Garmin GPS 16-HVS:

Power requirements: Voltage: 6 – 40 Vdc unregulated

Current: 100 mA @ 6 Vdc

65 mA @ 12 Vdc

28 mA @ 40 Vdc

RJ-45 Connector:

Pin 1 (Red) - Power (+)

Pin 2 (Black) - Ground [Power (-) and Data Return]

Pin 3 (Yellow) - Remote Power On/Off

Pin 4 (Blue) - Port 1 NMEA 0183

Pin 5 (White) - Port 1 NMEA 0183

Pin 6 (Gray) - Pulse Per Second Output

Pin 7 (Green) - Port 2 RTCM SC-104

Pin 8 (Violet) - Port 2 Data Output

RJ-45 Connector (head on view)

Garmin GPS 16-HVS manual:

http://www.garmin.com/manuals/GPS17N_GPS16_17NSeriesTechnicalSpecification.pdf

Configuring the GPS:

The Garmin GPS must be configured using a PC computer before using it with the KIWI. A cable must be constructed to connect the RJ-45 connector of the GPS to the computer’s serial port. The diagram below shows the wiring for the cable:

The power source can be any DC supply between 6 and 40 volts. Once the PC and GPS are connected and powered up, the GPS can be programmed. The purpose of configuring the GPS is to enable the 1PPS signal and to only allow the NMEA sentences GGA and RMC that are needed my the KIWI. Geoff Hitchcox emailed me the program (SNSRCFG.exe) and configuration file (KIWI_OSD.cfg). (See page 3 for his contact information).

Software Settings:

• Run the SNSRCFG.exe program from Geoff

• Select “GPS 16/17” for the Garmin Base Model

• Comm Menu > Setup → Select COM1 serial port and Auto Baud Rate

• File > Open → select KIWI_OSD.cfg → Open

• Config Menu > Sensor Config → Input your latitude and longitude

• Comm Menu > Connect

• The computer will attempt to connect to the GPS

• After successful connect: Config Menu > Send config to GPS (this will upload the .cfg file settings to the GPS)

• All done! Close program and disconnect the GPS.

Connecting the GPS to KIWI:

GPS Pins:

Pin 1 to Power (+)

Pin 2,3 to KIWI ground

Pin 5 to 10k resistor “GPSTX NMEA 4800 8N1”

Pin 6 to Pin 6 of the PIC16F628-20 “GPS 1PPS” RB0

Note: Pin 17 of the PIC16F628-20 (RA0) “1PPS Edge Select” connect to ground

Power Supply:

I used a Vernier AC Adaptor Class 2 Transformer

Input: 120V AC 60Hz 8W

Output: 6V DC 600mA

Connector: 2.1mm jack

The KIWI requires 5V of DC power. The GPS can take anything from 6V to 40V. So, since the power supply outputs 6V, I use a simple voltage divider to get the 5V I need to the KIWI.

Construction:

The KIWI circuit was constructed on a 2½” x 4½” proto-board. Solid core wire was used for most connections. Twisted core wire was used for the GPS RJ-45 connection. The picture below shows the completed circuit:

The circuit is mounted into a plastic enclosure box.

Using the KIWI OSD:

KIWI connected to video in and out and to the GPS:

Initial Setup:

• Turn on the power to the KIWI

• Connect the video input and the video output

• Connect the GPS

• Display:

  • The onscreen display will display “RS232 or 1PPS Absent” at first

  • Then “KIWI OSD V2 FIXWAIT” will be displayed while the GPS attempts to lock onto satellites.

  • The latitude and longitude will then be displayed followed by satellite information

  • UTC date is displayed

  • “KIWI OSD V2 FIXWAIT 1… 2… 3… … 9”

  • UTC time, end of frame time, start of frame time, counter displayed

This is a picture of the official US time from the NIST webpage with the KIWI onscreen display overlaid:

NIST Time

KIWI OSD

UTC time

HH:MM:SS

Field Counter

End of Field time (ms)

Start of Field time (ms)

The bottom of the video screen has this format:

HH:MM:SS EEEE OOOO FFFFFF

where:

HH:MM:SS = Hours, Minutes, Seconds UTC time

EEEE = End of Field time (in milliseconds)

OOOO = Start of Field time (in milliseconds)

FFFFFF = Contiguous field count since initial GPS sync

Note about the INFO Switch:

Geoff notes the function of the INFO switch on his webpage:

After you have finished the timing run, pressing the "info" switch requests that Kiwi OSD wait for the first valid GPS fix - and then compare its internal clock to the GPS. If they agree, a message "PREVIOUS TIMES OK" is displayed on screen. If GPS does not agree, "ERROR: USE FIELD COUNT" is displayed, alerting the user that there has been a previous GPS glitch, and to use the video field count to extract timing information.

Pressing the "info" switch after reading the above summary, gives the OSD chip a RESET, and so another timing run is started.

Example of KIWI OSD in action:

I attempted to measure the acceleration due to gravity with the aid of the KIWI. I took a video of a ball dropped from a certain height. The KIWI allowed me to measure precisely when the ball was dropped and when the ball hit the ground. By knowing the free fall time, the gravitational acceleration can be calculated:

Video frames of the ball drop:

Frame 1

Frame 2

Frame 3

Frame 4

The pictures may not be clear to you. Here is the time for each frame:

Frame 1: 19 38 31 439 422 26701

Frame 2: 19 38 31 506 489 26705

Frame 3: 19 38 31 572 556 26709

Frame 4: 19 38 31 639 622 26713

The distance of the fall is 8 inches or 0.2032m (The distance is measured from the top edge of the ball). In frame #1, the ball is stationary throughout the exposure. In frame #2, the ball has begun to fall. Therefore, I will say the start of the fall occurred at the end of frame #1, so at 19:38:31.439

In frame #4, the ball has made contact with the ground. It looks to me to be at the end of the exposure. I will use the end time for frame #4 as the end of the fall, so at 19:38:31.639

The free fall time of the ball is then: 0.639s – 0.439s = 0.200s

The gravitational acceleration is then calculated by:

The uncertainty in the timing of the frames is half the exposure time. So, for frame #1 the start time is 422ms and the end time is 439ms so the uncertainty is 9ms

So my calculation for the uncertainty in g is:

g = (10.16 ± 0.9) m/s²

The accepted value for g is 9.81 m/s²

My value differs with the accepted value by 3.5%

Although I could have gotten closer to the accepted value by having a greater distance for the ball to free fall, my quick measurement and calculation worked fairly well.

Epilogue:

This manual is meant to give a summary of my work in building this device. I tried to explain the function and use of the KIWI OSD as straight-forward and simple as I could. For a much more detailed explanation on the operation of the KIWI OSD, please visit Geoff Hitchcox’s webpages. He is also extremely helpful through email (see page 3).

Special Thanks to

Geoff Hitchcox

Dr. Michael Richmond

Dr. Linda Barton

Bill VanDerveer