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:

http://autopilot.sourceforge.net/rev2.pdf

Main Board

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.

http://www.u-blox.com/products/tim.html

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 daughter board.

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:

http://www.ocdemon.net/Merchant2/merchant.mv?Screen=PROD&Store_Code=MTS&Product_Code=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 well.

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:

http://www.atmel.com/atmel/acrobat/doc2635.pdf

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.

COM Port - 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.

Daughter Board

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:

http://www-search.ti.com/search97cgi/s97_cgi?Action=FilterSearch&Filter=TI.filter.hts&Site=new&keywds=ach-04-08-05

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.

Part	Cost	Quantity
BATTERY HOLDER- Keystone 1062	1.15	1
Capacitors	3	?
D-BAS32L/1N4448W	0.44	?
Headers	12	?
Resistors	4	?
Switch	0.47	1
AT91R40008*	18.00	1
AT24C512*	10.00	?
AT49BV1604A*	10.00	?
MAX3221E	2.00	1
74LV74	0.60	?
MAX1793-3.3V	2.00	1
MAX1793-1.8V	2.00	2
MAX6386-D1	1.50	?
MAX1736	2.00	?
SI4431DY	0.62	?
ENC-03J	30.00	3
AD7417	7.78	2
LMV324	0.81	?
ACH-04-08-05*	50	1
TLV2774	2.25	?
TLV431	0.75	?
TIM	70.00	1
CMX-309HB	3.00	?
PCB*	20	2
Assembly	???	???

Total		242.15