Finite State Machine
The program will be controlled through the use of a Finite State Machine to ensure that inputs can only be serviced at the appropriate periods. The states defined are defined as follows:
| State | Description |
|---|---|
Off | The vehicle is not receiving power |
Idle | The car is on, but no pedals are pressed |
Driving | The gas pedal is pressed car is in motion. |
| Brake | The brakes are engaged and the car is not moving |
Each input can only be serviced during certain states. Certain inputs can also cause transitions when serviced during certain states.
| Input Device | Off | Idle | Driving | Braking | Notes |
|---|---|---|---|---|---|
| Horn |
|
|
| ||
| Power Switch |
|
| Transitions between the "off" state to the "idle" state | ||
| Emergency Switch |
|
|
| Driver needs to be able to always access this | |
Push-to-talk |
|
|
| ||
| Direction Selector |
| Need to be holding the brakes to change gears | |||
| Headlights |
|
|
| ||
| Turn Signals |
|
|
| Direction indicator lights must flash at a rate of 90±30 flashes per minute (between 1 and 2 Hz) | |
| Hazard Lights |
|
|
| ||
| Cruise Control ON/OFF |
|
| Needs to turn off automatically once the program transitions to "idle" | ||
| Cruise Control Inc/Dec |
| ||||
| Regen Strength |
|
|
| ||
| Gas Pedal |
|
| Triggers a transition from the "idle" state to the "driving" state when pressed, and a transition from "driving" to "idle" when released | ||
| Brake Pedal |
|
|
| If anti-lock brakes are used, the front wheels must be stopped before the back wheels |
ADC Driver
On the STM32 is a 12-bit analog-to-digital converter (ADC). The role of an ADC is to take an analog signal as an input and give as output a digital number proportional to the magnitude of the input signal. The following formula can be used to determine the ADC reading:
The ADC has 19 multiplexed channels, with 16 of them being mapped to analog input pins. The 16 external pin mappings for the STM32 are as follows:
| ADC Channel | Pin Name |
|---|---|
| ADC_IN0 | PA0 |
| ADC_IN1 | PA1 |
| ADC_IN2 | PA2 |
| ADC_IN3 | PA3 |
| ADC_IN4 | PA4 |
| ADC_IN5 | PA5 |
| ADC_IN6 | PA6 |
| ADC_IN7 | PA7 |
| ADC_IN8 | PB0 |
| ADC_IN9 | PB1 |
| ADC_IN10 | PC0 |
| ADC_IN11 | PC1 |
| ADC_IN12 | PC2 |
| ADC_IN13 | PC3 |
| ADC_IN14 | PC4 |
| ADC_IN15 | PC5 |
In addition, the ADC has two different modes for converting analog signals:
Single Conversion Mode: The ADC performs the conversion for a channel and stops after the conversion for that channel has been completed
Continuous Conversion Mode: The ADC will convert a channel indefinitely at regular intervals