Difference between revisions of "S15: RFID Security Box"

Revision as of 02:47, 15 April 2015

Grading Criteria

Project Title

Abstract

The RFID Security Box is a container with an electronic lock that can be unlocked by using RFID tags, NFC-compatible devices, or a manually entered passcode.

Objectives & Introduction

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A security box for storing valuables that is accessible through a numeric keypad, NFC-compatible device, and RFID tags, tokens, and cards.

• NFC/RFID Controller breakout board
• Lock-style Solenoid
• 3x4 Phone-style Matrix Keypad
• RGB LCD Screen

Team Members & Responsibilities

• Rajwinder Ruprai
• Charles MacDonald

Schedule

Show a simple table or figures that show your scheduled as planned before you started working on the project. Then in another table column, write down the actual schedule so that readers can see the planned vs. actual goals. The point of the schedule is for readers to assess how to pace themselves if they are doing a similar project.

Parts List & Cost

Give a simple list of the cost of your project broken down by components. Do not write long stories here.

Design & Implementation

The design section can go over your hardware and software design. Organize this section using sub-sections that go over your design and implementation.

Hardware Design

Initial rough draft of system architecture / schematic diagram (external link):

• https://www.dropbox.com/s/1jhlvk78qywjkfu/244_project.jpg?dl=0

Hardware Interface

The buses are allocated as follows:

• PN532 (RFID/NFC transmitter/receiver) is configurable to use RS-232, SPI, or I2C via jumpers.
• LCD is configurable to use SPI or I2C via jumpers.
• LCD RGB backlight uses three GPIOs
• Solenoid uses one GPIO
• Piezo buzzer uses one GPIO.
• Keypad matrix uses multiple GPIOs (connections TBD).

Software Design

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Implementation

This section includes implementation, but again, not the details, just the high level. For example, you can list the steps it takes to communicate over a sensor, or the steps needed to write a page of memory onto SPI Flash. You can include sub-sections for each of your component implementation.

Testing & Technical Challenges

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Include sub-sections that list out a problem and solution, such as:

Issue #1 : Backlight control

The LCD panel has a RGB backlight consisting of a single RGB LED, that has a common anode and three independent cathodes. Each cathode has a 200-ohm resistor in series to limit current to 25mA (when +5V supplied to the anode) per LED. In order to control the red, green, and blue channels of the backlight independently, a circuit is required that can interface GPIOs from the SJOne board to the cathode such that 25mA can be sunk per cathode. This amount of current to sink in order to fully turn on a single LED is beyond the limit of the LPC1758 ability, so a direct connection is not possible.

The solution is to use a Darlington transistor. The ULN2803 contains eight independent Darlington transistors, each of which having the appropriate base and collector resistors to be controlled by the SJOne GPIOs directly (being TTL/CMOS compatible). This chip can sink 500mA per transistor which meets and exceeds the current requirements of the RGB backlight.

Interfacing the backlight controls to three GPIOs will provide 2^3=8 total colors. However we will use the PWM function of the LPC1758 to to increase the range of available colors to several hundred thousand. This will also allow software-defined brightness control, to either set the brightness to a user-defined level or for strobing or flashing effects on the display by modulating the brightness over time.

Issue #2 : Power supply

The solenoid requires 12V, the SJOne board uses 3.3V, and the LCD backlight requires 5V. In order to meet this requirement a power supply circuit was designed with the goal of keeping efficiency high and heat output low.

A switching PSU is used to convert 120V AC to 12V DC for the solenoid. The 12V is fed into a switching 5V regulator to provide 5V for the LCD backlight. Note that the relatively large voltage drop from 12V to 5V does not cause excessive heat due to the switching regulator being used, thus no heatsinking or other cooling methods are required. Finally, the 5V is fed into a 3.3V linear regulator. At this point the voltage drop is relatively small (approx. 2V) and the corresponding heat dissipation is low.

In this way all three power rails (3.3V, 5V, and 12V) can be provided to the system. The least efficient part is the 3.3V linear regulator, but the switching 5V regulator and switching 12V PSU are highly efficient in terms of conversion.

Conclusion

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Project Video

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Project Source Code

• Sourceforge Source Code Link

References

Acknowledgement

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References Used

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Appendix

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