Integral Hall sensors

Hall sensors are common sensors of many types measuring devices including linear or angular motion, magnetic field, current, etc. main convenience of hall sensors is that they don’t have to be mechanically connected to object. Also they are simple, cheap that makes them attractive in many industries like automotive, manufacturing, aviation. There are manu manufacturers who produce hall sensors: Honaywell, Melexis, Allegro Microsystems, Micronas Intermetall, Siemens, Analog Devices, etc. One of simplest are linear Hall sensors, that are used for measuring magnetic field strength. Integral hall sensors include sensor signal amplifier, also temperature compensation and supply stabilisation circuits. Sensor output signal voltage and polarity depends on magnetic field strength and direction. If there is no magnetic field near sensor, then output is equal to zero.   To achieve this differential amplifier has to be used, then characteristics will be corrected to be output voltage zero when there is no magnetic field. Other group of hall sensors have comparator built in. This allows to have digital level signals on output. There can be two types of such hall devices: switches and triggers. Unipolar Hall switch acts as unipolar device which is “OFF” if there is no magnetic field or it’s direction…

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Protection circuits for operational amplifiers

In specifications of operational amplifiers there are maximum limits of allowed voltages on pins. Maximum currents are limited as well. So voltage and current they both limit allowed dissipated power Pmax=Umax*Imax. In well designed circuits Op Amps should have protection circuits from various overloads like short circuit, high common phase voltage level in differential inputs, electrostatic charges, etc. Earlier operational amplifiers didn’t have built in protection circuits while modern have. Today popular operational amplifiers have internal protection circuits built in and this makes designers life much easier. But protection elements lowers some characteristics of operational amplifiers like operation speed, dynamic range, output signal swing level. Because of this some of operational amplifiers may not have internal protection circuits. In this case you have to take care of it.   Protection from high differential voltage input When protecting Op Amps from high voltage inputs usually there are protecting diodes connected between input pins.       In normal operation (linear mode) when signal input level is up to mV the resistance of diodes is few mega-ohms. Practically diodes have no influence to input signal. But when input voltages opens diodes, then input voltage will be limited to few mili-volts (p-n junction…

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Switching step-up and step-down regulators

All regular voltage regulators (like 7805) have several disadvantages like output voltage is always lower than input and some power is dissipated in control element. Dissipated power is approximately equal to I(Vin-Vout). There is another way to generate regulated voltage. Method is different from previous. In switching regulator a transistor operates as a saturated switch which periodically applies the full unregulated voltage across an inductor in short intervals. During each pulse inductor current builds up storing energy on its magnetic field:   Inductor also smooths the output voltage. Feedback circuit with comparator compares output voltage with reference and this way changes oscillators pulse width or frequency. Switching regulators have few attractive properties that made them popular. Low power dissipation even if there is a large drop from input to output; switching regulators may generate output voltages higher than unregulated input; they can generate opposite polarity than input; switching regulators can be designed to run directly from AC power line with no power transformer. This way modern DC supplies are lightweight. As na example you can take computer power supply block. But… Switching supplies have side effect- they generate noise and can put hash back to power line. But these problems…

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Dual polarity power supply source

Most of op-amp circuits run from symmetrical bipolar supply source lets say ±15V. The simplest way to generate symmetrical split supplies is to use a pair of 3 terminal voltage regulators. For instance lets take two voltage regulators: 7815 and 7915.   If you need an adjustable variant of dual polarity regulated voltage source you can use 317 and 337 adjustable regulators, where you can trim voltage with voltage divider which consists of two higher accuracy resistors:   You may wander if there are dual 3 terminal regulators in one casing – yes they are. They are called “Dual Tracking Regulators”. Dual tracking regulators are available as complete integrated circuits in both – fixed and adjustable versions. Typically there are 4195 for fixed ±15V and 4194 is symmetrically adjustable via single resistor.

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Electrical switches principles and switching problems

Switches are important part in electronic systems. It is one of most frequently used human interaction with electronic devices methods. But switches are mechanical component that are vital part of any equipment. Electrical switches Electrical switches are as old as electricity. The function is always the same – it makes or breaks current in a circuit. In early 19th switches were used for DC circuits, while later for AC and then they serves for switching wide spectra signals starting from audio and ending with digital. Well switches have changed comparing to those before 100 year, but principal is the same old as electric itself. When switch connects circuit path it has a resistance of mΩ, when current path is broken, then resistance is high MΩ and higher. This resistance and maximum voltage that can be applied to insulation is often major important and vital feature that leads to switch stability. Contact resistance Switch resistance is determined by switch contacts – the moving metal parts which touch when switch is ON. The amount of contact resistance depends on the area of contact, contact material, the amount of force that presses the contacts together and the way that force have been applied.…

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Overview of noises in electronic systems

There are several sources of noises in electronic systems. Noises are unwanted signal polluting random or not signals that reduces overall signal quality. Thermal Johnson/Nyquist noise This noise is actually discovered by two scientists Johnson who did the experiments and Nyquist who developed the formula. Thermal noise present at all frequencies (has a constant power density at all spectra) and is so called white noise. This noise can only be reduces by reducing temperature, resistance and bandwidth. Lets see at the Noise voltage RMSformula: VRMS=(4·k·T·R·Δf)1/2 where k – Boltzmanns constant (1.38·10-23J/K); T – Absolute temperature (K); R – Resistance (Ω); Δf – Bandwidth (Hz). For example if we have 10kΩ resistor at 300K. Bandwidth 10kHz then we get VRMS=1.3μV. Shot noise This type of noise occur because of random charges moving across potential barrier. I2n= 2·e·I·Δf where e- charge of electron (1.6·10-19C); I – DC signal current (A)’ In – Noise current (A); Δf – Bandwidth (Hz). Usually Shot noise is more due to high frequency component. So reducing bandwidth may reduce high frequency noise. Flicker Noise This noise increase due to decreasing frequency. So measuring sensitive measurements ir is better use DC. Flicker noise origins isn’t known and not…

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Long range directional microphones-myth and reality

There are a lot of myths about directed long-range microphones. You can here like they can reach distances of 100, 200 and more meters, others say that this is a myth and these numbers are commercial purposes. Let us try mathematically find proof and see the real situation. Introduction to long-range microphones When talking about directed microphones, usually we have in mind that sound sources are in the open air, and there are no reverberation effects. So the only factor is the distance of the sound source object from the microphone. Along the distance, sound power drops significantly, and in longer ranges, it interferes with other sounds like wind and other noises in the atmosphere. When the distance is about 100m sound pressure drops more than 40dB(comparing to a distance equal to 1m). If the sound level is 60dB then from 100m, you will hear 20dB. Sound level 20dB is less than other environmental noise, and many standard microphones are not sensitive enough for such sound level. So we can say that directed microphones must have: High sensitivity and selectivity from environment noises even if they have a higher level than real sound; High directivity to for excluding noise signals…

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