Introduction Gps

8/11/2019 Introduction Gps

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Introduction

A lot of very good information on the GPS system is already available on the net,and is not repeated here. For more see the list withlinks on this site.

Some time ago i managed to get some GPS receiver modules. This is the brains ofa GPS receiver. Such a module accepts an antenna on the input side, and produces

a serial data stream on the output side. This serial output contains information on

the position and speed of the antenna, the exact time, and more details like whatsatellites it receives etc.

These Rockwell Jupiter GPS modules were unused and meant to become part of a

truck fleet management system. Despite the fact that these modules were stockedfor about 3 years, they are still very potent and quite up-to-date receivers with the

following characteristics:

12 channel parallel receiver. The module receives and tracks a maximum of12 satellites simultaneously.

1 PPS output. This means 1 puls per second. This pulse starts exactly at the

UTS second transition. 10 kHz output. An extremely accurate frequency source, for examply to

lock an oscillator as to produce a frequency standard.

NMEA 0183 v.2.01 serial data output with several configuration

possibility's, compatible with all familiar navigation and route plannerapplications, APRS etc.

Sensitive enough to be used with a passive antenna, for example a home-

brew antenna. Separate power supply input for an active antenna. Antenna connector is a standard MCX (OSX) connector, which is often used

in commercial GPS receivers. Antenna's with this connector are readily

available. Extremely well documented. (seedownloads)

Some special properties of this GPS module are:

The interface connector is a somewhat exotic 2mm pitch 20-pin connector.

There is no backup battery for the real-time clock and memory. There is a

place for a super-capacitor. The serial signals are on TTL levels and need to be converted to RS232

levels to be compatible with a serial port of a PC

Because of these properties we designed a support kit. This kit contains a PCBwith components, and has the following specifications:
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Size: 7cm * 11cm, height 2cm incl. GPS module Switching power supply to convert 10-25V input to 5V.

Power supply extensively filtered and protected against overvoltage, pulsesand reverse polarity

Various options jumpers: direct 5V supply or 10-25V unregulated,active/passive GPS antenna, NMEA mode or Rockwell binary mode, 1PPSon RS232 port etc.

Place for 3.6V NiCd battery for long-term clock&memory backup, or 0,22Fsupercap on module for approx 48 hours backup.

The PCB fits in a standard Strapu case (125 * 74 * 27 mm) which is also available.

The Rockwell Jupiter GPS module which can be placed on this PCB is alsoavailable separately, with a supercap and the 20p 2mm connector.

There is also anactive GPS antenna availablethat can be connected on this kit.

Home

Rockwell Jupiter GPS module

Introduction

The Rockwell Jupiter TU30-D140 is a OEM (Original Equipment Manufacterer) GPS

receiver module that is designed to be implemented as part of a larger design, like

a vehicle tracking system, navigational system, time/clock reference etc.

This is a 12 parallel-channel all-in-view receiver. The module is 4 by 7 cm, and has

a 20 pins connector for the various signals and power supply's, and a MCX
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connector to for the GPS antenna.

In order to use the module you do not need very much: a 5V power supply, an

active or passive GPS antenna and a TTL to RS232 level converter to be able to

communicate with the module from a computer's serial port.

The exact specifications of the module are available in PDF format. These are on

the CD if you got it with the module, or can be downloaded from the URL's listed

below.

This article is meant to share the experiences with this module. I do not guarantee

this information to be complete or even correct. Read the Rockwell

documentation on the listed URL's for all details!

Antenna connector

This is a right angle MCX connector, also named OSX. It is not a very familiar

connector amongs radio/electronics amateurs, but is is used in professional rf

designs for cellular networks. Active GPS antenna's are available with this MCX

connector, but more often we see BNC or SMB connectors.

Possibly you got a short piece of 2 mm high-quality coax with a crimped-on MCX

connector with the module. You can use it to make a BNC or SMB adapter cable.

However, some care is needed. When mounting the cable to a BNC connector,

the part of the cable that is not-coaxial should be kept as short as possible, and in

no case longer than 2 cm. If possible, use a crimp-on BNC of SMB connector.

The following is only for the experienced rf amateur. If you have the guts it is

possible to remove the right-angle MCX connector and replace it with another

(SMB) connector or solder a coaxial cable directly to the PCB. The MCX connector

is essentially a surface mounted device. It is soldered on the PCB with 5 points: 4

on the corners and one at the center. When you heat it up, the corners will come

off, but the center conductor is not heated. For the center to come loose you will

have to heat the small tip in the circle at the other side. Do not use force! The

multilayer PCB is absolutely un-repairable.

Antenna

An active (with preamplifier) as well as a passive antenna can be used. The powersupply on pin 1 of the 20-pin connector is put on the center conductor of the MCX


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connector, so you can use either 3.3, 5 or 12V active antenna.

I have done a simple test with a open dipole (just pull apart the screen and center

of the coaxial cable over a distance of 2 * 4.8cm) and it actually works. If you use

a passive antenna, do NOT connect the antenna power supply on the module,

since a passive antenne will short-circuit this power supply! On the cdrom as well

as in the URL list on the end, there are some descriptions of home-brew GPS

antenna. More can be found on the Internet. It's fun to make your own GPS

antenna because of the size as well as the good results. However, keep the cable

as short as possible with a passive antenna, since every bit of signal attenuation

will have direct impact on the quality of the reception and thus also on the quality

of the positioning calculations.

20 pin interface connectorThis 20-pin header has all the power supply, input and output signals exept the

GPS antennasignal. The header has a 2.0 mm pitch, which is not very common. It

is possible to create an adapter using a 2.5"-to-3.5" convertor PCB meant to

connect laptop harddiscs to normal pc's. These can be bought in PC shops for

around 10 euro. This adapter needs some work before you can use it. Some

points are connected together on ground, and some points are not connected at

all. With a sharp knife and some short pieces of wire you can cut away the

unwanted ground connections and make a 1-to-1 adapter. 2mm pitch connectors

are also used for internal wiring in mouse units and floppy disc drives. Another

possibility is to remove the contacts from a ic-socket, the type with tooled bus-

contacts (Augat), and use these to connect wires. Or you can directly solder wires

to the pins or make a special PCB.

20p connector signal description

For the exact and more detailed specifications i refer you to the pdf datasheets.

Pin 1 (square solder island) Power supply for the active antenna. This

voltage is put on the center conductor of the antenna connector. Do NOT

USE it with a passive antenna!! Maximum of 12V @ 100mA. Most of the

active antenna's work at 5V or even 3.3V for the newest types and

consume between 15 and 50 mA. pin 2

Supply for the receiver itself. Should be 5V +/- 0,25V. The receiver

consumes about 200mA. When in MR-active mode (see below) around

100mA. The absolute minimum for the receiver to operate is 4.5V.


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pin 3

Battery backup power input. This 3 to 5V input feeds the static ram and

real-time clock chips of the module when there is no power supplied on

pin 2. Current consumption is then (and only then) between 40uA(3V) to80uA(5V). This voltage is needed to keep the real-time clock running and

static ram contents valid. This is again needed to keep te re-aquisition

time as short as possible. You can use a small NICD or NIMH cell with a

charging circuit, or a goldcap. A lithium cell can be used, but only if the

receiver would be in operation most of the time, since the current

consumption would drain a Li cell in a few weeks. There is an option to

mount a supercap on the GPS board itself. It is explained elsewere on this

page.

pin 4

Slot hole - no pin

pin 5

Master Reset. The receiver is reset if this line is pulled to ground. As long

as the line is 'low' the receiver is in a low-power mode. However, low-

power mode in this case still means a 100mA current consumption.

pin 6, 9 and 14

reserved - do not connect anything

pin 7 & 8

These are digital inputs that define the startup mode of the receiver.

These must either be connected to ground level, of pulled-up with a 10kresistor to +5V

o 7: NMEA protocol select.

When this line is low (ground) the receiver will always start in

NMEA-0183 mode: ascii messages in 400bd, no parity, 8 databits

and 1 stopbit.


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If this line is pulled high the start mode is determined by the state

of pin 8.

o 8: ROM default select.

If this line is pulled to ground the receiver will always start with the

factory default values from the preprogrammed ROM memory.

When this line is high the initial values are taken from static ram (if

a battery was connected to pin 2) or from eeprom. These initial

values include the last known position and date/time, satellite

orbital data, communication parameters etc.

For most of the applications you will want pin 7 to be low and pin 8 to be

high. The receiver will than always start in NMEA0183 mode and uses the

data in sram / eeprom for the initial calculations. See for more details the

datasheet jupiter-gps-board.pdf

pin 10,13,16,17 and 18

Ground. These pins should all be connected to ground.

pin 11 and 12

Serial output (11) and input (12). This is the main serial port over which

the application (pc, laptop, aprs etc) communicates. These lines work on

TTL levels. To be able to talk with a PC you need a ttlrs232 converter

like a MAX232 or a LT1281. Although the rs232 levels officially are

+3..+12V for a "0" or "on" and -3..-12V for a "1" or "off", most of the pc's

and laptops also work fine with 5V and 0V. If you want to try this, all you

need is a 74HCT04 cmos inverter and some passive components. A simplediagram is availablehere.An experimental setup can you seehere.

pin 15

Serial input, also on TTL level. This port is meant for RTCM104 differential

gps correction messages. No special configuration is neccesary - if valid

dgps data is supplied the receiver will adjust its calculations accordingly.

pin 19
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1 PPS (puls per second) signal. This is a TTL signal with a frequency of

exactly 1 Hz. The pulse length is exactly 25.6 ms and the rising edge is

within 1us from the UTC second transition. There is software available

that synchronizes the time in your PC and that expects a 1pps signal on

the DCD line, so if you make an interface yourself you could use this.

pin 20

10 kHz TTL signal. This signal is also synchronous with pin 19 and has a

long-term accurate to 1uHz (microhertz) or better, if the receiver has a

"fix" on the GPS satellites.

The first use of the GPS receiverWhen the module is first used after a long time, do so with an antenna with a

clear sky view. The best program to start with is a simple terminal program like

Hyperterm or Teraterm. Configure the terminal program to 4800bd, no par. 8 bits,

1 stopbit and see if the receiver is producing NMEA data. It should look more or

less like this:

$PRWIRID,12,01.80,11/26/97,0003,*42

$GPGGA,,,,,,0,00,,,,,,,*66

$GPGSA,,,,,,*42

..... etc. ....

When this works you can try a more sophisticated program like VisualGPS or

CSIGPS to see how the reception quality of the GPS satellites is. Depending on a

number of variables it can take a while before the receiver has determined its

position, or has a 'fix on the sky' as it is called in GPS jargon. These variables are:

Was the receiver moved since it was switched off, and if so, how large was

the movement? How long was the receiver switched off

Does the receiver know the exact time+date because pin 3 was fed from a

backup battery, or because a supercap was mounted on the board?

What is the quality of the satellite reception? (number, position and

reception quality of the satellites)

Depending on the answer on these questions the "time to fix" will vary between

20 minutes and 20 seconds. When the energy usage of 1W is not an issue, it is

best to keep the receiver powered on. However, when you use the receiver in a


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car you will want to switch it off, since leaving it on for a few days will most likely

drain the battery.

Installing a Supercap

To keep the Time To Fix as short as possible after power-on, it is possible to installa supercap or goldcap on the Jupiter board. These capacitors have a diameter of

12.5 mm, a height of 7 mm and a pin distance of 5 mm. They are normally

available in the electronics parts stores in capacity's of 0,1F and 0,22F and a

maximum voltage of 5.5V. With a 0,22F supercap the Jupiter can retain it's data

and clock for more than 48 hours, so that the receiver has a much faster fix after

powerup within this time. For a longer backup time an external Nicad or NiMh

battery with a charging circuit will have to be connected to pin 3.

The supercap can be mounted on the Jupiter board on position C2. This positionhas a square solder island and a circular one. The minus of the supercap should be

connected to the circular solder island.

Diagram description GPS support kit

Start with making a paper copy of this diagram. This is a large versionthat can be

printed on a A4 sheet.
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Supply

The GPS interface can be fed in 2 ways: with a stabilized 5V supply or with a 10 to25V unregulated DC supply. In both cases the power is fed into the RJ45

connector on point 8. Pin 7 is DC ground.

The power supply current is first secured with a slow 315mA fuse (in socket).

Then there is a Transzorb device to ground. This device is a short-circuit forreverse polarity voltages and for voltages above 27V. It causes the fuse to blow

and in doing so, protecting the other electronics and GPS module.

After the Transzorb there are several other components for filtering and theunregulated voltage is supplied to the switching regulator U2. This LT1107CN8-

5(datasheet)produces 5V without much heat losses. A linear regulator like a 7805

would dissipate approx. 2 Watts. With this switching regulator the dissipation islimited to max. 0,3Watts. R10 defines the output voltage. If it is 0 ohm, the output

voltage would be exactly 5V. We chose to make it 5k6 ohm so the output voltage

becomes approx. 5,1V. This is done to compensate for the loss in the filter aroundL3. R9 is only used when you use the adjustable version of the LT1107, and since

we supply the fixed 5V output version, this position stays unpopulated.

The regulated 5V is then wired to the 2-position jumper SW5. With this jumperwe can choose between the 5V from the LT1107 regulator (position 2), or from anexternally supplied 5V regulated supply (position 1). After this jumper ther is an

additional Transzorb to ground. This one short-circuits everything above 6V. Ifthe SW5 jumper is in position 1 (external 5V) and a higher voltage is supplied, thisTranszorb burns the fuse end protects the sensitive GPS module.

After some more filtering (C6, L3, C7, C8) the +5V is offered to the GPS module

and the RS232 converter. There is also a simple charging circuit consisting of D6,D7 and R6 for an optional NiCd battery to keep the real-time clock and static ram

of the GPS module powered, as to speed up locking to the GPS constellation after

power-up. However, we chose to not deliver this NiCd battery and instead offer a0,22F 5,5V supercap, that can be soldered directly onto the GPS module. This

supercap keeps the clock running for approx. 2 days. If you want longer retentionyou will have to mount a 3,6V NiCd PCB-mount battery, for example the

Emmerich NC-M120-3,6V type, or any other 3,6V NiCd or NiMH type. You can

also choose to use a non-recharable 3V Lithium cel. In that case, do not mount thecharging circuit or disconnect it from the battery.

Via jumper SW4 and a 10 ohm series resistor R7 5V is offered to the GPS moduleto feed an external active antenna. When you use a passive antenna, leave SW4

open.
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RS232

The GPS module outputs a serial TTL (0V / 5V) signal. This must be converted toRS232 levels (+5 to 15 / -5 to 15V) before it is usable by the PC host computer.

The RS232 level convertor is the conventional circuit around a MAX232 (U1).The 4 converters in this chip are all used: 2 for the NMEA serial data input andoutput port, 1 output to convert the 1PPS signal to RS232 levels and 1 input for

connecting an optional differential GPS receiver.

The 1PPS signal can be connected to either pin 1 (DCD), pin 6 (DSR) or pin 8(CTS) of the serial port.

Software like NMEAtime or Linux time server can use this 1PPS signal to achievea a very accurate time synchronisation. Every software package has its own way

of detecting this 1PPS signal, and some softeware packages don't use it al all.Therefore the 1PPS signal is configurable on pin 1, 6 or 8 of the DB9 connector. Ifthe software you use does not make use of this option, than don't wire anything at

all.

The DB9 connector is wired as a modem. If you have an existing modem cable itcan be used to connect the GPS kit to the serial port of the PC or laptop.

All signals are also wired to the RJ45 connector, so the DB9 female PCB

connector is in fact optional when filling the PCB with components. However, youwill need to make your own cable.

RJ45 connector


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For the power supply and variuous other signals a RJ45 connector with 8 contactshas been chosen. This is a much-used and robust connector. The disadvantage isthat you need a special crimping tool and special cable tou correctly mount a

cable. These tools are available for prices of around 10-15 Euro. For a small fee

we can supply you with some cables that enable you to make your own cable. But

you can also buy a UTP network cable at the local PC shop. Make sure you buy a

network cable with all 8 contacts wired!

The pinout:

contact direction level description.

pin 1 output RS232 1 PPS signal on RS232 level. Locked on GPS timebase.

pin 2 output RS232 NMEA data port output..

pin 3 input RS232 NMEA data port input.

pin 4 output TTL 10kHz squarewave locked on GPS timebase.

pin 5 input RS232 2nd serial port for optional differential GPS receiver.

pin 6 output TTL1PPS signal on TTL levels, directly from GPS module. locked on

GPS timebase.

pin 7 ground 0 Volt common, for both the RS232 port and for the power supply.


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pin 8 power+5 or

+10..+25Vdepending on the position of jumper SW5.

The TTL signals are directly connected to the GPS module.

JumpersJumper function position position remark

SW1 RESET 1=reset active 2=normalpin 5 GPS

module

SW2

boot mode NMEA

mode 1=start in NMEA mode

2=start determined by

SW3

pin 7 GPS

module

SW3boot mode ROM

defaults

1=start from ROM

default

parameters

2=start parameters

from Sram/EEprom

pin 8 GPS

module

SW4 Antenna supplyjumper on = 5V active

antenna

jumper off = passive

antenna

pin 1 GPS

module

SW5 input power selection 1=5V regulated 2=10 to 28V unregulated

PS-

1/6/8

1PPS rs232 output

selection

wire PS-1 = 1PPS on CD

wire PS-6 = 1PPS on DSR

wire PS-8 = 1PPS on CTS

see remark

Wire jumper for connecting 1PPS signaal to DB9. When you use NMEAtime

for time synchronisation of your PC you will want to connect the hole

marked "PS" and 1, 6 or 8. Examine the software manual to learn about

the details.

Home

Testing the build kit

After the PCB has been build we need to do some tests, before the GPS module isplaced.
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Power supply

First of all, the jumpers should be set in these positions: RESET in pos. 2, NMEAin pos. 1, ROM in pos. 2, place ANT jumper and place SUPPLY jumper in pos. 2

because we test on 12 Volts.

You also need to make a cable for connecting the power supply on pin 7 (ground)

and pin 8 (+ supply) of the RJ45 connector. See thecablingpage for details.

Connect 12V on pin 8 and ground on pin 7 of the RJ45 connector. The LEDshould light (there is only 1mA running through it) and you should measure the

following voltages between ground and:

pin 2 and 3 of the LT1107: +11,3Vpin 8 of the LT1107: +5,0Vpin 2-3 of the Supply jumper: +5,1V

pin 16 of the MAX232: +5,1Vpin 6, 14 and 7 of the MAX232: -9,5V

pin 2 of the MAX232: +9,5V
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The power supply and rs232 level converter are now tested. You should be able to

vary the input voltage between 10 and 25V, and the 5V and 9,5V should remainstable. Do not increase the input voltage above 27V since the input transzorb will

start conducting and blow the fuse!

Remove the power supply and put the GPS module on its place over the 4 PCB

supports. Don't foret to remove the hooks of the plastic PCB supports, since it will

be extremely difficult to remove the GPS module if you don't. While inserting,

watch the 20-pin connector to slide smoothly into the connector on the PCB.Further tests should be made with the GPS module and an oscilloscope or a serialconnection to a PC.

When you use the GPS kit on a 5V power supply, for example by feeding it via the

Y cable from the USB or mouse port of your laptop, chack the voltage on themodule (pin 2 of the 20-pin connector). It should be between 4,75 and 5,25V. TheGPS module will not work below 4,5 V.

The very first tests can best be done by watching the NMEA data that is sent out to

the serial port. Use the standard Hyperterm windows application or even better:installTeraterm. Communication is default done with 4800bd in readable ascii

tekst en can be read quite well, if you recognise the patterns.

When the module is connected for the first time after a long period it should be

done with an external antenna and a clear view on the sky. Use Hyperterm orTeraterm and set it for 4800bd / no par. / 8 data / 1 stopbit to see if the receiver

generates NMEA data. It should look like this:

$PRWIRID,12,01.80,11/26/97,0003,*42

$GPGGA,,,,,,0,00,,,,,,,*66

$GPGSA,,,,,,*42

..... etc. ....

When you see this pattern you can start another application like VidualGPS or

CSIGPS to see how the reception of the GPS satellites is. Depending on a number

of variables it can take a while before the receiver has determined his ownposition. These variables are:

Was the receiver moved since it was last shut off, and how much was this

movement?

How long has the receiver been powered off?

Is the receiver aware of the current date/time, because pin 3 (Vbackup)

was kept powered, and/or there was a supercap mounted on the GPS

board itself?

What is the quality of the satellite reception? (number, position and signalstrength of the satellites)
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Depending on these variables it can take somewhere between 20 seconds and 20

minutes before the GPS receiver is transmitting valid position data.

Home
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Documents

Introduction Gps