Start a sequence from a schematic

Add a schematic button that starts an Arc sequence, and show the active stage.

An operator starts a sequence with a button on a schematic. The button writes 1 to a channel, and the sequence starts when the channel gets the value. A state indicator on the same schematic shows which stage runs.

Before you start, you need:

• An Arc automation with a sequence, such as the one in write a test sequence.
• A schematic with the valves that the sequence controls. See control hardware from a schematic.

Create the channels

Create two channels:

• start_cmd -> A virtual uint8 channel. The button writes to it. Only the live value matters, so Synnax does not need to store it.
• press_stage -> A uint8 channel with an index. The sequence writes a number for each stage to it. Because Synnax stores it, the schematic shows the last stage when you open it.

Add a start button

1. Turn on editing for the schematic, and add a Button symbol.
2. In the Style tab of the symbol, set Label to Start.
3. In the Control tab, under Command, set Channel to start_cmd. Leave Mode at Fire, which writes 1 each time you click.

Start the sequence and write the stage

1. Open the Arc automation, and change the code so that each stage writes its number to press_stage, and start_cmd starts the sequence:

   import time
   
   sequence press {
       stage pressurize {
           1 -> press_stage
           1 -> press_vlv_cmd
           tank_pt > 300 => next
       }
       2 -> press_stage
       0 -> press_vlv_cmd
       time.wait{duration=10s}
       stage vent {
           3 -> press_stage
           1 -> vent_vlv_cmd
           tank_pt < 5 => next
       }
       0 -> vent_vlv_cmd
       0 -> press_stage
   }
   
   start_cmd == 1 => press

2. Click Start in the controls bar. If the automation already runs, click Redeploy.

start_cmd == 1 => press starts the sequence on each new 1. A click while the sequence runs does nothing. After the last step, the sequence stops, and the next click starts it again. See the execution model.

If your sequence has an abort stage, write a number for it too, such as 4 -> press_stage.

Show the stage on the schematic

1. Add a State indicator symbol to the schematic.

2. In the Telemetry tab, under State, set Channel to press_stage. Under Staleness, set Timeout to a value longer than your longest stage, such as 60 seconds. The indicator changes the color of its label when no new value arrives for that time.

3. In the Options tab, add an option for each stage, with a name and a value:

   Name	Value
   Idle	0
   Pressurizing	1
   Holding	2
   Venting	3

The indicator shows the name of the option whose value equals the channel value. It shows Unknown for a value with no option.

Start the test

Turn off editing, then click Start on the schematic. The schematic takes control, then writes to start_cmd. The indicator shows Pressurizing, and the press valve opens.

The schematic writes at authority 1 by default, and the automation at 255, so the automation keeps control of the valves. If you give the automation a lower authority than the schematic, a click on the button also takes control of the valves. The indicator then shows Pressurizing, but Synnax drops the commands from the sequence, and the valves do not move. See control authority.

To add an abort button, repeat these steps with an abort_cmd channel. See write a test sequence.