Project: your own template

This year you have written dozens of two-point controllers: a heater here, cooling there, almost the same code every time. This week you build the template you will copy from now on. A good template has three parts: a settings block holding everything you need to adjust, logic you never have to touch again, and documentation that says how to use it.

The idea#

A subroutine regeln handles one control loop. What it needs, it gets in registers:

When heating, “too cold” switches on and “too warm” off, when cooling it is exactly the other way round. For that the subroutine swaps the roles of ein and aus with two select – after that the actual hysteresis is the same line for both directions.

The state lives in the device#

Every control loop needs its own memory: was the device on? Instead of spending registers or the stack on it, the subroutine simply reads the state back from the device:

lbn on typ name On Average      # the state lives in the device itself
snan tmp on
select on tmp 0 on

That way every further loop costs only six lines in the main part, and the subroutine stays unchanged.

Safe state per direction#

If a loop's sensor is missing, a heater switches off and a cooler on. The display “Regler” shows how many loops are currently running without a sensor.

The setup#

Milestones#

1. The living room heats with hysteresis (19/21 °C).
2. The cold room cools with hysteresis (6/2 °C).
3. Sensor failure: heater off, cooler on, the display counts the failed loops.
4. The loops are independent: if one fails, the other keeps controlling.