GPS Receiver - UP500

Fig. 1 GPS receiver

Description:

This board is a GPS receiver. It is based around a Fastrax UP500 receiver and interface with a processor board with a serial port. The default protocol is NMEA, 9600 baud, with 8bits, no parity and 1 stop bit.
An on board supercap provides backup voltage to the receiver for quick fix. It can provides backup for up to 48h. After this, the board would do a cold start.
The board interface is an 8 bits type. A set of jumper can select either bit 1 and 2 (PIC16F628 type) or 6 and 7 (PIC18F2320 type) for Rx and Tx connection. Bit 0 provides an optional 1 pulse per second signal.

The board can be powered by 3.3 or 5V processor board.

Schematic:

The power supply is filtered by R3/C1, and C2, charged by D1, provides backup voltage. R1 and R2 offer some protection for the Tx and Rx signal. JP1 allows to select between bits 1-2 or bits 6-7 for these signals. It allows to connect easily the board to PIC16F628 or PIC18F2320 processor boards. JP2 connects the optional 1PPS signal from the GPS receiver to pin 0 of the interface bus.
R5 is here to have an easy Gnd point to connect a test instrument.

Fig. 2 GPS UP500 schematic

Construction:

The PCB fits on a small single sided board. All components are on the top side.

Fig. 3 GPS UP500 layout

Start with the lowest components, and continue with the higher ones. Keep the GPS receiver for last. Solder the 6 pins pinheader to the pcb board.
R5 is made up of a piece of resistor's lead. It's here to easily attach a clip from a test instrument or have a Gnd test point.

Once all the components are soldered, you can test the board as described below and GPS1 can be fitted. Put it on the pinheader and solder it.

Pads 1 to 4 can be drilled to 3mm to fix the board, or put spacers.  

How to use / Testing:

To check the board, connect the board to an 8 bits interface and power up the board. Check you have the Vcc supply on pin 4 and 5 of pinheader.
Switch the power off and check that pin 5 of pinhead still have power, for backup.
To check you get a GPS reading, you need a processor board running the GPS tutorial. Just make sure you set the switches on JP1 to suit the processor used.

The first fix can take a few minutes, depending on your location. Put the board outside, or on a window seal. Inside fix are harder to get.

JP2 is used to ouput a 1 pulse per second from the receiver to pin 0 of the interface bus. It can be used to generate an interrupt every second.

Files and links: