• Schematic

    RMcMillin • 04/28/2019 at 11:36 • 0 comments

    I've added a very rough schematic to get started.  Before I commit to the temperature sense and light sense circuit I will purchase a few parts to test them out.

    I've also added a system specification and function description document to explain how the system works. It's mostly for me to remember why I chose certain resistor values and components.

    These files will be regularly updated as I make changes  - they're very rough.

  • Basic functionality and part selection

    RMcMillin • 04/27/2019 at 17:31 • 0 comments

    I came up with a simple hardware block diagram and chose a few parts that will make up the main system components.  I think I should remove low cost from the title because I don't think it will be as inexpensive as I was hoping.

    I thought about various configurations that the system could be in and decided that I wanted to put everything in a single package.  This may cause issues in the future as batteries do not run well in cold and I'm not sure how well wifi will penetrate the walls of a fridge.  I will try to put everything in a single package for easy installation and if there are issues then I will try to work around it or change the design.

    I've attached a basic hardware block diagram and I would like the system to following way:

    • Achieve lowest power possible by turning things off or entering sleep modes
    • Wake up periodically to test temperature and battery voltage and store data to memory.  If there is a temperature issue then wake up on a higher frequency period.
    • When the door opens, I want the system to wake up and display the current temperature
    • Access to data through a phone app
    • phone app to change alarm thresholds for temperature and battery discharge level

    I chose to use an RTD over a cheaper type of temperature sensor to have some decent accuracy since this is for food safety.

    I have decided to use the ATwinc1500 wifi module over ESP8266 and its derivatives due to a lower current consumption in idle mode.

    I will probably use the ATmega328pb MCU since I already have libraries made and I am comfortable with it.  For a final product the MCU should probably be optimized for what the system actually needs.