Finis is a demonstration of a discrete Moore finite state machine running on a AVR microcontroller.
For this demonstration I am using a simple layout with an ATmega328P microcontroller some LEDs, NPN Transistors and a Photoresistor. The ATmega uses an external Crystal with 16 MHz clock rate. Our application shows the brightness detected by the photoresistor with different colored LEDs. We need four of them (red, green, yellow, blue). I use NPN transistors to drive the LEDs. The following schematic should help you to rebuild my layout.
I have written a Table-Driven State Machine in C. This State Machine has 3 main states and 3 transitional states. The input is derived from the value read by the ADC. Connected to the ADC is a photoresistor. The ambient light conditions are divided in three ranges.
Here is the state machine definition table
| State | Input Bright | Input Dim | Input Dark |
|---|---|---|---|
| GREEN | GREEN | TO_RED | TO_YELLOW |
| RED | TO_GREEN | RED | TO_YELLOW |
| YELLOW | TO_GREEN | TO_RED | YELLOW |
| TO_GREEN | GREEN | GREEN | GREEN |
| TO_RED | RED | RED | RED |
| TO_YELLOW | YELLOW | YELLOW | YELLOW |
The neat thing about using a table is this can be translated directly into code.
Have a look at the struct s_type and the global arrays FSM in finis.c
This implementation currently uses _delay_ms() to control the FSM tick frequency.
Depending on what your application does it might be better to use a Timer register.
finis state machine example for 8bit avr
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