Adding Resources to the Concept Car
The Concept Car has a modular architecture allowing the addition of resources in a simple way. In order to integrate a new element in the Car architecture it is necessary to integrate it to a new AT90CAN128 board. The AT90CAN128 boards are the interface between the sensors and actuators (i.e. the environment) and the Concept Car's CAN bus. Their main purpose is to do low level tasks, like PWM de- and encoding.
The characteristics of the AT90CAN128 boards are presented in the following.
All boards featuring an AT90CAN128 microcontroller are supposed to fit into any of the 8 spaces at the CAN bus box. Therefore they share the same dimensions, drill holes for mounting and SUB-D jack position. They all have the same dimensions to be interchangeable in place.
This dimensions are precisely the same used for the SensorBoards in the old Hardware Revision 1.0, all Revisions >= 1.2 must comply with these dimensions.
Since the boards can be stacked, it is a good idea to place all connectors, switches and LEDs near the borders.
Figure 4.1 presents the board dimensions.
First apply this in the schematic:
- Add the 4 drill holes as parts MOUNT-HOLE3.0
- The SUB-D CAN connector must be of type F09H
To get a proper board, follow these steps in eagle (when starting from scratch):
- Set the grid to 1mm
- Move the edges of the dimension polygon so that it's a square of 73mm x 73mm, with its origin being in the bottom left edge.
- Move the drill holes to the positions 4mm apart from each edge
- Rotate the SUB-D CAN connector to face upwards and move it to position 37.506mm/60.88mm. MOVE CAN_BUS (37.506mm 60.88mm) would do this.
These are recommendations on what operational controls to use to supply a uniform look&feel (and in some aspects programming) of the sensor- and actor-boards. The placement is not critical, it just looks better this way.
- The CAN bus driver is designed to signal the bus state with 2 LEDs (a green one for error active state and a red one for bus off state). Those LEDs are attached to I/O-Pins PA7 (red LED) and PA6 (green LED), over a resistor of 220 Ohms to ground each. The LEDs (package: CHIP-LED0805) should be placed as follows:
- suggested position for green LED: 1250x200mil, parallel to side
- suggested position for red LED: 1075x200mil, parallel to side
- A green power on LED (CHIP-LED0805) that is directly attached to the power supply is recommended. It should be placed at 850x200mil, parallel to side (next to the CAN LEDs), with a resistor of 220 Ohms.
- The reset switch (10-XX) should be placed near the boarder at 550x275mil.
- The ISP and JTAG adapters (both ML10L) should be placed at 2450x800mil (JTAG) and 2450x1610mil (ISP). ISP is mandatory, but JTAG can be omitted.
- If any additional LEDs are required, they should be placed at the lower border, like the CAN LEDs 200mil away from it.
- Connectors to peripherals or other boards must be low enough to avoid trouble with other boards in the stack. Recommended type is for example L02P, L03P, L05P.