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IOTA-VTI Operation Manual
Tony Barry, Dave Gault, Walter Morgan and Sandy Bumgarner
Preamble:-
The IOTA-VTI is a video time inserter intended for astronomical occultation work. It
takes a PAL (CCIR) or NTSC (EIA) video feed from a camera presumably attached to a
telescope, and overlays the image with GPS-derived time and location information. The
output video feed is sent on to some form of video recording system.
The unit is stand-alone, contains its own GPS unit, and does not require a computer
to function.
This manual is intended for IOTA-VTIv3, with serial numbers 500 onwards or until
further
notice.
Enclosure Front and Rear panels:-
The front panel of the enclosure has two slide switches and three indicator LEDs:-
The rear panel has; a socket for Power, a Dark pushbutton, External GPS Antenna,
a connector for a FTDI serial dongle, and Video In/Out, and a Reset pushbutton:-
Using the IOTA-VTI:-
The unit requires clean 12-volt dc power. Version 1.1.9 will operate over the input
range of 8 to 18 volts, drawing approximately two watts; for version 2.2 and later the
operating range is 8 to 28 volts at one watt. The user must provide a video input signal, and
some form of video monitor and/or recorder.
A backup battery is used to maintain the memory of the GPS during non-use periods.
The condition of the battery is reported by IOTA-VTI systems and for a full description see
the Maintaining Battery Backup section.
IOTA-VTI has an internal GPS receiver, with sensitive antenna, and there is provision
to connect an external antenna. The GPS will switch automatically to the external antenna
when it is connected.
- 1 -
IOTA-VTI v3.01
A GPS based video time inserter
Video Timers
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Summary of Contents for Video Timers IOTA-VTI
- Page 1 A backup battery is used to maintain the memory of the GPS during non-use periods. The condition of the battery is reported by IOTA-VTI systems and for a full description see the Maintaining Battery Backup section.
- Page 2 1PPS information (including UTC and date). Analogue Video Cameras:- A camera is not necessary for IOTA-VTI to display time and position data and it will output PAL or NTSC formatted video according to the setting of switch-1 on the DIP switch (inside the case).
- Page 3 Position Screen. This gives information about the GPS status, the current date and time (to three second resolution), geographic location, and VTI system information. Latitude and longitude are given in degrees, minutes, and decimal minutes. The date the IOTA-VTI was last used is displayed.
- Page 4 WGS84 separation: is the offset (m) between the WGS84 geiod and MSL CPU clock: is the rate of the CPU clock inside the IOTA-VTI’s microprocessor compared to 1 pulse per second (1pps) ticks from the GPS. This should be within 30 microseconds of true.
- Page 5 Fullscreen/TVsafe: indicated the setting of the DIP switch. See “TV safe area” section above. Last used: indicated the time the IOTA-VTI was last used. If the time and date are sensible then the backup battery was able to supply sufficient charge to the GPS during the non-powered state, however if the display is “09’d”...
- Page 6 GPS constellation of satellites. However, if the number of satellites in the GPS fix falls to 3 or less, the GPS will stop outputting 1pps signals, and so IOTA-VTI will stop displaying time and will display ‘x’ shown above.
- Page 7 The philosophy of IOTA-VTI error reporting is to squawk loudly on error, meaning the user is advised within one second of an event that may effect the quality of the timestamp.
- Page 8 Run IOTA-VTI for at least an hour at a site with good reception (5 or more satellites) to ensure the GPS has downloaded the current almanac. You may receive an Almanac Updated message.
- Page 9 IOTA-VTI has the means to demonstrate and identify field type. This is the method; Start IOTA-VTI and display the time screen on a video monitor or similar. Remove the cover to reveal the PCB. Next to the DIP switches you will find two sites marked 5Spare and 6Spare.
- Page 10 At the time of writing, the performance of the GPS receiver during the insertion of a leap- second is not known. However it is imperative that IOTA-VTI be operated for an hour after the insertion of a leap second, to ensure the GPS has updated it’s almanac correctly, and to ensure that the correct time is displayed.
- Page 11 Dark Frame:- On the IOTA-VTI’s Rear Panel, a switch marked Dark can be found. This is to allow dark frames to be made, for subtraction of darks from the recordings. Pressing the switch simply nulls the OSD and can only be activated while switched to the Position Screen. The dark switch will not work while the Time screen is activated.