Transcript Refrigerator Alarm Design Review Chi Dan

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. 2009. 06 Apr. 2009
<http://electronicdesign.com/Articles/ArticleID/20806/20806.html>
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)

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)
Design Priorities:
1.
2.
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4.
5.
Safety (modify from AC-powered circuit to a DC-powered circuit)
Power Dissipation
Cost
Ease of use
Size
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>
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;
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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 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 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