# $Id: realtime-design,v 1.6 2001/11/03 03:15:49 tramm Exp $

The onboard real-time system has several responsibilities:

- Servo ouputs (PWM)
- Gyro inputs (PWM)
- Gyro inputs (analog)
- Altimeter
- Compass
- Engine monitoring
	- Fuel (analog)
	- N1 engine rpm (pulse counting)
	- N2 rotor rpm (pulse counting)
	- CHT (analog)
	- EGT (analog)
	- Battery level (analog)
- Relays
- Servo control input (RS-232)
- Status output (RS-232)
- NMEA input from GPS (RS-232)


The PCB should have the following ports:

- System power/ground
- Servo power/ground pins
- 8 Servo output ports (with power and ground)
- 4 Servo/Gyro input ports
	- Roll?
	- Pitch?
	- Yaw?
	- Unused
- 8 analog input ports
	- Fuel
	- Gyro pitch
	- Gyro roll
	- CHT
	- EGT
	- Battery
	- Sonar altimeter
	- Flux-gate compass
- 4 Pulse counting inputs
	- N1
	- N2
	- Sonar altimeter
	- Unused
- 4 LED outputs
- 4 Relay outputs
	- All for payload
- 1 or 2 RS-232
- In-system programming port


The real-time board can receive power from the same battery as the servos,
or use its own supply.  The servo power is likely to be unclean and require
filtering, so some caps should be onboard to do that.

The gyros (of both kinds) are going to be mounted externally and connected
via a cable, so there is no need to make space on the board for them.
The MicroGyro 100 does have a very simple mounting system, and the final
product should probably have

Right now we're using the Mega103, which is no longer available.  The
new chip is the Mega128.  It has an extra UART and can run at 16 MHz.
Since availability of the 103 is nil, we need to transition to the 128
chip design.  More details on it:

	http://www.avrfreaks.net/Devices/devices.php?action=1&devid=54

However, the Mega128 series are only available in SMD packaging.  The
smaller chips are more suited for development.  The Mega16 has a few
less ports, but appears to be fully functional:

	http://www.avrfreaks.net/Devices/devices.php?action=1&devid=56


