CEPD News 
February, 2011 - Vol 4, Issue 1


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In This Issue
Power Over Ethernet
Elementary Radio
IIR Filters
Quick Links

Power Over Ethernet
Power over Ethernet (POE) is a method of passing electrical power and data over Ethernet cabling.  The power typically comes from a device such as an Ethernet Switch or may be may be injected using a midspan power supply.  A POE splitter can be used on the receiving end to split out the power and data to be used by the receiving device or the POE device may have the splitting capability built inside the device.  The Power over Ethernet standard is defined in IEEE 802.3at-2009. 
To find out more about the standard, visit the IEEE website at: http://standards.ieee.org/findstds/standard/802.3at-2009.html
Advantages of using POE:
 Wire runs can be longer than USB and provide Gigibit data speeds that USB does not have.
 Cat-5 does not have the restrictions of new AC wiring when wiring in a home or office.
  POE devices can be used independent of local AC systems making them more globally portable.
 Power can be provided from a single source with UPS capability, so each POE device does not need a UPS.

Some applications for POE type devices include remote webcam/ security cameras, VoIP phones, network routers and wireless access points.  In all these applications, the amount of wiring is reduced by combining the power and data over the Ethernet wiring.  POE devices provide a set resistance, so POE switches know that a POE device is present.  This detection method allows the POE switch to decide whether it should provide power to the device.
Elementary School Students Build Crystal Radios
David Farrell presented a hands-on workshop for students at Mountain View Elementary School in Broomfield on January 27th.  The students each built a crystal radio to receive AM broadcasts with no power.  The purpose was to spark the interest of the students in electronics and to promote science and engineering to students of a young age.  Dave related that when he was their age, his first electronic project was a crystal radio receiver, which eventually lead him to a career in Electrical Engineering.  To view the presentation for information on obtaining crystal radio parts and building your own, click on this Crystal Radio Set link.
Why average when you can filter?

Noise is a common issue in embedded systems. Software engineers are often tempted to use simple averaging to perform a filtering task in software, but this can consume valuable RAM space and real-time in a small processor. It is essentially an FIR filter with coefficients of 1/N. Simple averaging may not provide as aggressive a stop band as a designed FIR or IIR filter. Adding a digital IIR filter is a quick and easy alternative.


Digital filters can be implemented with either floating point or fixed point math. This example uses floating point. While floating point is simpler, it is not always possible due to code size or processor speed requirements. In addition, a fixed-point solution can be used in an FPGA, which can be advantageous. Fixed point solutions will be explored in our next newsletter. Stay tuned!

The first-order IIR filter form can be expressed as follows:
The implementation of the actual floating point filter in C is comprised of just three lines of code: 

  w0 = (input - (a1 * w1)); /* Calculate w0 term */

  output  = w0 * b0;        /* Calculate output value (b1=0) */

  w1 = w0;                  /* Save w1 term for next calculation */


Note that, as with any A/D converter, an anti-aliasing filter is still recommended at the A/D input even if a digital filter is being used.

For the full code example, please follow this code example link. Follow the filter design calculations and frequency response link to determine coefficient values. 


If you would like help developing a new product or if you find your project understaffed, CEPD can help you meet your deadlines. Our staff draws on years of diverse product design experience to provide creative and timely solutions for your product needs. Some of our specialties include:
  • DSP
  • Embedded Systems Hardware and Software
  • Data Acquisition
  • Wireless Sensor and Telemetry Systems (Zigbee, Cellular, VHF, Bluetooth, ANT+, etc.)
  • Control Systems
  • Programmable Logic: FPGA / CPLD / EPLD
  • Analog Circuit Design
  • Switching Power Supply Design
  • Battery charging (all chemistries)
  • PCB Design and Layout
  • Analysis and Documentation
Our goal is to provide cost effective and expedient design options for our clients. Our services range from an hour of consultation to large turn-key product development projects. We provide detailed proposals, accurate estimates and time schedules to help you manage each phase of the project. We can offer fixed cost or time and materials proposals to suit your specific needs. There is no cost to you for the initial proposal we create and the initial discussion required! 

The Staff of CEPD, Inc.
2011, CEPD, Inc.             
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