Electrical signal power and energy calculations by example

In electronics and signal processing you have to deal with electrical signals. In many cases you may need to calculate signal power and energy. –it is easy with DC In standard situation when DC power supply is applied to known resistor or other device like LED, motor you can calculate its power very easy by applying Ohms law: If we rung this device for time T then we can calculate total energy used: In some cases you may not know the resistance of your circuit. In this case you can measure the current flow. So your power formula can be transformed by using same Ohms law:

Continue reading

Using wavelet transform in biomedical engineering – heart signal analysis

As we mentioned before, wavelet transform is used to analyze short time and non-stationary signals. Since base wavelet function has to parameters – translation and scaling, it is possible to achieve good time and frequency localization. In other words, we can equally analyze slow signal and fast signal structures without losing resolution and so evaluate signal frequency characteristics and time dynamics. Heart signal analysis is one of the most common problem in biomedical engineering. Practically every part of ECG signal carries some sort of information about heart condition, possible pathologies, and deceases. So equally frequency and timing characteristics of ECG signal is important. As you know standard ECG signal consists of several typical waveforms like P-QRS-T where in P and T waves low frequency component dominates and in QRS mid and high. The common condition of hear is myocardial ischemia when blood flow through coronary arteries to heart is reduced…

Continue reading

Wavelet transform – the basics

Recently I’ve been reviewing wavelet transform. I think some points are worth sharing. In this first post I would like to mention the basics of wavelet transform and its main features. Probably most important question that comes to mind is why we need another transform when we already have Fourier transform. The answer lies in the signals that we want to analyze. If we take any periodic signal that is stationary (e.g. Pulse train) then Fourier transform is the right tool, because its frequency components doesn’t change in time. Let’s take another case when signal changes in time (chirp signal). Classical Fourier transform cannot determine frequency components of such signal, because it doesn’t carry any information about signal time scale. Of course it is possible to cheat with Short Time Fourier Transform (STFT), when signal is analyzed in short chunks, but again there is a problem of resolution – the…

Continue reading

About Digital Signal Processing

Today, signals i.e. quantities that fluctuate over a period of time with usually with high frequency have acquired a great amount of importance and are being used in many fields especially in communication. Digital signal processing involves conversion of digital data into signals thus, making its transfer easier and subsequently converting these signals back into the original form. A signal has many characteristics or domains such as time domain, spatial domain, frequency, wavelet domain etc. Any one among these can be used to process a respective signal. From among these, the engineer usually selects the one that best represents the characteristics of the signal concerned or in other words, the one from which data can be obtained easily. In order to ascertain the required characteristic, the engineer may try out many among these properties. The use of signals has gone up especially with the use of computers. Computers are capable…

Continue reading

Encoding and modulation of digital signals

We know that digital signals are stored as binary numbers in memory cells. Let’s see how these digital signals can be transferred in other words – how they can be encoded in to electrical signal shape. When signal has to be sent it has to be modulated. Pulse Code Modulation (PCM) Probably simplest and most common modulation method is pulse code modulation (PCM). In CPM coding information is modulated as voltage levels. If supply voltage is 5V, then binary”1″ is represented as +5V while 0 as 0V level. Only two voltage levels are used to modulate signal. Signal can be sent in parallel (bus mode) or serial mode. In parallel mode whole (let’s say 8 bit) signal can be sent at once via 8 wires, while in serial mode data has to be sampled in time. This transmission method is most popular in embedded systems, for instance, ADC sends converted…

Continue reading

DSP processors and their characteristics

The processing of the various signals is carried out through implements that are together called as DSP hardware. This includes the hardware that is used for transmission of signals, various devices that are used to enhance or filter the signals, analogue to digital and digital to analogue converters and other processing equipment such as computers. Among the hardware mentioned above, digital signal processors are the ones in which the actual processing takes place. Usually the digital signal processors today have the following characteristics: They are equipped to handle real time processing i.e. they can give the optimal performance even when streaming data is being fed into them. The memories that are used to store programs are different from the ones used to store data. They do not provide hardware that supports multitasking. It can be used as a direct memory access device in supporting or host environments. They take analogue…

Continue reading

Digital Signal Processing – Applications

Digital signal processing is the technique used to analyse various digital signals and obtain information form the same. It is also used for transfer of information from one place to another and also involves conversion in between analogue and digital signals. It finds its application in various areas ranging from broadcasting to medicine. Let us have a look at some of the applications of the same. Biomedical Applications: DSP is used extensively in the field of biomedicine. In it, the various signals that are generated by the different organs in the human body are measured in order to find information regarding the health of the same. For example, in case of electrocardiograms, the electric signals generated by the heart are measured. Similarly, the activity of the brain is monitored by electroencephalograms. Automatic Control: These days, many gadgets are available that can perform their tasks automatically. These devices contain various components…

Continue reading