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=Sustainability Analysis for "Capacitive Proximity Sensor Provides Accuracy And Speed"=


 * Link
 * Quick Background
 * The 4 E's
 * Energy
 * Environment
 * Economics
 * Equity
 * Green Engineering Design Principle
 * References

Link:
[|Electronic Design] [|Schematic]

Quick Background:
The link to the schematic is above. The first stage of the circuit creates a square wave pulse. The components in the author’s schematic create a 100 kHz square wave pulse. The next stage in the circuit creates a delay to the D flip flop. The potentiometer for calibration of the amount of delay on one line. The sensor causes a delay change on the other line. The line with the potentiometer is adjusted so that the rising edge to the clock of the D flip flop is just after the rising edge of the sensor line. This will cause the output to be high when there’s no object sensed. When an object goes in contact with the sensor, there will be an added capacitance to the sensor line. This will cause a greater delay and make the rising edge of the sensor line appear after the rising edge of the clock line. This will cause the output to be low.

The potentiometer can adjust the sensitivity of the circuit; depending on how close the rising edges are set. The sensitivity can also be set based on the size of the sensor. The larger the sensor pad is, the more sensitive the circuit will be. This is because a larger sensor will have a greater capacitance compared to a smaller sensor pad.

Energy:
The proximity sensor mentioned in the article uses very little energy compared to the system it is normally integrated in. The amount of power the design uses will range in the micro watts. Normally, this design integrates with a microcontroller which would mean that it draws the power from whatever source the microcontroller is powered with. This could range from batteries for portable devices to wall outlet AC to DC converters. Since the energy source varies greatly, there can be many ways to make the energy sources renewable. This is heavily dependent on what source a designer decides to use. This design focuses on minimal component counts which does help when talking about energy consumption and efficiencies as well. Fewer components generally results in lower energy consumptions.

Environment:
The proximity sensor can be used in a variety of applications. Some applications, such as using the sensor as a simple switch, can be detrimental to the environment in the sense that it takes more resources to manufacture a proximity sensor than it does a switch. Other applications, such as a close range proximity sensor, can benefit from this design because other methods utilizes more components or takes up more space. An example of a different proximity sensor is the ultrasonic sensor. This utilizes sound to determine the proximity of an object. Both methods work for proximity sensing, however, the capacitive sensor requires less components and energy to accomplish the same goal as the ultrasonic sensor. Ultrasonic sensors may also effect certain animals that can hear the ultrasonic frequencies that the humans can not. This may effect the way the animals behave if the sensor is used in an environment with a lot of different species.

Economics:
The proximity sensor is a simple, minimal cost design to implement. The design can be embedded within a microcontroller or used as a stand alone circuit. The implementation of the circuit is very simple so most hobbyists can implement the sensor well under $5. The Schmitt-Trigger chip, 74LVC1G14, cost approximately $0.50 and the D Flip-flop cost about $0.20. Costs can be further reduced if the design is integrated into a single chip. The only issue with this design is the calibration portion which may require the user to manually adjust the settings for the correct sensitivity readings. This issue can be eliminated if potentiometer is replaced with a fixed resistor adjusted to the optimal value that allows for minimal changes due to external interferences such as temperature. In order to acquire the nominal resistor value, a lot of testing is involved which can increase the cost prior to releasing the product. At the end of life of the product, the components can either be reused or scrapped. Ideally, the chips can be de-soldered and reused in another similar application.

Equity:
Capacitive proximity sensors can impact a wide range of stakeholders since the applications for a proximity sensor is very general. Consumer products like cell phones or laptops utilize proximity sensors for their single button touch sensors. In general, companies that build products on the systems level can utilize the sensors. The sensors provide a more user appealing product that involves less mechanical movement. Consumers benefit from this because they can use products and companies benefit from the money gained from selling the product. Some companies may have more benefits from capacitive proximity sensors than others based on the applications the sensors are used in.

Green Engineering Design Principles:

 * 1) Engineer processes and products holistically, use systems analysis, and integrate environmental impact assessment tools.
 * Proximity sensors are only a small part of a whole system.
 * 1) Conserve and improve natural ecosystems while protecting human health and well-being.
 * Depending on the application of the proximity sensor, it can be utilized to improve the health and well-being of humans while still being eco-friendly. An example is to utilize the proximity sensor in bathrooms where germs can spread easily. They can also be used in replace of the lighting switches to minimize direct hand contact to the switch.
 * 1) Use life-cycle thinking in all engineering activities.
 * Normally the sensor pad is integrated to a PCB's layout. This minimizes component count to reduce the initial cost. End of life of the product, however, would result in a PCB that can not be reused easily since it has an application specific design on the layout. In order to improve this, designers must think about creating external sensor pads that can be removed from the old product and implemented to a new product.
 * 1) Ensure that all material and energy inputs and outputs are as inherently safe and benign as possible.
 * Generally, proximity sensors do not need to come in contact with the object that it's detecting. Also, the proximity sensor utilizes low DC voltages that will cause minimal to no harm to most object. This makes the general design of the proximity sensor safe.
 * 1) Minimize depletion of natural resources.
 * Since the design minimizes component count, it minimizes the use of resources. Reducing the use of resources further requires reducing the materials used in the manufacturing process of the chip or sensor pads.
 * 1) Strive to prevent waste.
 * Generally, the design is for specific applications which requires many different application specific layouts on PCB. For this reason, designers should strive to generalize the design so that parts can be reused in the future when the product line is at the end of it's life.
 * 1) Develop and apply engineering solutions, while being cognizant of local geography, aspirations, and cultures.
 * The capacitive proximity sensor is a very general design that can be implemented in any environment. The only part of the design that requires more designing based on the location or needs is the sensor pad. Larger sensor pads yield more sensitive sensing. Also, the shape or appearance of the sensor pad can be designed so that it's ascetically appealing in a room environment.
 * 1) Create engineering solutions beyond current or dominant technologies; improve, innovate, and invent (technologies) to achieve sustainability.
 * Different solutions to proximity sensing exist, however, current designs can always be improved for a more sustainable design. For instance, to take the current design further, a single chip can be developed to reduce the need to use to chips to achieve the capacitive proximity design.
 * 1) Actively engage communities and stakeholders in development of engineering solutions.
 * Since the proximity sensor may work differently in different environments, to find better solutions, it would be in the designer's best interest to seek local feedback about their system.

References:
Braun, David. "4E Sustainability Analysis." //HOME - Electrical Engineering Department - Cal Poly//. California Polytechnic State University. Web. 29 Apr. 2011. .

Braun, David. "EE413 Sustainability Analysis." //HOME - Electrical Engineering Department - Cal Poly//. California Polytechnic State University. Web. 29 Apr. 2011. .

Design, Electronic. "Capacitive Proximity Sensor Provides Accuracy And Speed." //Electronic Design Home Page//. 22 Oct. 2010. Web. 30 Apr. 2011. .

"Single D-type Flip-flop with Reset; Positive Edge Trigger (74LVC1G175)." //NXP Semiconductors//. Web. 29 Apr. 2011. .

"Single Schmitt-trigger (74LVC1G14)." //NXP Semiconductors//. Web. 29 Apr. 2011. .