Alarm Sounds When Refrigerator Door Remains Open Too Long Design Review 1 By Chi-Weng Kam Dan Strengier May 20, 2009

Original Design Idea – Refrigerator Alarm Issue with the original design: ◦ High Power Dissipation through the AC-DC Rectifier – heating of the Zener Diode. ◦ High AC Voltage Operation; Require certain technical knowledge in order to retrofit the circuit to the refrigerator – Not User Friendly. Babu, T.A. "Alarm Sounds When Refrigerator Door Remains Open Too Long." Electronic Design 26 Mar Apr

Design Requirements (Version 1) Modify the design idea of refrigerator alarm into a more user-friendly and sustainable product. Alert users when the refrigerator door remains open for more than 20 seconds (using audible, but reasonable alarm sounds). Use less power than the original design (replacing the AC-operated circuit into a DC-operated circuit). Create a product that is safe and easy to use, also small in size (wire space, length). No interface with the refrigerator 120V circuit (using DC battery as the mean). There will be no need for the user to change the refrigerator circuitry. Proper Operation inside the refrigerator (maybe the freezer). Babu, T.A. "Alarm Sounds When Refrigerator Door Remains Open Too Long." Electronic Design 26 Mar Apr

Design Specifications (Version 1) Sound level of the alarm is between 70dB and 80dB. DC battery operation (between 3-10V). Minimum space requirement (3'' X 5'' X 0.5'') with wire length (1 feet max if wire is used) Cost ($4.00 for the prototype, not including the cost of batteries) Babu, T.A. "Alarm Sounds When Refrigerator Door Remains Open Too Long." Electronic Design 26 Mar Apr Sound Levels: Design Priorities: 1. Safety (modify from AC-powered circuit to a DC-powered circuit) 2. Power Dissipation 3. Cost 4. Ease of use 5. Size

Component Selection and Design Refrigerator Door Sensor: Mechanical Switch (button) ◦ place the button on the edge of refrigerator door; activates the alarm circuit when the button is released; Optical Switch (Infrared Emitter and Sensor) Magnetic Switch Proximity Sensor Light Detector (using Phototransistor or Photodiodes) Sharp Phototransistor/ Photodiodes Circuit AppNote

Component Selection and Design The Timer Circuit: 555 Timer ◦ Upper limit of timer is 100s. Circuit requires 20s ◦ More external components Counting Chip 4060B ◦ AC buzzer requires 2 diodes ◦ DC buzzer requires 0 diodes Microcontroller IC 4060B Timer /Counter Datasheet: < >

Component Selection and Design User Alarms: Visual ◦ Strobing, bright light.  Adds complexity to design.  Probably not effective in adequately alerting user Aural ◦ Audio speaker  Requires audio-driving circuit. ◦ Piezoelectric Buzzer  AC Buzzer - requires square wave signal at approximately 2500 Hz  DC Buzzer – requires DC voltage, generates its own AC signal internally. Costs more than AC buzzer.

Questions? Feedbacks and Suggestions

How effective it is? Babu, T.A. "Alarm Sounds When Refrigerator Door Remains Open Too Long." Electronic Design 26 Mar Apr Therefore, It only takes about 24kWh energy saved over the lifetime of the refrigerator to breakeven with the cost of the circuit. More importantly, it reduces 23.28kg of CO 2 emission at the same time Certainly, in order for this calculation to be fair, we also need to consider the carbon footprint of producing each electronic components and its associated waste. Also, we need to account for the energy it takes to power the circuits. Cost Estimates: ComponentPrice IC 4060B$0.50 Buzzer$1.00 Transistor$0.50 R, C and D$0.10 each Total$3.30 Energy Saved: Cost of Electricity: $0.14 per kWh Amount of CO2 emissions reduced per kWh saved: 970g of CO 2 emission from coal-fired power plant Assume the circuit goes on 10 minutes a day, the energy the circuit consumed over a year is 0.072kWh, which is % of the typical annual refrigerator consumption.