Automate and monitor the physical systems in your home

Programmable Devices

A programmable device has a single, user-programmable output function. These are commonly used in the home automation system when you need to create an "on" or "off" value from a combination of other signals. The function allows an arbitrary number of inputs and supports and AND, OR, XOR, equality, inequality, and NOT operations. The house_water_valve function is defined as shown in Listing 1.

Listing 1

house_water_valve Function

01 (house_preset == "summer_away"          # equality test
02     || house_preset == "winter_away"    # OR and equality
03     || house_water_valve == "closed"
04     || alarm_leak)
05 && house_water_valve != "open"          # AND and inequality

Programmable devices are built by running the Programmable script in the Combinational Logic scripts area. To build the house_water_valve device, we gave it the script parameters shown in Table 3. In this way, we built a device with name house_water_valve with an output called house_water_valve_closed. The function itself lives in a file called house_water_valve.logic.

Table 3

Water Valve Script Parameters

Parameter

Value

file_name

"Scripts/user/house_water_valve.logic"

id

"house_water_valve"

logic_function

""

output

"house_water_valve_closed"

State Machines

State machines are general-purpose, user-programmable devices. We won't cover all the details for building state machines (you can find documentation online [9]), but we will demonstrate an important state machine component – the table – that defines the state machine functionality.

The state machine table in Listing 2 defines four-way switch behavior. The four-way switch uses two solid state relays, each with its own on/off signal (pole1 and pole2).

Listing 2

Four-Way Switch Behavior

01 "four_way_switch":
02
03 # turn on conditions
04 -
05   When: {switch: "on", reset: "off"}
06   State: {pole1: "on", pole2: "off", light_sense: "off", switch: "on", reset: "off"}
07   Then: {pole1: "off", pole2: "on"}
08 -
09   When: {switch: "on", reset: "off"}
10   State: {pole1: "off", pole2: "on", light_sense: "off", switch: "on", reset: "off"}
11   Then: {pole1: "on", pole2: "off"}
12
13 # turn off conditions
14 -
15   When: {switch: "off", reset: "off"}
16   State: {pole1: "on", pole2: "off", light_sense: "on", switch: "off", reset: "off"}
17   Then: {pole1: "off", pole2: "on"}
18 -
19   When: {switch: "off", reset: "off"}
20   State: {pole1: "off", pole2: "on", light_sense: "on", switch: "off", reset: "off"}
21   Then: {pole1: "on", pole2: "off"}
22 -
23 # init state
24   When: {reset: "on"}
25   Then: {pole1: "on", pole2: "off"}

Each time the state machine sees a switch for an "on" or "off" event, it checks the state of its light_sense input (a current sensor) and decides whether or not to toggle the solid state relays. The reset condition puts the relay signals back into a known state.

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