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Understanding and calculating decibels

A decibel is a special unit that is a little different from other measuring units in everyday practices. This is a nonphysical unit but more mathematical understanding. Decibel (dB) units are similar to percent (%), just different calculations and purposes. As a percent unit, so decibels are used to compare two quantities as the whole value in percents is expressed as 100%, so decibels are more complex, and it is a ratio of two independent quantities. Decibels are mostly used for energetic parameters like power or voltage and current. Decibel (dB), equal to 0.1 bel (B) . Bel – is a decimal logarithm of the ratio of two powers. If these powers P1 and P2, then the expression looks like this:

Low frequency Butterworth and optimal Wiener ECG filters

Regular ad hoc filters don’t guarantee optimal signal filtering as there are no criteria that evaluate filter characteristics. Usually, filter parameters are calculated empirically, and the best results do filtering. To avoid such a shortage, there are optimal filters used where some criteria optimize parameters. Optimal filtering’s main idea is to give bigger weight coefficients to signal spectra parts where signal noise has less power, and true signal spectral components have bigger power. Let’s project a simple Butterworth filter used as a comparative filter to optimal Wiener DSP filter.Butterworth filter transfer characteristics: Where N indicates filter Tap number. I will skip the Butterworth filter description as the main idea is constructing an optimal Wiener filter. Butterworth filter characteristics are pretty plain: The main disadvantage of the Butterworth filter is that signal is distorted on filter output. If you want minimal signal distortions it is better to use an optimal Wiener filter. Filter chart looks as follows:

24×24 LED dot matrix display control

24×24 LED display is formed using nine 8×8 Dot LED matrix displays connected to AT90S2313 MCU. MCU scans an indicator line in series. A special PC program is written to draw images on the screen and transfer them via a COM port to the device. You can send pictures in series that gives an animation effect. Device circuit:

PCB Exposure using UV light LED box

I came across this interesting project. The guy decided to make a UV PCB exposure box made of UV light LEDs. The main reason why he used LED was the power dissipation and compactness. Assuming that one UV tube would take about 6W while one UV LED would take about (20mAx3.2V=64mW). Most of that energy UV tubes dissipate as heat energy. So he took: 54 x UV LEDs of 400nm (6000 – 7000 mcd) – 100 units in Ebay costed 12€;18 x 68ohms resistors 1/4W – 0,36 €;1 connector – 0.50€;1 electrolytic condenser of 2200uF – 30v;1 Eurocard Plate 100×160 about 5 € ;

Compact dual oscillator and power on reset for MCU

Would you consider connecting an IC with a dual-speed oscillator and a power-on reset to your MCU? This is what MAX7378 does. This is a good replacement for ceramic resonators, crystals, and other oscillator modules, and discrete reset circuits. The good thing here is that at any time, you can select either low-frequency 32.768kHz or a high frequency from range 600kHz to 10MHz.The clock frequency can be switched at any time without glitches. MAX7378 can be powered from 2,7V to 5,5V, so it is suitable for most MCU types. Comparing to Crystal resonators, it is resistive to vibrations and EMI. It is a good solution for the automotive and industrial environment. High-frequency oscillator error reaches ±2% at 25°C at 5V power supply. In other words, speaking oscillator frequency stability is about ±325ppm (when crystal stability is from ±10ppm to ±100ppm). So it doesn’t correspond to crystal accuracy, but it suits most non-time-critical applications. 32.768kHz oscillator is more accurate with an error of 1%, but it still a bit much for time measurements.

IR remote control signal receiver using AVR microcontroller

IR remote control is a device you can find everywhere to find a TV, VCR, or home theatre. Why not use one of them for controlling your own devices like light, air conditioning, etc. As we know, remote control devices use IR light. This is invisible light of about 950nm wavelength. One most significant problem in using IR light is that there many other sources of it like the sun, light bulbs, fire. To exclude other sources, the IR signal is modulated by some frequency. The receiver has to be tuned for this frequency. Mostly remote controls transmit IR signals using 36kHz frequency signals. Transmitting and coding is one part that can be done more efficiently than receiving and decoding. Decoding is usually performed by using microcontrollers. First of all, the receiver has to get rid of the 36kHz carrier frequency. This is not a simple task to demodulate the signal; this is why particular IR receiver IC’s are produced. One of them is TSOP1736:

Characteristics of sensors and transducers

A sensor or transducer is a device that converts one type of energy to another – usually electric. They are used for various purposes, including measurement or information transfer. Generally speaking, a sensor or transducer is a device that converts a signal from one to another. Let’s go through transducer characteristics that describe the performance of sensors. One of the characteristics that describe the functional relationship between physical input and electrical output is the Transfer Function, which shows the relationship between the input and output signal. Depending on the details of this characteristic, it may be a complete description of sensor characteristics. The transfer function may be used as a calibration curve. For instance, let’s take an example of the infrared temperature sensor.

Generate true random numbers on microcontroller

Sometimes there is really a problem of how to generate truly random numbers using your microcontroller. Usually, a computer processor or any other MCU can generate a Pseudo-Random Number (PRN). These numbers are generated by algorithms, so-called Pseudo-Random Number Generators (PRNG). Everything that a pure algorithm produces is predictable at some level. Many PRNG algorithms generate random numbers, but there is always a defined number of iterations when a random number sequence will repeat itself. Sometimes it may be acceptable. One popular way to generate pseudo-random numbers is using Timers. The universal algorithm is the concept of the Linear Feedback Shift Register (LFSR). LSFR is an n -bit register initiated with a non-zero seed value and is clocked by shifting values to the left and loading a new bit into bit0. The new bit is calculated by XORing the bits of selected taps of LSFR. This method is used in rand() functions.

Neural networks and artificial intelligence in robotics

When talking about artificial intelligence(AI), many people think that neural nets should be as intelligent as the human brain. Some people don’t even imagine how widely they are used in their life. Let’s narrow us to something more simple and understandable. The most exciting usage of AI is robotics. Today isn’t tough to build a simple robot with a few sensors and a couple of motors. But the harder part is to make it react to the real-world as you expect it to be. When programming the robot brain, there is checking sensor states and reacting to particular circumstances like hitting the wall, line on the ground, etc. But more sensors robot has more complex reactions may be. Programming of more complex systems may be painful without using simple neural networks.

AVR-DDS signal generator in-line ASM explained

I have got a couple of questions (in fact, not the first ones) for the AVR DDS generator I have built: “that’s all the asm code that I don’t understand. Could you explain it? Is it possible to do it with inline asm (only in C)?” I decided to explain this part more deeply because it took me to figure this all out. First of all, what we have to do, it is to implement simple DDS algorithm. In a few words, Direct Digital Synthesis(DDS) is known as a Numerically Controlled Oscillator. Simple rule: NCO-based DDS is a point(memory location)-skipping technique (and a constant interpolation of the stored signal) and runs at continuous update(clock)-rate. As the DDS output frequency is increased, the number of samples per waveform cycle decreases. Practically speaking, let’s have some math. We have a clock generator connected to MCU. In my case, F_CPU=16000000Hz. This is our Clock In.