pico_statemachine_dimmer

Test of setting up the Pi Pico's PIO state machines to drive LED light dimmers

Light state

Each light has an associated instance of the LightState class There is an array of 8 LightState instances, one per PIO state machine.

LightState records:

The current dimmer level.
If we are currently dimming or brightening
Remembers the ON/OFF state from the last use of the switch, for next time the switch is used

Switch Down Events

Events are recorded by setting bits in an Integer in each LightState record. The interrupt handler sets events. The main loop handles and clears events. There is currently no locking of the event Integer, so it is possible to lose a DIMM event. ON/OFF events are one off events, so shouldn't be lost.

ON: The light is turned ON, if it was OFF
DIMM: The light alternately dims or brightens, if the switch is held down for longer than 1/2s
OFF: The light is turned OFF, if it was ON, and the switch was down less than 1/2s

The PIO state machines

Each state machine monitors an input switch pin.

On switch down (earthed), the state machine sends an interrupt
If the switch stays down, an interrupt is sent every 1/16th of a second
On switch up, the state machine sends a final interrupt

The interrupt handler

Timing is done by incrementing a per state machine counter, for each interrupt that is sent by a state machine. Interrupts will occur approximately every 1/16s, while the switch is down, so 8 interrupts represent 1/2s.

If the light was off, the output light pin is turned on, after 2 interrupts (1/8th second)
- An ON event is set, for the main loop to handle
- the light pin is set to on
If the switch is held down for more than 8 interrupts (1/2s)
- A DIMM event is set, for the main loop to handle
If the switch is released within 8 interrupts (1/2s)
- If the light was ON when the switch was pushed,
  - an OFF event is set, for the main loop to handle
  - The light pin is set to off
- The interrupt timing counter is reset to 0
- The final ON/OFF state is recorded in the LightState
If we were Dimming
- reverse the dim direction
- The interrupt timing counter is reset to 0
- The final ON/OFF state is recorded in the LightState

The main loop

Each light's LightState is checked at approximately 1/100th of a second intervals, for ON, OFF or DIMM events set by the interrupt handler.