Although five-day weeks are a boon to white- and blue-collar workers, some businesses need to be extra careful during the two days of the weekend. For example, commercial monitoring systems generally protect warehouses with large freezers and cooler rooms. However, between Friday evening and Monday morning when the food shelf remains closed, a unit may blow a fuse. Usually, this goes unmonitored with the result that food is found ruined by Monday. The inexpensive, tiny credit card sized single board computer, the Raspberry Pi or RBPi was found to be a suitable base for a temperature monitor and alarm for a walk-in display-case cooler and freezer.
The project objectives are very simple. A low cost temperature monitoring system is required that can send free text messages when the temperature within the freezer or fridge goes outside the acceptable range.
For this, the RBPi has to monitor the temperatures within the fridge unit and the freezer. For the fridge unit, the valid temperature given is 33F, while it is -10F for the freezer unit. However, since stocking personnel and customers open the doors frequently during the business hours, temperatures in the fridge rises to 60F. Therefore, a wider temperature range is to be allowed during business hours as compared with the temperature range during off hours.
To draw the attention of maintenance personnel, the RBPi has to provide an audible temperature range alarm, which makes a noise when the temperature goes beyond the range. Additionally, a switch button is necessary, as a snooze, to silence the noise when the problem is receiving attention. As personnel are expected to be away on weekends, the RBPi is required to send a text message to someone who would be able to either fix the problem or move the food to a safer location. To make the temperature visible to the staff, an LCD temperature display is used. The RBPi is required to project the current temperature on a wall mountable LCD mounted outside the fridge/freezer unit.
Parts needed for the project include the RBPi Model B, although Model A can also be used. However, since Model A has only one USB port, an additional USB hub will be necessary. For the operating system, you will need the 8GB SD card with the NOOBS installer image. The Adafruit RGB 16×2 LCD kit with Keypad is the most suitable, since it has five momentary push-button switches useful for navigation. For connecting to the internet, you may use the Wi-Pi Wireless Adapter. In case you are planning for an XBMC solution, you will also need an Ethernet cable, an HDMI cable and wireless keyboard/mousepad.
For the audible alarm, you will need 2×3.5mm stereo headphone plugs, a portable speaker and audio cable. To house the RBPi, a suitable case will also have to be used.
You can use 2x DS18B20 Digital temperature sensors for monitoring the two temperatures. Although the stand-alone IC components are just as good, prepackaged waterproof units are available; these will suit the project better. When you are ready with the parts, follow the instructions in this tutorial to set up the project and to calibrate it.
