Constructing and Installing GPS Umbilical Cord
The GPS Umbilical cord connects the uBlox GPS module (external to the orb), to the aggregator. It carries 2 serial signals (a TX signal and an RX signal), GND and a regulated 5V power from the aggregator. On one end it is soldered directly to the uBlox GPS module; on the other end there is a little micro-connector that plugs into a mating connector on the aggregator. In-between there is a breakaway connector that allows the GPS stalk to break off the orb axle without dragging along by the umbilical cable.
The cord is constructed from a recycled mini-DIN-6 cord that was probably used in a past life to connect a keyboard to a PC. Turning it into the umbilical involves cutting it into two pieces, one being roughly half the length of the original cable (long enough to reach from the end of the axle, thru the axle, and up into the aggregator with some slack for steering), and the other being long enough to reach from the GPS module down the stalk to the connection point with the axle. The free pigtail ends are soldered to the GPS module and aggregator micro-connector, while the connector ends mate at the connection point of the GPS stalk and orb axle. The female half of the cable is on the orb, the male half of the cable is on the GPS stalk.
4 connections need to be made on each end of the cable: GND, 5V, TX and RX (beware - the TX and RX are confusing... will try to be unambiguous).
GPS Module (with underside of module oriented right-side up, with wire-in connections at left):
- GND: At the bottom of the row of solder holes is a pair of holes for VCC and GND. Solder the BLACK wire of the umbilical cord to the GND connection.
- VCC 5V: At the bottom of the row of solder holes is a pair of holes for VCC and GND. Solder the RED wire of the umbilical cord to the VCC connection.
- TX GPS to AGG: At the top of the row of solder holes is a GND hole. Just below that (2nd from the top) is the TX-out of the GPS module. To this point, solder the YELLOW wire of the umbilical cord.
- RX AGG to GPS: The next hole down (3rd from the top) is the RX-in of the GPS module. To this point, solder the GREEN wire of the umbilical cord.
Aggregator: We have some micro-connector patch-cables that came with the old GPS modules. Seek one out and cannibalize one such patch-cable (ribbon-cable), cutting it in half.
- GND: The black wire of the micro-cable is GND. Solder it to the BLACK wire of the umbilical cord.
- RX GPS to AGG: The __(white?)__ wire of the micro-cable is the Agg RX. Solder it to the YELLOW wire of the umbilical cord.
- TX AGG to GPS: The __(green?)__ wire of the micro-cable is the Agg TX. Solder it to the GREEN wire of the umbilical cord.
- VCC 5V: The umbilical 5V connection DOES NOT go into the micro-cable. It receives a 5V tap from the DB9 cable that comes from the SPU. This wire is ORANGE in the DB9 cable. Seek out this orange wire from the DB9 cable and solder a short patch wire to it. Solder another short patch wire to the RED wire of the umbilical cord. Then place mating halves of an in-line connector on the two patch wires, and plug them together.
Having all connections between the umbilical cord and aggregator connectorized means we can separate the aggregator from the umbilical cord, which is what we want.
If no TX/RX works, try examining the pinout of the old GPS module relative to the colors of the micro-cable, and check to make sure you've got the right wires. Or just try swapping the colors above and see if that does it.
If there's bad TX/RX and bad power (you can't see 5V at the GPS module), try jimmying the mini-DIN-6 connector. If this causes intermittent voltage, you've got a bad connector (worn-out contacts?) and should start over.
Note - It would be nice if all GPS stalks were interchangeable among the orbs (rather than having stalk-1 only work with orb-1). Since we're recycling pre-assembled mini-DIN-6 cables, it's not certain that the wire insulator colors are consistent with regard to which pins in the DIN connector they are assigned to. For this reason, whoever constructs the batch of GPS umbilical cords might want to either confirm that all cables they're building have consistent color schemes, OR do the wiring such that the DIN pins are consistent, rather than the insulator colors.