Controlled Temperature Home with Safety Features.
Description of Operation:
In this project, a small home automation system will be discussed and implemented. This section gives the reader about the general behavior of the system. A complete view of the operating environment is shown below. Please refer to this image when reading about the behavior of the system.
When the user enters the corridor, the system activates and turns ON the corridor lights and ventilation motor. The system may also turn ON the AC unit or Heater unit depending on outside temperature. Additionally, two safety features, which did not require user’s presence, are also supported by system. These safety features include Fire alarm circuit and Sump-pump unit.
The ‘Master Start/Stop’ control allows user to enable/disable the entire automated process of controlling ‘Ventilation Motor’, ‘Corridor Lights’, ‘AC Unit’ and ‘Heater Unit’.
When enabled, the system continuously checks for user’s presence in corridor lobby. When the user enters the corridor upon arrival, ‘Proximity Sensor’ installed in the corridor detects the user and the system turns ON the ‘Ventilation Fan ’ and ‘Corridor Lights’ installed in corridor. The system then enables two temperature sensors installed outside the building and gets the temperature reading. If outside temperature is greater than 30° Celsius, the system starts ‘AC unit’. If outside temperature is lower than 0° Celsius, the system starts ‘Heater Unit’. If the temperature is between 0° Celsius and 30° Celsius, the system does nothing.
When user enters the house, the ‘Proximity Sensor’ installed in corridor lobby detects it and informs the system. After 1 minute, the system turns OFF the ‘Ventilation Motor’ and ‘Corridor Lights’ if the system does not detect user’s presence in lobby for this duration.
The ‘AC unit’ and ‘Heater unit’ are interlocked to ensure efficient usage of energy. The system controls the ‘AC unit’ by receiving temperature reading from ‘Temperature Sensor One’. Similarly, the reading provided by ‘Temperature Sensor Two’ is used by the system to control the ‘Heater unit’.
‘AC unit’ contains three internal motors: ‘Condenser’, ‘Compressor’ and ‘Evaporator’. It also provides three indication lights to indicate status of each motor. To make sure that ‘Compressor Motor’ does not energize when system is subjected to extremely high or abnormally low pressure, the AC unit internally equips ‘High Pressure Sensor’ and ‘Low Pressure Sensor’. This is additional safety feature for ‘Compressor Motor’ to protect its coil from burning. The three motor ‘Overload Relay’ are connected in series to ensure that if any one motor in the AC unit fails, the whole unit shuts down.
The Heater unit is activated if ‘Temperature Sensor Two’ reads temperature below 0° Celsius. It consists of Heater motor (Heater coil) and Heat ON/OFF indication light.
The system constantly checks for Fire by sensing the presence of smoke inside the house. The ‘Smoke Detector Sensor’ triggers ‘Fire indicator’ circuit, which activates a high frequency ‘Buzzer’ and ‘Fire indicator light’. The circuit is designated such that user is not allowed to turn-off the Buzzer for first 10 seconds after the warning signal was triggered. After 10 seconds, the user may push ‘Buzzer Stop’ button to stop buzzer, however, the fire indicator light will only turn OFF when there is no smoke present inside the house.
The system also controls the ‘Sump pump’, which is installed in the basement. The system turns ON the pump when ‘High Water Level Limit Switch’ is activated (closed). The pump continues to run until the ‘Low Water Level Limit Switch’ opens. The Status of Sump pump is indicated by an indicator light.
When the Master Start/Stop control is used to ‘Stop’ the automated process, the safety features are not disable and continue to monitor house environment.
The bits and Bytes of the system
Here is the ‘program’ that would do the job. This program is the actual program which would be compiled by a specialized compiler tool-chain for appropriate Programmable Logic Control. If you want to hack into a Industrial system and control doors and motors from your home, it is probably a good idea to get yourself familiarize with ‘reading’ this type of ‘programming language’. It is technically called Relay Ladder Diagram.
Control Variables
Here is this list of all the ‘variables’ that this program uses. All the symbols are associated with one of these variable. I’ve tried to make it less confusing, but know that the symbols that have obscure names are actually dummy variable — much like a intermediate variable that computer programming language compilers generates when compiling.
Ending notes
This blog described how modern automation systems are actually developed and what are the key components of a program that describes a automated process. If an Ethernet card is connected with the main controller (Programmable Logic Controller), it is possible to control the process through internet. This is where things can get out of control if no proper security measures are taken. A knowledgeable hacker can easily control the Fire safety of the house even if the safety system is not even controlled by master switch.
Therefore, it is important to note that the system that needs to operate all the time must be electrically isolated from other systems, since a common control plane has a chance of getting exploited by the attacker at any time.
