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A new PIC was born ! Welcome PIC32 :)

The News - Semiconductor news
Written by Bogdan
Microchip Technology Inc. announced the PIC32 family of 32-bit microcontrollers (MCUs). The PIC32 family adds more performance and more memory while maintaining pin, peripheral and software compatibility with Microchip’s 16-bit MCU/DSC families. To further ease migration and protect tool investments, the PIC32 family is fully supported by Microchip’s free MPLAB^® Integrated Development Environment (IDE). The MPLAB IDE offers unprecedented compatibility by supporting Microchip’s complete portfolio of 8-, 16- and 32-bit devices. “As a world leader in embedded-control solutions, Microchip is introducing the PIC32 family to build on the success of our vast 8- and 16-bit portfolio and offer customers a seamless migration path that bridges product families,” said Ganesh Moorthy, executive vice president of Microchip. “We provide designers with the most compatible environment in the industry for developing systems with 8-, 16-, and 32-bit MCUs!” Consumers’ desire for ever-more engaging end products is driving system requirements for increased memory capacity, performance and functionality. Launching with seven general-purpose members, the PIC32 family operates at up to 72 MHz and offers ample code- and data-space capabilities with up to 512 KB Flash and 32 KB RAM. The PIC32 family also includes a rich set of integrated peripherals, significantly reducing total design complexity and cost. Examples include a variety of communication peripherals, a 16-bit Parallel Master Port supporting additional memory and displays, as well as a single-supply on-chip voltage regulator. “Microchip brings a new perspective to the ever-growing 32-bit microcontroller market, born of their tremendous success in the 8-bit market,” said Tom Starnes, processor analyst at semiconductor market research firm Objective Analysis. “The peripheral-compatible PIC32 family should bring comfort to Microchip’s customers, knowing that the headroom is available as their applications evolve.” The PIC32 family is based on the industry-standard MIPS32^® architecture, with its leading combination of high performance, low power consumption, fast interrupt response and extensive industry tool support. The high-performance MIPS32 M4K^® core can achieve best-in-class 1.5 DMIPS/MHz operation, due to its efficient instruction-set architecture, 5-stage pipeline, hardware multiply/accumulate unit and up to 8 sets of 32 core registers. To reduce system cost, the PIC32 supports MIPS16e™ 16 bit ISA—enabling code-size reductions of up to 40%. “In the hands of the architects at Microchip, the MIPS architecture will do well in 32-bit MCUs,” said Max Baron, principal analyst at In-Stat. “Microchip gets a great architecture, while MIPS gets to be part of a series of MCUs from a company that is very successful in the MCU market. It’s a win-win for both companies.”
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Wheatstone bridge

Electronics lessons - General electronics

Written by Sergiu

Wheatstone bridge

A Wheatstone bridge is a measuring instrument invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. It is used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Its operation is similar to the original potentiometer except that in potentiometer circuits the meter used is a sensitive galvanometer.

Wheatstone's bridge circuit diagram.

In the circuit at right, $R x$ is the unknown resistance to be measured; $R 1$ , $R 2$ and $R 3$ are resistors of known resistance and the resistance of $R 2$ is adjustable. If the ratio of the two resistances in the known leg $(R 2 / R 1)$ is equal to the ratio of the two in the unknown leg $(R x / R 3)$ , then the voltage between the two midpoints will be zero and no current will flow between the midpoints. $R 2$ is varied until this condition is reached. The current direction indicates if $R 2$ is too high or too low.

Detecting zero current can be done to extremely high accuracy (see Galvanometer). Therefore, if $R 1$ , $R 2$ and $R 3$ are known to high precision, then $R x$ can be measured to high precision. Very small changes in $R x$ disrupt the balance and are readily detected.

If the bridge is balanced, which means that the current through the galvanometer $R g$ is equal to zero, the equivalent resistance of the circuit between the source voltage terminals is:

$R 1 + R 2$ in parallel with $R 3 + R x$

$R_E = {{(R_1 + R_2) \cdot (R_3 + R_x)}\over{R_1 + R_2 + R_3 + R_x}}$

Alternatively, if $R 1$ , $R 2$ , and $R 3$ are known, but $R 2$ is not adjustable, the voltage or current flow through the meter can be used to calculate the value of $R x$ , using Kirchhoff's circuit laws (also known as Kirchhoff's rules). This setup is frequently used in strain gauge and Resistance Temperature Detector measurements, as it is usually faster to read a voltage level off a meter than to adjust a resistance to zero the voltage.

Derivation

First, we can use the first Kirchhoff rule to find the currents in junctions B and D:

$I_3\ - I_x\ - I_g\ =\ 0$

$I_1\ + I_g\ - I_2\ =\ 0$

Then, we use Kirchhoff's second rule for finding the voltage in the loops ABD and BCD:

$I_3 \cdot R_3 + I_g \cdot R_g - I_1 \cdot R_1 = 0$

$I_x \cdot R_x - I_2 \cdot R_2 - I_g \cdot R_g = 0$

The bridge is balanced and $I g = 0$ , so we can rewrite the second set of equations:

$I_3 \cdot R_3 = I_1 \cdot R_1$

$I_x \cdot R_x = I_2 \cdot R_2$

Then, we divide the equations and rearrange them, giving:

$R_x = {{R_2 \cdot I_2 \cdot I_3 \cdot R_3}\over{R_1 \cdot I_1 \cdot I_x}}$

From the first rule, we know that $I 3 = I x$ and $I 1 = I 2$ . The desired value of $R x$ is now known to be given as:

$R_x = {{R_3 \cdot R_2}\over{R_1}}$

If all four resistor values and the supply voltage ( $V s$ ) are known, the voltage across the bridge ( $V$ ) can be found by working out the voltage from each potential divider and subtracting one from the other. The equation for this is:

$V = {{R_x}\over{R_3 + R_x}}V_s - {{R_2}\over{R_1 + R_2}}V_s$

This can be simplified to:

$V = \left({{R_x}\over{R_3 + R_x}} - {{R_2}\over{R_1 + R_2}}\right)V_s$

The Wheatstone bridge illustrates the concept of a difference measurement, which can be extremely accurate. Variations on the Wheatstone bridge can be used to measure capacitance, inductance, impedance and other quantities, such as the amount of combustible gases in a sample, with an explosimeter. The Kelvin Double bridge was one specially adapted for measuring very low resistances. This was invented in 1861 by William Thomson, Lord Kelvin.

The concept was extended to alternating current measurements by James Clerk Maxwell in 1865 and further improved by Alan Blumlein in about 1926.

External links

efunda Wheatstone article

Voltage divider

Electronics lessons - General electronics

Written by Sergiu

Voltage divider

In electronics, a voltage divider is a simple device designed to create a voltage (V_out) which is proportional to another voltage (V_in). It is commonly used to create a reference voltage, and may also used as a signal attenuator at low frequencies. Voltage dividers are also known by the terms resistor divider and potential divider.

Resistor divider

A voltage divider referenced to ground is created by connecting two resistors as shown in the following diagram:

The output voltage V_out is related to V_in as follows:

$V_\mathrm{out} = \frac{R_2}{R_1+R_2} \cdot V_\mathrm{in}$

It may be useful to note that R₁ and R₂ may each be comprised of many resistors in series.

As a simple example, if R₁ = R₂ then

$V_\mathrm{out} = \frac{1}{2} \cdot V_\mathrm{in}$

As a more specific and/or practical example, if V_out=6V and V_in=9V (both commonly used voltages), then:

$\frac{V_\mathrm{out}}{V_\mathrm{in}} = \frac{R_2}{R_1+R_2} = \frac{6}{9} = \frac{2}{3}$

and by solving using algebra, R₂ must be twice the value of R₁.

Any ratio between 0 and 1 is possible. That is, using resistors alone it is not possible to either reverse the voltage or increase V_out above V_in

Voltage divider as a voltage source

While voltage dividers may be used to produce very precise reference voltages, they make very poor voltage sources. This is because if a load is connected between the output voltage and ground the effective resistance between V_out and ground decreases. A change in the resistance of R₂ changes the load voltage, an undesirable situation for a voltage source.

In terms of the above equation, if current flows into a load resistance (through V_out), that load resistance must be considered in parallel with R₂ to determine the voltage at V_out. In this case, the voltage at V_out is calculated as follows:

$V_\mathrm{out} = \frac{R_2 \| R_\mathrm{L}}{R_1+R_2 \| R_\mathrm{L}} \cdot V_\mathrm{in} = \frac{R_2}{R_1+R_2+\frac{R_1R_2}{R_\mathrm{L}}} \cdot V_\mathrm{in}$

where R_L is a load resistor in parallel with R₂.

Note that for high impedence loads it is possible to use a voltage divider as a voltage source, as long as R₁ and R₂ have very small values compared to the load. This technique is rarely used, as the power disipated in such a divider would be considerable.

Use of voltage dividers

Voltage dividers are often used to produce stable reference voltages. These reference voltages may be used at a device with a high input impedence, such as an op-amp without fear of loading the divider. Alternatively, the reference voltage may be used to set the voltage being produced by a voltage source. A simple way of doing this (for low power applications) is to simply input the reference voltage into the non-inverting input of an op-amp buffer.

Impedance divider

A voltage divider is usually thought of as two resistors, but for electronics signals at a given frequency capacitors, inductors, or any combined impedance can be used. For general impedances Z₁ and Z₂, the voltage becomes

$V_\mathrm{out} = \frac{Z_2}{Z_1+Z_2} \cdot V_\mathrm{in}$

For instance, a divider can be made with a resistor and capacitor:

The resistor's impedance is simply its resistance:

Z R = R

The capacitor's impedance is a large resistance at low frequencies and a low resistance at high frequencies. The exact formula is:

$Z_\mathrm{C} = {1 \over j \omega C}$

where j is the imaginary unit, and ω is frequency in radians per second. This divider will then have the voltage ratio:

${V_\mathrm{out} \over V_\mathrm{in}} = {Z_\mathrm{C} \over Z_\mathrm{C} + Z_\mathrm{R}} = {{1 \over j \omega C} \over {1 \over j \omega C} + R} = {1 \over 1 + R j \omega C}$

The ratio then depends on frequency, in this case decreasing as frequency increases. This circuit is, in fact, a basic (first-order) lowpass filter, or, in the world of audio, a treble-cut filter. The ratio contains an imaginary number, and actually contains both the amplitude and phase shift information of the filter. To extract just the amplitude ratio, calculate the magnitude of the ratio, or just use the reactance of the capacitor instead of the impedance.

External links

Calculator: voltage divider - loaded and open circuit

References

Paul Horowitz and Winfield Hill, The Art of Electronics, Cambridge University Press, 1989.

More...

Electrical impedance

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