Alarm Sounds When Refrigerator Alarm Sounds When Refrigerator Door Remains Open Too LongDoor Remains Open Too Long

Design Review 1

By

Chi-Weng Kam

Dan Strengier

May 20, 2009

Original Design Idea – Refrigerator Original Design Idea – Refrigerator AlarmAlarm

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. 2009. 06 Apr. 2009 <http://electronicdesign.com/Articles/ArticleID/20806/20806.html>

Design Requirements (Version 1)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. 2009. 06 Apr. 2009 <http://electronicdesign.com/Articles/ArticleID/20806/20806.html>

Design Specifications (Version 1)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. 2009. 06 Apr. 2009 <http://electronicdesign.com/Articles/ArticleID/20806/20806.html>

Sound Levels: < http://www.eie.fceia.unr.edu.ar/~acustica/comite/soundlev.htm>

Design Priorities: 1. Safety (modify from AC-powered circuit to a DC-powered

circuit)2. Power Dissipation3. Cost4. Ease of use5. Size

Component Selection and DesignComponent 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 < http://www.physics.csbsju.edu/~awhitten/reference/Sharp_photodevices.pdf >

Component Selection and DesignComponent 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: < http://sigma.octopart.com/12954/datasheet/ON-Semiconductor-MC14060BCP.pdf>

Component Selection and DesignComponent 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?Questions?Feedbacks and SuggestionsFeedbacks and Suggestions