Video Timers IOTA-VTI User manual

IOTA-VTI Operation Manual Video Timers
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IOTA-VTI v3.01
A GPS based video time inserter
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.
nclosure 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.

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Obtaining a GPS fix:-
The time to obtain a GPS fix (known as Time To First Fix = TTFF depends on the
condition of the memory backup battery maintained since the IOTA-VTI was last used.
TTFF may be brief (30 seconds if the backup battery is in good condition during the shut
down interval, and the GPS reception is excellent, or TTFF may be several minutes if the
backup battery is flat or was tampered with, or if the view of the sky is not optimal, or if you
have moved large distances since your last use of the unit.
In general, a fix with three satellites will give geographic information, and a fix with
five satellites will provide 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 . (reset to implement the change to take effect . Of course a camera is
required to make astronomical observations.
IOTA-VTI will accept composite video, either NTSC or PAL from a camera and the
(green Camera LED will light to indicate a good video-in feed, and the video out will carry
the camera image as well as overlaid GPS information. The unit automatically switches
between NTSC and PAL input.
For proper operation, the format chosen via DIP position must be the same as the
format used by an external camera.
TV safe area:-
If your output monitor or recorder displays/records only the TV-safe area of video
transmission (such as a regular TV monitor or a video recorder then you should set the
front panel switch to TVsafe. This will place all the information within the TV safe area.
After changing that switch, a reset or power cycle is required for the change to take effect in
the software.
Full screen mode -
some text is chopped off
on a TV monitor.
TV safe mode -
all the text is visible
on a TV monitor.

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Video Screen Types:-
The unit displays a splash screen for a few seconds at startup and is followed by either a
Position screen or Time screen, depending on the setting of the Position/Time switch.
Splash Screen. This gives general credits, the software version (top line , hardware version
(near the bottom of the screen , and an indication of the condition of the backup battery will
be indicated during the interval the splash screen is displayed.
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.
Time screen. This single line display gives GPS fix information, UTC (HH-MM-SS , the
number of 100 microsecond intervals since the most recent 1PPS signal, and the number of
video fields counted since power was applied or the Reset switch was pressed.
The Splash Screen – In Detail:-
The Splash screen (as shown above displays useful information during the startup phase;
- The version of the firmware installed in the device.
- The Author and Quality Assurance origin.
- The Manufacturer.
- The version of the board installed.
- A message that reports on the condition of the Backup Battery since the device was
last used.
The user should note the type of message displayed. There are three conditions:-
- Battery OK - is the normal startup condition. All is well.
- Battery fail - means the battery has failed or the battery was tampered with during the
shut down interval. This will be displayed the first time a new device is used,
because a new device is shipped with a battery insulation tag in place, which of
course is removed after unpacking.
- GPS fail - indicates the firmware failed to communicate with the GPS for some
reason. A Reset or Power on/off/on cycle should restore normal operations.
For more information see the Battery Backup section.

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The Position Screen – In Detail:-
The Position screen displays useful geographic location and some system values you
may find useful. The screen updates every three seconds.
- Satellites: is the numbers of satellites in the GPS fix. The Position screen may
well display more satellites than the time screen can, simply because the time
screen has one character to display the satellite count and the Time screen has
two characters.
- HDOP: (Horizontal Dilution of Precision is a value output by the GPS and is an
indication of the precision of the GPS position information.
o <1 = Ideal
o 1-2 = Excellent
o 2-5 = Good
o >5 = Poor ( inaccurate as much as 300 metres
- UTC: current Universal Time and Date
- Latitude and Longitude: displayed as degrees, minutes, and decimal minutes.
- Altitude: is displayed in metres and referenced to MSL (Mean Sea Level
- 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.
- rr ors: displayed as Transient or Persistent as set by the DIP switch on the
circuit board.
- xt ant/Int ant: is the confirmation that an external GPS Antenna is connected or
not. This message is dependant on the GPS and may not appear with your unit.
- vSync: is an indication of how accurate the clock in your camera is.

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- Internal/ xternal: indicates the source of the V-Sync signals output by IOTA-VTI.
Internal V-Sync signals are generated by IOTA-VTI’s crystal oscillator. External V-
Syncs are generated by a video camera plugged into the Video-IN port. The
“Camera” LED on the front panel echoes this setting.
- PAL/NTSC: is the video format being time stamped.
- 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” as shown
below then the battery was tampered with during the shut down period or is
discharged and should be replaced. See battery maintenance section below.
The Time Screen - In Detail:-
The line at the bottom of the Time screen shows you most of the information you
need for a valid timestamp.
The first character ("F" in this example represents a grade value for the satellite fix.
Item Meaning Details
N No Fix No valid GPS info, NMEA sentences may be
emitted if previous fix data was reliable
X Dead Reckoning fix Based on last real fix. No 1PPS
F Real (1PPS Fix Valid time information (1PPS, GGA , MSL, WGS84
The second character ("6" in this example represents how many satellites have been
acquired. You need at least 5 satellites for a 1PPS timing fix to initiate, and 4 satellites to
maintain the 1PPS fix (timing fix . 3 Satellites or less will stop the 1PPS.
The UTC is next ("21:15:28" in this example . It is updated on receipt of a valid 1PPS
and a GGA NMEA sentence from the GPS.
The numerals "6170" and “6370” are the times (format SS.ssss second of the two V-
Sync signals that occurred during this video frame.
- the V-Sync of the first video field occurred at 21:15:28.6170 UT
- the V-Sync of the second video field occurred at 21:15:28.6370 UT
Lastly we have the field counter, which in this case shows 71094 and 71095. That is
the total number of video fields since power was supplied or the unit was reset. The counter
has been tested to 100 million counts (19+ days for NTSC , at which point the least
significant digit can no longer fit on the screen. Except for that loss of resolution, the
counter will remain valid to 4 billion fields before it overflows to zero.
The Time screen updates every vSync period (20msec PAL, 16.7msec NTSC .

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The Time Screen - Hour Glass:-
If the backup battery voltage is not maintained since previous use, due to battery
discharge or removal, an hourglass symbol will be displayed next to the satellite number.
This is to alert the user that the GPS has lost its backup power and it’s almanac has
reverted to the default status, thereby perhaps losing the correct offset between GPS-time
and Universal Time, therefore time displayed can not be guaranteed.
The absence of the hourglass symbol in the third character position means that the time
displayed is correct to Universal Time.
For information on Almanac Updates and Battery Maintenance, see sections below.
The Time Screen - Loss of GPS fix:-
In normal circumstances, once started IOTA-VTI’s sensitive GPS should keep good
reception to the 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.
IOTA-VTI will display plenty of warning that loss of fix might be imminent by;
- the F, X and N code (see above
- the reduction of the satellite count
Should loss of fix appear likely, and an event is imminent, the user should make a brief
recording of the time screen display, thereby calibrating the field counter to UT, then the
event timing can be salvaged by use of the field counter, which will keep working at all times
the device has power.
Note-1: this condition is unlikely in normal circumstances because, once the GPS has
started, it is very difficult to prevent the GPS from receiving signals. During testing the
IOTA-VTI had to be wrapped in aluminium foil AND placed in a metal toolbox to prevent
GPS reception.
Note-2: If IOTA-VTI is to be used in difficult conditions, e.g. in an observatory with a metal
dome, then the purchase and use of an external antenna that is sited outside the metal
dome is recommended. See External GPS Antenna section for more information.

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The Time Screen – rror Messages :-
IOTA will display on-screen an error message to alert the user that an event occurred
that may affect the time displayed. The message will appear within one second of the event
occurring and will advise of the error type and time of the error event.
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.
The error type and the time of the event are reported at the top of the Time screen
and displays 1 error per line. The meaning of the error is as follows.
rror Name Details
1 UTnotSeq A 1PPS was detected, as well ad GGA information that described
it, but the description was not what was expected.
2 NoPPS A One Pulse Per Second (1PPS was not received.
3 NoGPSmsg No useful NMEA Sentence was received
4 LoopTooLong
The main loop took too long to write the Time message properly on
screen. This is set at 15 msec (PAL and 12.5msec (NTSC .
6 PPStooQuick may occur while the unit is re-stabilising after a Loss Of Signal.
7 NoGGA GGA sentence was delayed. This error will shut down the UT
display for five seconds until the unit has recovered. If it occurs
frequently, reposition the antenna away from sources of RFI.
8 twoGGA Two GGA sentences were received. This will occur in tandem
with and just after a NoGGA error.
9 antAdvis The unit received an unexpected antenna advisory message while
in Time mode
These errors usually represent problems in communication between the GPS unit
and the microcontroller or are induced by an electrically noisy environment.
Note: Error 5 is retired.
Error messages may be set as Persistent or Transient via the setting of the DIP switch.
- Transient means that error messages remain on screen for 5 seconds then are
automatically erased when timing returns.
- Persistent means the error message remains on-screen until cleared by the
operator, by changing to the position screen and back, or by reset.
Time Screen - Almanac Updates:-
If the backup battery supply to the GPS fails or the battery was tampered with during
the shut down period the GPS’s almanac will revert to the default status. The offset between
GPS-time and universal time may be incorrect depending on whether leap seconds have
been added after the GPS manufacture date.
This condition is reported on the Time screen by the presence of the Hour Glass.

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The GPS may take a maximum of 12 min 30 sec of continuous ‘F’ fix for the almanac
to be fully downloaded from the satellites. When download is complete, the UTC may
change by an unexpected number of seconds. The update indicates that UTC has changed
from the logical progression begun at initial acquisition, and is now correct. If this occurs,
information is provided so you can apply an adjustment to UTC to give you the correct time
"before" the update.
If after fifteen full minutes of F fix, the hourglass disappears without an almanac
update shown above, then the default almanac of the GPS was current.
Backup Battery:-
The GPS Real Time Clock and Almanac settings are
maintained by a backup battery, shown in image at
right.
The battery is a CR2032 and should maintain the
backup power for years.
On delivery of a
new IOTA-VTI,
there will be
insulation tag
fitted to prevent
battery use
during shipment.
Simply pull on the tag to activate the backup battery.
The battery condition is advised via the splash screen during start up or reboot. See the
Splash Screen – In Detail section for more information.
If a battery fail message is observed on the Splash Screen and is not a result of activation of
a battery, or known tampering of the battery by yourself or others, then the battery is flat and
needs replacing.
To replace the battery;
- remove IOTA-VTI cover
- remove the old battery and replace it
with the new battery.
- replace the cover.
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.

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Video Frame, Field Type and Frame Central Timing
The video stream has codes to identify an even field type from an odd field type, and IOTA-
VTI can read the field type code and action the 10th millisecond display to put the timing for
the Even field on the Left and Odd field on the Right.
However it is not consistent how video camcorders, video grabbers and DVRs sequence the
field order when assembling video frames. It appears that the sequencing method;
a (even+odd , (even+odd , is the most common
b (odd+even , (odd+even , is somewhat less common
c some will even assemble a pseudo frame from (even+even , (even+even fields, and
actually ignore the odd fields, (or vice versa . Obviously this method is not desirable
because ½ the data the camera sees is tossed away by the recording equipment.
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.
- Using a metal probe e.g. tweezers, as shown in photo above, either the even or
odd fields can be temporarily nulled.
- Probe 5Spare will null odd fields and you will see the right 10th millisecond
display disappear.
- Probe 6Spare will null even fields and you will see the left 10th millisecond display
disappear.
- If during this test you can see only one 10
th
millisecond display and when probing
either 5Spare or 6Spare, it disappears with one probe, and nothing happens when
probing the other, then you know your recording equipment is of the type c above
and is doing you an injustice by throwing away ½ your data.
Finally make a brief recording and examine the 10
th
millisecond display.
- If the earlier time is on the left then your recorder is of the type a above.
- If the earlier time is on the right then your recorder is of the type b above.

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Leap Seconds:-
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.
xternal GPS Antenna:-
The usefulness of an external
antenna will be in those
situations where the IOTA-VTI
v3 must operate at a site that
offers poor GPS reception. The
external antenna, with it’s 5
metres of cable will allow
flexibility to site the antenna to
achieve better reception.
Simply screw the antenna socket
onto the Antenna port on the
rear panel. The GPS will auto
switch between internal and
external antennas
Camera latency:-
Not all video cameras are created equal. Some will send video information just as it
happens. Some will store a complete frame (2 fields and then send the picture information
down the video line. And some will accumulate several frames before updating the video
image.
Your IOTA-VTI does not timestamp the optical image. It timestamps the video
transmission from the camera, and is tested to be correct at the Video In plug on the VTI.
You must determine how much delay (latency there is between a known optical event and
the appearance of that event on the video stream.
The way to tell what your camera does is to point it at the 1PPS LED on the GPS-VTI
and watch the resultant video recording. The LED flashes within 7 microseconds of the
1PPS signal from the GPS, and that's a worst-case scenario; in most cases the LED will
illuminate within 3 microseconds of 1PPS. You want to see just when that flash gets to the
Video In plug. The delay is measured by the subsecond counter on the IOTA-VTI
timestamp.
In the two images below, a GStar-EX PAL camera (an accumulating camera is
viewing the 1PPS LED of a pre-production IOTA-VTI. The camera is set for "no
accumulation." On the left-hand image, the timestamp is at 14:22:00.053, and the 1PPS
LED is still dark. On the right-hand image, the timestamp has advanced to 14:22:00.073,
and the 1PPS LED is now lit. We can safely say that the camera, although set to not
accumulate, still has a one-frame (two field delay between optical event and video
timestamp. This does not mean the camera is useless! It simply means that there is
latency in the system, and any UTC times reported must include the known camera latency.
Thus, if you determine an event occurred at UTC 01:23:45.500 according to the end image
timestamp on the video, then for this camera, the actual end image time is 01:23:45.460
UTC.

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If you see the LED illuminate within one field of UTC change, then your camera
sends video as it happens. If the LED illuminates two fields or more after UTC change, then
the camera is an accumulating camera. YOU NEED TO KNOW how many fields the
camera accumulates before sending the image.
NM A sentence output:-
It is possible to listen in to the NMEA-GGA
sentences from the GPS. This will require use of the
USB Dongle, which in turn requires installation of
FTDI drivers and software like HyperTerminal or
similar.
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.
Conclusion:-
IOTA-VTI will provide you with good, accurate timestamps if you take the time to set
your system up beforehand, and measure your camera latency at the accumulation
settings you use on the night.
Clear skies!
Tony Barry and Dave Gault
Western Sydney Amateur Astronomy Group
Walter Morgan and Sandy Bumgarner - Video Timers