PCB 2.0 General Overview
The revision 2.0 PCB is divided into two physical
boards. The first board represents pages
1 - 8 of the schematics. These pages
represent the main board which contains the microcontroller(uC), memory,
etc. The second board is the analog and
sensor board referred to as the daughter board.
This board contains the gyros, accelerometers, etc.
The two boards interface over an I2C bus.
The following is a more detailed description
of each page of the schematic.
You can download the PDF from:
GPS - Page 1
This page contains
the uBlox TIM GPS unit. It communicates
via a 3V UART to our microcontroller on UART1, the second UART on the
AT91. There's a boot header jumper
provided to force the component to boot into Debug mode by tying to 3.3V, or to
boot to normal operating mode by connecting to ground.
This page also shows a 3 pin header for an
external DGPS input to the TIM module.
The reset for the GPS unit is connected to the uC reset.
Headers - Page 2
This page shows the main
board system headers. The 20 pin
connector isn't used in the current design, but may be used for future daughter
cards. Two three pin headers are the
interfaces to the N1 and N2 hall effect sensors measuring rotor RPM.
The 8 pin header is the connector for the
JTAG - Page 3
Here we have the
20-pin standard ARM JTAG connector. The
JTAG is used for programming the system flash.
The header can connect to the Macraigor Wiggler:
We may be able to
program the flash through UART0 in which case this header will be unnecessary.
This page also shows
the watchdog overflow output being used to drive a system reset.
We also have a single push-button reset as
Main - Page 4
The uC page.
This page shows the signal aliases used for
the PIO, UART, I2C, etc. in the design and the pull-ups on the data bus.
Memory - Page 5
The system is
designed with a 2MByte flash memory and a 512KByte EEPROM.
The EEPROM is intended for data logging and
storing any sensor calibration or other persistent data.
The Flash memory is divided into two boot sections
which can be selected by setting the J7 header.
One position boots to the lower 1MB partition containing a boot loader
most likely an Angel debugger in our final design.
The upper partition will contain our
application code and will be the non-debug boot.
This design follows the Atmel evaluation
board so you can read more about this configuration in their docs:
Power - Page 6
This page contains
the lithium battery charger, the 3.3V and 1.8V supplies, and the decoupling
capacitors for the AT91. We may in the
future add an input from an alternator-like device to charge the lithium
cell. Once the power requirements
analysis is completed we will know if we're using a coin cell or a multiple
cell lithium battery.
- Page 7
We've added a
MAX3221E 250kbps RS-232 converter to communicate with a PC serial port.
Servo Controller - Page 8
Here we are driving
8 servos via Digital outputs from the AT91.
We feed them into two IL715 optoisolators that level convert from our
3.3V logic to 5V logic on the output.
This page also includes the 12-pin servo header.
Accelerometers - Page 9
This page contains the ACH-04-08-05 3-axis accelerometer
manufactured by Measurement Specialists.
The schematic was taken from a TI application note:
The analog signals
are amplified and filtered by a TLV2774 quad op-amp and fed as analog input to
the AD7417 ADC. This ADC is capable of
100ksps operation and interfaces to the microcontroller via an I2C bus.
The ADC has a 5-way mux to select any of the
four input sources or a fifth internal temperature sensor.
In addition, the ADC has an over-temperature
warning output that we will monitor.Up
to eight of the AD7417's can be placed on the I2C bus.We're using two in our design.
Daughter Headers: Page 10
The daughter board
has two headers.The first header is the
8 pin main board connector.The second
is a 4 pin header containing ground, AEXT1, and AEXT2.AEXT1 and AEXT2 are two extra analog inputs from
the unused inputs on our ADC 7417's.This
4 pin header is a screw-down block on the board.
Gyros: Page 11
We're using three
ENC-03J gyros from Murata.Each gyro
measures a single axis and is amplified and filtered before being fed to our
second AD7417 ADC.Currently the component
values are not complete.
Thermocouples - Page 12
TBD: This page may
be removed if not needed.
Bill of Materials
This list is a summarized BOM containing estimated
pricing.In some cases I've found
pricing in single unit quantities from vendors.
Where possible I've used this pricing below.A more accurate pricing quote will be
complete one we complete the board layout and submit it to an assembly house.
|BATTERY HOLDER- Keystone
PCB Flyer - a really