nothing). Master mode is identified by a single flash of the LED, Slave is a double flash. This way any of the units can be master or a slave.

Master mode sends a remote trigger command to the slaves when the manual trigger button is pressed, or a trigger signal is detected on the Trigger Input. The LED is light briefly when triggered.

Slaves will only trigger the local strobe if trigger test button is pressed, or a remote trigger command is received via RF. The status LED will light briefly when triggered by either of these means.

The Master will send out a keep-alive broadcast once every 5 seconds. The units LED (master and slaves) will blink briefly to indicated successful RF Link.

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Prototype

Prototype boards RF module Testing

Prototype Specs:

  • PIC16F88 running on internal 8MHz Clock – low cost and very popular, free development tools available, i.e. C compiler.
  • Works in unlicensed 915MHz ISM Band(Australia/US), can work at 433Mhz by changing RF module(US/EU/Australia).
  • RF uses FSK Modulation – Less prone to interference sources.
  • All aspects of the RF module is configurable via the firmware, i.e. frequency, Tx power, receiver bandwidth, modulation, datarate etc.
  • Indoor Range – ~30m+ works all through my house non line of sight, i.e. through multiple single brick walls, with transmitter at furtherest end, close to AV, TV & WIFI (i.e. interference sources) and receiver roaming throughout the house in different rooms, microwave oven also in the mix. No packets lost or dropped so far, but more testing needing to be done.
  • Outdoor Range – Untested, but from indoor tests I would guess 150-250m easily.
    Update:
    Outdoor Test Results here
  • Antenna – Simple 8cm whip (i.e. a single piece of wire), these RF units are matched to 50Ohm so an SMA antenna could be used
  • Sync to 1/125 – in theory it could easily sync upto 1/1000 as the Rf modules are capable of the bitrate necessary, however range will be affected by the higher the speed, also the processor / oscillator arrangement may need to be revised to handle the higher interrupt rate to process data, i.e may need to use a chip with onboard SPI support etc.
  • Can act as Master or Slave.
  • Can be programmed to use any frequency from 902Mhz to 928Mhz (using the 915Mhz module), using the 433Mhz Module will allow similar channels.
  • Can be triggered by a contact closure on Trigger Input. i.e. from camera
  • Can be manually triggered by test button.
  • Trigger output is isolated upto 400V, i.e. can safely trigger old stobe units with high voltage on hotshoe / sync terminals
  • Powered by x3 AA batteries. Currently no power management in the firmware.
  • Cost per prototype board AUD$ ~25

Note on the costs:

  • Most components are sourced via local retail outlets so are probably definately more expensive that sourcing elsewhere, i.e. this can be built a lot cheaper i.e. Sub $10 in parts.
  • Some of the components I had lying around at home so I’ve just used market prices in my estimates.
  • No freight was added to construction costs.
  • Some components have minimium order quanties such as the RF module.

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StrobIt Triggr

Introduction

20/03/09 *UPDATE * This project now has a new home and is actively being developed on Google code project hosting http://code.google.com/p/strobit/

IMPORTANT    This page is no longer being being maintained please go to the new project page.

Welcome to the Strobit Triggr Project, an open source hackable wireless trigger used in photography lighting by using low cost strobe units triggered remotely via RF. This was started while trying to find a cost effective and reliable solution to the commercial alternatives out there. At one end of the market is the Ebay or Cactus Trigger, which is low cost but rather unreliable. At the other end of the market there is the industry standard, Pocket Wizards, very reliable, but very expensive (i.e. way out of my price range).

What I wanted to do was to create an open platform that anyone can easily build for a low cost and then be expand upon by the community. The pair of prototypes I’ve built were a proof of concept that I can get a camera to trigger a strobe unit reliably at a low cost. From early tests it appears that I’ve succeeded in my goal, but further testing is required.

triggr0103

Project Status :

– Prototype successfully working in single master/slave configuration !

– (20/03/2009) Project now has a home at Google Code – http://code.google.com/p/strobit/

Still Todo:

  • Specifications
  • Hardware Design
    • Schematics
    • PCB
  • Software Design
    • Wireless
    • User Interface
    • Protocol
  • Hardware Prototype

License

The strobit hardware design is covered by The TAPR Open Hardware License. Please see http://www.tapr.org/ohl.html for further details.

Schematics:

Strobit Triggr Block Diagram Strobit Triggr Topology StrobIt Triggr Schematic

Prototype Details

Firmware Description

Protocol Description

Downloads – Files associated with the project

Tests – Tests done so Far

In the Wild – Version of this trigger made by others

I’m toying with the idea of putting together a low cost kit for the enthusiast. i.e. PCB, pre-programmed PIC, etc. So we could all benefit with a bulk order of the components. If your interested please email me using the contact form the top menu or use the mailing list signup on the right to give me an indication of numbers interested. Once I finaliaze the design and get some idea of numbers I’ll get a better idea of price. At the moment it will only be available in kit form due to FCC and other Licensing regulations.

Future Improvements:

  • Higher Sync Speed.
  • Frequency Hopping.
  • Forward Error Correction.
  • Power management.
  • UI to change settings, Channel etc.
  • Save settings in Flash memory.