Due to recent theories put forward as explanation for anomalous behavior of the cortex I decided it was time to dig into the power distribution scheme used within the cortex controller. The result of this initial investigation is this high level overview block diagram.
A summary is as follows.
- Main battery power is sent via the two 4A PTC devices to the motor ports.
- A 1A 5V linear regulator is used to supply power for the digital and analog sensors.
- A 2.5A 5V switching regulator is used to supply power for the two micro-controllers via a 3.3V regulator (probably a MCP1700, 250mA LDO, it’s hard to tell exactly) as well as supply power for the USB peripherals, uart and I2C ports. Input to this regulator is either the main battery or backup battery depending on competition mode and voltage of the main battery.
The status LEDs on the cortex are used to display the battery status as follows.
Non-competition mode.
Main battery
6.5V___________ ROBOT led is green
< 6.5V and >5.5V__ ROBOT led is yellow
< 5.5V___________ ROBOT led is red
Competition mode
In competition mode the cortex will switch between main and backup battery if it is connected. The switchover occurs at 6.2V as main battery voltage drops and switches back when main battery rises over 6.9V. Main battery monitoring also happens but instead of causing a solid led indication the led will flash.
Led indications on the cortex are at best confusing due to the many different things they try to convey. In an attempt to document this I have started to put together some animated gifs that simulate the displays. The following shows standard competition status when using VEXnet.
Competition / Disabled / Single joystick / Good main battery / Good backup battery
Competition / Disabled / Single joystick / Low main battery / Good backup battery
(robot flashes yellow)
Competition / Disabled / Single joystick / discharged (or disconnected) main battery / Good backup battery
(robot flashes red)
Competition / Disabled / Single joystick / Bad backup battery
(robot flashes fast red, main battery status can not be displayed)