Adaptive ECG artefact noise cancelling using accelerometer

Electro-cardiographic examination may be performed not only from patients who is laying or sitting down peacefully, but also under stress conditions as some deceases may be detected when patient isn’t in the rest. For this ECG should be measured when patient is actively moving. We know that ECH signal is very weak among various artefacts. Motion artefacts are ones who is hard to filter out using regular methods. Various researches show that motion artefacts may be extracted by using accelerometers. Accelerometer reads motion pattern which is simultaneously analysed and filtered out from ECG using adaptive filtering algorithms including Least Mean Squares (LMS), Recursive Least Squares (RLS) As we mentioned – motion artefacts disturb the ECG signal so that it is almost impossible to recognize ECG pattern. And it is really hard to eliminate it and extract valuable information because artefact spectrum overlaps with ECG spectrum. And worse – noise spectrum changes all the time as movement may be not the same. So it is logical to measure the motion pattern with separate sensor – single or multiple axis accelerometer and use adaptive filtering technique to remove noise caused by motion.

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What is worst-case timing analysis

Probably many of you PC hardware people have faced similar problems when assembling computer from different parts and it seemed to work properly. But under some circumstances system just crashes without any known reason. Even in my practice I had a sound-card that that works well, but time at the time it just crashes and then computer hangs. Of course I can blame drivers or operating system, but there is another probability that there can some timing failures occur. There are lots of complex production around us that may have a number of undefined failures due to lack of timing worst-case analysis. Failures may occur due to power supply fluctuations, thermal changes or other conditions. Worst-case analysis encounter all available information of condition variations that can affect performance of components. Worst-case analysis shows if electronic design meets specifications under variable conditions like temperature, voltage or other variables. Only detailed analysis can prove if design will work reliable under all operating conditions. An it is proved that it is much better to design reliable hardware than fix the problems later. In many ways worst-case analysis may be implemented in various manufacturing phases automatically. By including several simple tests may save lots…

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Electronic design and development process

There are so many ways of designing and developing of electronic devices, that it is hard to think which would fit your needs and desires. But there are common steps that probably fit in most cases that allow to implement the electronic system from top to bottom: 1) Defining the requirements of electronic system; 2) Collecting information on components to be used; 3) Evaluate the components with respect to the requirements; 4) Block diagram of preliminary design; 5) Do a preliminary timing and load analysis; 6) Define functionality logic; 7) Draw schematic using CAD software; 8) Do device design and simulation; 9) Perform detailed timing analysis and simulation and adjusting the design; 10) Double-check signal loadings, buffering as needed; 11) Document the design and generate a net list and bill of materials; 12) Generate layout of a printed circuit board; 13) Prototype design; 14) Program the memories and programmable logic for testing. 15) Debug and verify operations using oscilloscope/logic analyser or other debugging tools; 16) Update and complete documentation as the design changes. Those are general steps and the order may vary or even several tasks may be performed in parallel. Usually software is written in parallel with hardware design…

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Chemical effects of electricity

Electronics depend on chemistry more than you can imagine. In order to generate electricity there are many methods used, one of them is chemical. Remember batteries, where electricity is generated because of chemical reactions inside cell. Also in conductors like liquids and gases electricity is carried not by electrons as it is in solid constructions(copper, aluminum, etc.), but by ions – molecules with electric charges. Even non distiled water contain enough ions to be conductive. Lets go through several chemical effects of electricity. Electrolysis Electrolysis is a decomposition of liquid compound by passing electric current through liquid called electrolyte(salt water, copper sulphate, sulphuric acid). Electrolysis is used very widely in industry like electroplating of metals, refining of copper and extraction of aluminum from ore. To make electrolysis happen there are two conductors used cathode(-) and anode(-).  

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Circular buffers in DSP processors

I am not going to analyse what DSP processors are different from regular microcontrollers as there are many differences that allow to boost performance in many specific tasks like filtering, FFT, etc. One thing is obvious that DSP processors have to perform mathematical calculations rapidly enough to get predictive results. Better result we want – more processing power wee need. We know that MCU are performing two main tasks: data manipulation and mathematical operations. But fact is that it has to be done really fast. General purpose microcontrollers aren’t optimised to perform these tasks effectively as microcontroller has to as much universal as possible to fit in many areas. In other words flexibility reduces performance. DSP processors are more specialized microprocessors that ara optimised for tas that they usually do – multiplication and addition. Lets take most common DSP routine FIR digital filter implementation. It takes several samples of signal x[] and produces output signal y[] which is modified by multiplying appropriate samples by coefficients an . y[n] = a0x[n]+a1x[n-1]+…+akx[n-k]

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Automated electronic CAD systems overview

More and more design operations become automated. These changes give many benefits like effectiveness, minimal errors and less routine operations to designers. Modern electronic equipment require very precise planning as devices shrink to minimal sizes, operation power increases and also have to fit to it external design requirement. So designing is a very complex task where without smart CAD software would be almost impossible to do. When designing a new electronic device you have to deal with several areas that is necessary to make device reliable and attractive device. All of these areas usually are done on particular CAD system. Most common CAD based electronic specific task are: Mixed Analog-digital device modeling; Programmable Logic modelling and synthesis; HF circuits and electromagnetic modeling; Functional modeling; PCB Design; Thermal modeling; Chip topology modeling. Each of these modeling and designing processes require different skills and knowledge. Lets go through each to see their specifics and what CAD systems are used to automate related tasks.

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32 bit microcontrollers from ATMEL with ARM7 core

Somehow I’ve been sticked to NXP LPC2xxx series microcontrollers and left other brands behind. There are many major manufacturers of ARM microcontrollers. One of them that is worth to pay attention is Atmel with its AT91SAM7 (Smart ARM7) series. SAM7 series of microcontrollers have built in Flash memory and data memory as well. Core is powered with 1.8V while peripherals need 3.3V. Core voltage is converted inside the chip so you don’t have to bother about this and only apply stabile 3.3V voltage. SAM7 microcontrollers are based on ARM7 core so they have very good performance characteristics. SAM7 microcontrollers differ from other brands with their ability to access memory directly (DMA), so each microcontroller peripheral have distinct two channel controller. LPC series only have AMBA bridge between AHB and LHB. Main characteristics of AT91SAM7 series: very good ratio between performance and poer consumption; performance up to 60MIPS; ARM/THUM command support; 32 byte data bus; programmable external 8/16/32 byte data bus; multiple channel DMA; SPI interface – four CS(Chip Select) pins; TWI interface; Built-in RC generator and PLL; Expanded clock generator and power consumption control; 4 external clock sources; Interrupt controller with extended functions; Debugging interface; RTC with distinct interrupts; 2…

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