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GPS Monitor

Introduction

With the referencefrequency of PE1FOD and PA3AIN from the March issue of CQ-PA in 2005, which will serve to my counter as a right timebase, I use a Jupiter GPS module TU30-D140. Because the output of 10kHZ is always present, even if no satellites are received, I went looking for a circuit to be able to see that enough satellites are received and there is a so-called lock.

On the site of Dili-Soft , I found a GPS monitor. Initially I used this scheme. Also used the software of that site. Here they use another GPS receiver, which can be programmed which NMEA-line will be in the output. With the Jupiter this is not possible. Therefore I changed the program so that only the line that starts with $ GPGGA is used. Also changed the output to my own wishes.

Jupiter GPS module TU30-D140

This GPS module contains a 20-pin connector. This is a different size. Instead of the usual distance between the pins of 1/10 inch this is 2 mm. With my module I had fortunately a suitable connector. Due to the abnormal size, the flat cable is narrower. Therefore I only soldered the used wires to a 1/10 inch connector.

The connections of the module (see datasheet )
On the diagram that follows later the used connections are shown.

1	Antenna preamp voltage	11	Serial data output port 1
2	5 V power connector	12	Serial data input port 1
3	Backup power	13	Ground
4	3.3 V power connector, not with this model	14	Serial data output port 2
5	Master reset	15	Serial data intput port 2
6	Not connected	16	Ground
7	Protocol selection, Ground = NMEA	17	Ground
8	EEprom selection, to Ground	18	Ground
9	Not connected	19	1-second puls
10	Ground	20	10 kHz signal

Click on photo to enlarge

Diagram GPS monitor

The heart of the circuit is formed by an ATmega8-16. The NMEA output from the GPS receiver is connected tot the RxD input. Only the line that starts with $GPGGA is used. The time, position, number of satellites and the indication that a lock is received are extracted from the $GPGGA-line. The time is in UTC, with switch S2 it can be set to UTC, winter- or summertime. The backlight of the LCD display is on at the start and is switched off about 2 minutes after a lock has been received. With switch S1 the backlight is switch on for about 2 minutes. LED1 is blincking while waiting on the lock and is on when a lock is detected.
The Max232 is used to convert the NMEA TTL level signal to RS232 level, so the signal can be used on a PC with a freeware program such as VisualGPS. Via the ISP connector you can program the ATmega.
Click on the diagram to enlarge or download GPS_monitor.pdf
In the diagram is says 'From timebase (8.2V), present if locked'. This is a connection to pin 7 off U6B, the TLC272 in the above mentioned diagram from PE1FOD.

First test setup:

Click on photo to enlarge

Final construction:

New version (1.5) display, grads and minutes in another format..
Click on photo to enlarge

The program

The program is written in Basic. To build and compile I use BASCOM-AVR. With the demo version you can compile upto 4KB.
The ATmega is programmed in the circuit. For this I use a diagram from Elektuur May 2006. I can't publish this diagram. But there are several diagrams for RS232 or LPT on the web.
I use the program PONY-prog2000 to write to the ATmega. The Fuse bits SUT1 CKOPT are turned on, the rest I left off.
Here you can download the source and the compiled hex file as a 1.3 zip-file or 1.5 zip-file .