Echolocation with HC-SR04 ultrasonic distance sensor

Ultrasonic echolocation is common practice in many areas including nature itself. We all know how bats or dolphins navigate – they emit ultrasonic waves and depending on time delay of reflected echoes, they can determine the distance from obstacles or catch. From engineering perspective it is relatively easy to measure distances with ultrasound – all you need to know is sound speed in the air and time delay between sent and received pulses.

echolocation_principle

(Source: http://www.analog.com/)

 L = C_{AIR}\cdot \frac{t}{2}

L is the measured distance; CAIR – ultrasound speed; t – time between transmitted and received pulses.

The accuracy of measured distance mainly depends on air temperature. Approximately sound speed in air can be calculated by following formula:

 C_{AIR} = 20.0457\cdot \sqrt{273.15+T} (m/s)

For instance at 25ºC the speed of sound in dry air CAIR = 346.13 m/s. So if you want greater accuracy, you should also measure temperature to adjust sound speed. Continue reading

Ultrasound wave propagation and parameters

Ultrasound waves are acoustic pressure waves that interact with propagation media. Ultrasound visualization normally is based on wave reflectance from regions with different acoustic properties. When wave meets different acoustic media, part of it transmits further while other reflects. This happens due to different acoustic impedance. The ration between reflected and transmitted energy purely depends on difference of acoustic impedance in both regions.

transmit_reflect_ultrasound

As you can see each material can be characterized by its acoustic impedance Z which is equal to ultrasound speed v and material density r. Continue reading

Testing NEO-6M GPS receiver module

If your project require global positioning feature then you should use one of many GSP modules. There are many receiver modules and expansion boards available for your choice. They vary in PCB size, functionality, antennas used and price. In most cases you are probably looking for simple, small all in one solution where GPS receiver and antenna would be on same package.

neo-6m_gps_module

Recently I have picked one that might fit for most needs – GPS receiver NEO-6M module with ceramic antenna and TTL serial interface. It is very compact GPS module with most needed features: Continue reading

Technology can have positive impact on social interactions

Technology has impacted everyday life in many ways. Social interaction is one area where it has had profound impact. Thanks to technology, the world is now a tiny global village where anyone can connect with others around the world in seconds.

Consider the day to day life of today’s average individual. It normally begins with checking for messages from loved ones and work colleagues and catching up on events on social media to constantly keeping in touch with people across the globe through emails and instant messaging. The day often ends just as it started (checking social media and replying to messages) leaving the individual feeling happy, connected and fulfilled. This piece takes a closer look at the positive impact of technology on social interactions.

technology_impact

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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.

ECG_marked

The common condition of hear is myocardial ischemia when blood flow through coronary arteries to heart is reduced what prevents receiving enough oxygen. This can damage heart muscle and lead to heart attack. In order to notice this pathology it is we need to analyze S-T segment of ECG waveform. Insignificant changes in signal can indicate ischemia. In order to find the variations in signal it is needed to analyze signal up to 0,05Hz. Additionally QRS complex also carries some information. Due to ischemia there appears slight arrhythmia which has to be detected. Continue reading