Rockwell Jupiter GPS module


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 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.


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

This 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.

The first use of the GPS receiver

When 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:

..... 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: 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 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 install a 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 position has a square solder island and a circular one. The minus of the supercap should be connected to the circular solder island.