Smart Refrigerator Magnet

Smart Refrigerator Magnet

This project started when I had an issue with my Hotpoint Refrigerator. We had a lot of trouble maintaining a cold temperature. So I did some research online on how to fix this issue. I found that the refrigerator controller has a communication port. So I did some more research and was not able to find anything on the communication protocol specific to this refrigerator. My refrigerator is about 15 years old.

To make this story short, I was challenged to reverse engineer the communication protocol. The hardware layer use a UART @9600bps, 8 bit, one stop bit, no parity. Now with the protocol, I would be able to use the Hexiwear to communicate with my refrigerator to extract the Fresh Food and Freezer temperature.

Hardware Interface

Electrically, the interface uses a 0V to 5V signal. The signal is inverted in respect to the UART interface. Also this is a single wire communication, therefore the Transmit and Receive signal are on the same wire.

Software

The Software was developed using the NXP Kinetis Design Studio (KDS). The Smart Refrigerator Magnet software was added to the Hexiwear Firmware found on GitHub @ https://github.com/mikroe/HEXIWEAR.

Some feature of FreeRTOS where used to accomplish this project.

The communication interface used is UART2. The interface is configured @ 9600bps, 8 bit, 1 stop bit, no parity.

The interface is also configured to generate interrupt on the reception and completion of transmission of 8 bit of data. After the packet is received from the refrigerator, a SemPost is issued to trigger an update of the Temperature display update task.

The Hexiwear act as a master initiating a request by sending a packet to the refrigerator. Then the refrigerator respond with a packet containing the Fresh Food and Freezer temperatures. The temperatures are both of 16 bit values. The values are then converted to Fahrenheit by dividing the received value by 100.

Future Development and Improvements

• Use the Queue feature of the real-time OS to manage the communications

• Not all features where implemented, more Command Requests to the Refrigerator are available, for instance: Diagnotics test, Damper Test, Fan Test, Defrost Test

• Add Bluetooth communication to allow remote access

• Add Temperature Monitoring (Alarms)

Supported Refrigerators

This project was tested using a Hotpoint Model: HSS25IFMBWW.

GE and Sears should work see Model Series below:

• GSS20

• GSS22

• GSS25

• ESS22

• ESS25

• HSS22

• HSS25

• SSS25