## How does tri-state buffers work

Those who work with microcontrollers probably know about data buses. Only one device(memory, peripherals) connected to the bus can work at one moment. Only one unit can directly connect to the bus beside the CPU, which usually is a host. So decoding circuit determines the desired unit and connects it to the bus. Other devices are effectively disconnected so that they wouldn’t have any effect on bus operations. Tri-state buffers carry them out. Tristate buffers allow isolating circuits from the data bus. This means that circuit is switched to a high impedance state. Usually, we know dual state circuits with two logical levels, “0” and “1”. But there is also widely used tristate logic, where it can switch I/O to a high impedance state. Tristate logic can simply be made by two transistors: Using such a circuit we can have the following output results according to input variations: Q1 Q2 Output OFF OFF High Impedance OFF ON 0V ON OFF +5V Simply speaking when the output pin is in a high impedance state it is physically disconnected from the circuit.

## Using Gray code for rotary encoders

Gray code is well known and widely used in angular movement systems where angular positions have to be known. Gray code encoder can be constructed pretty easily by masked wheel where tracks are read with photocells. Did you look at the picture and thought for yourself that gray code is the same binary code. Well, no… the main problem with binary systems was using binary code in tracks; there are many positions where several tracks change state simultaneously. This may result in an error. Actually, in gray code, only one track can change at the same time during rotation. So then, if an error occurs, the resulting error will be only one bit. Gray code is easy to convert to binary this task can be done by any microcontroller using a lookup table:

## Nonlinearity and span of transducers

When the developer selects a transducer for their projects, they have to look through various parameters and then select the part that best fits the design needs. This time let’s look at some transducer characteristics that can be found in specifications. Transducer Range First of all, let’s clear out what is a range of a transducer. The range is understood as maximum and minimum input and output signal. For instance, we can take a simple thermal sensor which input range can be from -50 to 120ºC and output range of 0 to 5V. The range can be understood as measured signal range and working environment parameters like working temperature range, power supply voltage range, etc. Full-scale deflection – Span Span is the maximum variation in the input or output. Span can variate due to an error that is mostly linear and can be adjusted. Span error is measured in percents, which shows how much the output value is different from the correct value. Another linear error close to span error is zero offset. This error occurs because of calibration errors or other changes like aging or environmental conditions change. Zero offset error is a constant overall range. It can be…

## X-10 interface for home automation projects

Simply speaking X10 protocol allows transmitting data over power lines. X10 uses a PLC(Power Line Carrier) technology. How does this work? The specification says that each time a 60Hz AC signal crosses the zero line,, a 120kHz burst is is transmitted with a duration of 1ms. One crossing burst forms one information bit. Simply speaking if we needs to form â€œ1â€ you need to burst at the first crossing but not at second and for â€œ0â€ is reversed pattern – you need to burst at the second cross but none on first.

## DIY 4x22W car audio amplifier based on TDA7384

I decided to make a pretty simple but powerful enough audio amplifier. For this, I’ve chosen quad-bridge car audio amplifier IC – TDA7384, which has four input and four output channels with a power capability of 4x35W. If connected to a car battery where the operating voltage is about 13.2V, then each channel can give 22W what is more than enough for me. This amplifier I probably will use to test audio processor TDA7313, which is still in the development phase. I didn’t find much information about this chip on the internet, so I decided to build it and try it independently.

Firmware for AduC70xx ARM microcontrollers can be uploaded using a built-in boot-loader. To work with boot-loader, Analog Devices offer a small free program, ARMWSD working under the windows system. The program doesn’t require installation. ARMED communicates with AduC70xx via COM-port. Simple programming steps looks like this: Connect target board to PC COM port; Go to Configure->Parts and select AduC part: Then go to Configure->Comms and select serial port and baud rate:

## Integral Hall sensors

Hall sensors are common sensors of many measuring devices, including linear or angular motion, magnetic field, current, etc. The main convenience of hall sensors is that they don’t have to be mechanically connected to objects. They are also simple, cheap, which makes them attractive in the automotive, manufacturing, and aviation industries. Many manufacturers produce hall sensors: Honeywell, Melexis, Allegro Microsystems, Micronas Intermetall, Siemens, Analog Devices, etc. A typical circuit for connecting Hall sensors One of the simplest is linear Hall sensors that are used for measuring magnetic field strength. Integral hall sensors include a sensor signal amplifier, also temperature compensation, and supply stabilization circuits. Sensor output signal voltage and polarity depend on magnetic field strength and direction. If there is no magnetic field near the sensor, then output is equal to zero. To achieve this differential amplifier has to be used, characteristics will be corrected to be output voltage zero when there is no magnetic field. Other groups of hall sensors have comparator built-in. This allows having digital level signals on output. There can be two types of such hall devices: switches and triggers.

## Protection circuits for operational amplifiers

In the 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 a 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 ones have. Today popular operational amplifiers have internal protection circuits built-in, and this makes designers’ life much easier. But protection elements lowers some operational amplifiers like operation speed, dynamic range, and output signal swing level. Because of this, some operational amplifiers may not have internal protection circuits. In this case, you have to take care of it.

## 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 the control element. Dissipated power is approximately equal to I(Vin-Vout). There is another way to generate a regulated voltage. The method is different from the previous one. A transistor operates as a saturated switch in a switching regulator, 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 the output voltage with reference and this way changes oscillators pulse width or frequency.

## Dual polarity power supply source

Most op-amp circuits run from the symmetrical bipolar supply source, let’s say ±15V. The simplest way to generate symmetrical split supplies is to use a pair of 3 terminal voltage regulators. For instance, let’s 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 a voltage divider, which consists of two higher accuracy resistors: