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PCB Design Review
PCB Design Verification

Last modified 28 March 08

GENERAL

Key components

Epson Gyro. Bought from Far East Noble Sdn Bhd 

 
XV-8100

GPS receiver with DR (dead reckoning)

Trimble Lassen DR+GPS

short form, manual and specification

App note 1

App note 2

Dev kit schematics 

PCB

Ordered at www.cogra.se. 

Schematics

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Component placement 
(75mm x 102.4mm)

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BOM (Bill of Materials)

2 main functionalities, Powercontrol (PC) IBus or not, and GPS. Combinations are:

p&p not included. 25% ax included.

Bill of materials with ordering info including prices

Design decisions

For "Tacho" and "direction" I have put in 0ohm resistors so that the 8051 can control the Lassen module directly, or use external signals filtered in the op-amps.

Ignition can also be detected from IBus. In that case the Ignition input can be used as general input.

Voltages onboard are
- filtered 12V
- VCC 5V from TH3122. Will power 3V3 UPS.
- 3V3 UPS. Will always be there. Well, not if battery voltage goes below 10.1V +- 0,25V. (Comes back at 10.5 +-0,25V) Will supply 8051 that is always on. Will support GPS with backup voltage.
- USB 5V. Will source 3V0 for gyro and the external GPS antenna amplifier. Presence will also enable the 3V3 regulator that is powered from 12V.
- 3V3 powers GPS, op-amps and USB chip.

The GPS has input for battery backup. This is not used as it will take 30s or so to boot PC anyway. Maybe 3V3_UPS can be used...

Power regulator sources are selected so that cpu and melexis and IO can be excluded to get a pure GPS module. Now, if "battery" backup is wanted on the GPS, both regulators has to be put in place. I think that is worth while not having to change batteries.

Power consumptions

FT232 15mA
Melexis IBus 100uA
8051 0,5mA
GPS 190mA
active antenna 30-50mA
Gyro 1,7mA
TP2975 180uA, 1uA in shutdown

I think the sleep mode board will draw less than 1mA, and in shutdown (<10V) maybe 30uA. Should be ok.