PSAS/ news/ 2002-03-03

Designin' dem PIC boards

Participants: Tim and Andrew. Waaaaah.

What we did: First pass design on the "processor section" of the CAN nodes. We're breaking the CAN boards up into four different independent schematics:

CAN Module Section Diagram.jpg

    1. PIC and 5V switched power supply
    2. Application area (node dependent)
    3. Standard Mechanical (for screw or card cage mounting)
    4. Interface connectors (CAN and power connectors)

We'll use EAGLE ( to design the sections, from schematic to full on layout, and then use our vaporware Gerber editor to paste them all together to get actual "whole" boards.

Processor Section:

Here's what we came up with for the processor section. Basically, it includes the power supply, CAN transcever, ICD interface, a voltage reference (optional to stuff), main oscillator, secondary oscillator (optional to stuff) and frankly that's it. We take more of the signals and pins and route them towards the application board (where the application circuitry can get access to the signals it needs).

PIC section schematic.jpg

Power Supply for PIC boards:

Voltage For what?
12V applications only - can take it off bus (usually for power anyway). Be carefull of shorting bus!
5V Switching regulator; main supply.
3.3V for digital chips - low current supply. Use LDO linear.

BS'ed power consumption:

Node Power needed
GPS 5V @ 200mA; power amp 5V @ 50mA = 250mA
IMU 12V @ 40mA
PYR ? 100mA to charge batteries? Radio = 12v @ ? Ma
ATV 100mA to run BOB-II board?
SBS ?? Should be off 12V supply and shore power.
MAG ?? probably < 100mA

Power Supply filter:


Things to remember:

Task List: