Simple GPS clock for "Garmin 15H-W"

# What's the "GPS clock for 15H-W" !? #
The "GPS clock for 15H-W" is a very accurate handy clock for mobile observation with some intelligent facilities. The clock is operated by referring the GPS (Global Positioning System) signal, so that it can give the time almost as  accurate as atomic clocks give.
If the "GPS clock" is connected via a serial port with a PC, it is possible to monitor the UTC information and geodesic information (Longitude, Latitude,etc.) on demand.

* The GPS receiver "Garmin 15H-W" is adopted. This receiver is very suitable for do-it-yourself.
* The circuit of the GPS clock is shown here. This is constructed by standard parts only.
* You can get an English version of a free software called "Satk" from here. (developed by Takashi Setoguchi.)

GPS receiver Garmin 15H-W	The completed GPS clock --- An example

# Specifications of the "Simple-GPS clock for 15H-W" #
15H-W is operated by 8VDC to 40VDC charge, so that we can use it by connecting it to car batteries (cigar lighter).

=========================================================================================
 Detailed specifications of the "Simple-GPS clock for 15H-W"

Voltage of power supply:	8 V DC to 40 V DC
Accuracy of timing sync.:	within 1 micro-sec
			       *Note: Our experiments show that the LED device has a delay 
				of about 40 micro seconds or so.
Time signal output method:	TTL output, LED beat (flasher), 
				Buzzer output, Audio output
			       *The rising timing of these outputs is synchronized with UTC exactly.

==== via Serial port ====
Serial communications:		A serial link with the GPS receiver is supported. 
				Free software "Satk English version" is usable for this link.
				UTC and Geodesic information are available on demand.
Accuracy of positioning:	within 15 m horizontally, 
				but with a few 10 m error vertically
=========================================================================================

# How to build the "Simple-GPS clock for 15H-W" #

1. You should get GPS receiver "Garmin 15H-W".
The default setting of 15H-W is not good to use GPS clock. You should set it up yourself by utilizing the set-up software "SNSRCFG.exe".

	The recommendable functions for set-up 15H-W
	* Baud rate		4800
	* Position Average	Off
	* PPS mode		1Hz	(indispensable)
	* DGPS Mode		RTCM
	* Earth datum index	WGS84

2. Build up the circuit.
Build up the circuit according to this circuit diagram.
You don't have to construct all of the circuits. Make it according to your required functions.

Built up circuit board of GPS-clock	Connected with PC via serial port

3. Finish. Put it into a suitable box.
Supply a battery and set the GPS antenna on a clearly open place. Wait a few minutes, then the GPS receiver will catch the satellites signals and will emanate 1 pps (pulse per seconds) signals synchronized with UTC.

# How to use the "Satk" on PC #

	Free software "Satk(Satellite Assisted Time Keeper)" is developed by Takashi Setoguchi, Japan. This is the initial window of "Satk". (1) Click the "Set..." button, and the "Setup form"window should appear.
	This is the set up window of "Satk". (2) Choose the "Garmin std" for the "Receiver". (3) If you check "Yes" at "Auto Adjust", the internal timer of your PC will keep accurate time after this. (4) Close the "setup form"window, and click the "connect" button at "Main window"
	An image after the GPS receiver catches the GPS satellites signals. You can get the exact UTC and Geodesic information. However the height information (Antenna) isn't accurate enough. Generally, GPS system is weak in the height measurement.

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