Wireless temperature monitoring system pdf
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Our Customers Include:. Food Service. Food Service Read More. Healthcare Read More. Life Sciences. Life Sciences Read More. Retail Read More. Get Started Now! In this experiment we will build a two-stage amplifier using two bipolar transistors. In most practical applications it is better to use an op-amp as a source of gain rather than to build an amplifier from discrete transistors.
A good understanding of transistor fundamentals is nevertheless essential. Because op-amps are built from transistors, a detailed understanding of opampbehavior, particularly input and output characteristics, must be based on an understanding of transistors.
We will learn in Experiments 9 and 10 about logic devices, which are the basic elements of computers and other digital devices. These integrated circuits are also made from transistors, and so the behavior of logic devices depends upon the behavior of transistors. In addition to the importance of transistors as components of op-amps, logic circuits, and an enormous variety of other integrated circuits, single transistors are still important in many applications.
For experiments they are especially useful as interface devices between integrated circuits and sensors, indicators, and other devices used to communicate with the outside world. The three terminals of a bipolar transistor are called the emitter, base, and collector Figure 7. A small current into the base controls a large current flow from the collector to the emitter.
The current at the base is typically one hundredth of the collector-emitter current. Moreover, the large current flow is almost independent of the voltage across the transistor from collector to emitter. We will begin by constructing a common emitter amplifier, which operates on this principle. A major fault of a single-stage common emitter amplifier is its high output impedance. This can be cured by adding an emitter follower as a second stage.
In this circuit the control signal is again applied at the base, but the output is taken from the emitter. The emitter voltage precisely follows the base voltage but more current is available from the emitter. The common emitter stage and the emitter follower stage are by far the most common transistor circuit configurations. Figure 7. The current flowing from collector to emitter is equal to the base current multiplied by a factor. An NPN transistor operates with the collector voltage at least a few tenths of a volt above the emitter voltage, and with a current flowing into the base.
The base-emitter junction then acts like a forward-biased diode with an 0. The constant of proportionality is called hFE because it is one of the "hparameters," a set of numbers that give a complete description of the small-signal properties of a transistor see Bugg Section It is important to keep in mind that hFE is not really a constant.
In the emitterfollowerstage the output emitter voltage is simply related to the input base voltage by a diode drop of about. An ac signal of 1 volt amplitude on the input will therefore give an AC signal of 1 volt on the output, i. As we will see later, the advantage of this circuit is as a buffer due to a relatively high input and low output impedance.
In the common emitter stage of figure 7. Although we are only looking to amplify the AC signal, it is nonetheless very important to set up proper dc bias conditions or quiescent points.
The first step is to fix the dc voltage of the base with a voltage divider R1 and R2 in Figure 7. The emitter voltage will then be 0. For an emitter follower, the collector is usually tied to the positive supply voltage VCC. First of all, the base bias voltage must be fixed by a low enough impedance so that changes in the base current do not alter the base voltage. This is essential because the base current depends on hFE and so is not a well determined quantity.
If the base voltage is determined by a divider as in Figure 7. Be careful that you do not exceed the maximum allowed power dissipation Pmax. Finally, the quiescent point determines the voltages at which the output will clip. For a common emitter stage the maximum output voltage will be close to the positive supply voltage VCC. The minimum output voltage occurs when the transistor saturates, which happens when the collector voltage is no longer at least a few tenths of a volt above the emitter voltage.
We usually try to design common emitter stages for symmetrical clipping, which means that the output can swing equal amounts above and below the quiescent point. The voltage gain of the emitter follower stage is very close to unity. In our circuit we use CE to bypass part of the emitter resistor at the signal frequency. For a common emitter, R would usually just be the emitter resistor, but for an emitter follower R might be the emitter resistor in parallel with the input impedance of the next stage.
If you want the input impedance of the whole stage, rather than just that looking into the base, you will have to consider rin in parallel with the base bias resistors. The output impedance of a common emitter stage is just equal to the collector resistor.
For our two-stage amplifier shown in Figure 7. Instead of using the current amplifier model, one can take the view that the collector current IC is controlled by the base-emitter voltage VBE. The dependence of IC on VBE is definitely not linear, rather it is a very rapid exponential function. The presence of the intrinsic emitter resistance re modifies the above Equations 1 — 4. Verify that the quiescent point has not changed significantly.
Observe the change in gain as you traverse the full range of the trimpot using 10 kHz sine waves. Start with the contact at ground bottom of diagram and move it up until CE bypasses all of RE. When approaching maximum gain turn down the input amplitude a long way so that the output signals are still well shaped sine waves.
If the output is distorted the amplifier is not in its linear regime, and our formulas for the ac gain are not correct. Do theory and experiment tend to converge as Vout tends to zero? What trimpot setting gives a gain of —25?. To see where the trimpot is set, remove it from the circuit and measure the resistance from cw to wiper or from ccw to wiper. What fraction of the original output amplitude do you see? Is this as expected?
What fraction of the original output do you now see? The emitter follower has unit gain, i. The input impedance is high and the output impedance is low. Ordinarily the quiescent base voltage is determined by a bias circuit. In the present case the collector voltage VC of the previous circuit already has a value suitable for biasing the follower, so a direct dc connection can be made between the two circuits. Assemble the emitter follower circuit shown in Figure 7.
Carry out appropriate dc diagnostic tests. Correct any problems before moving on. Confirm that the voltage gain of the emitter follower is unity. Drive the complete system with the function generator.
Observe the ac amplitudes at the input of the emitter follower and at the output. Measure the ac gain of the emitter follower stage. You may want to put the scope on ac coupling when you probe points with large dc offsets.
What fraction of the unloaded output do you now see? Compare with your calculations. Low cost is assured by trimming and calibration at the wafer level. The LM35's low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy.
It can be used with single power supplies, or with plus and minus supplies. The LM35D is also available in an 8-lead surface mount small outline package and a plastic TO package. LCs do not emit light directly. They are used in a wide range of applications including: computer monitors, television, instrument panels, aircraft cockpit displays, signage, etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones.
They are usually more compact, lightweight, portable, less expensive, more reliable, and easier on the eyes. They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they cannot suffer image burn-in. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. It is an electronically-modulated optical device made up of any number of pixels filled with liquid crystals and arrayed in front of a light source backlight or reflector to produce images in colour or monochrome.
The earliest discovery leading to the development of LCD technology, the discovery of liquid crystals, dates from With no actual liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second crossed polarizer.
In most of the cases the liquid crystal has double refraction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using, for example, a cloth. The direction of the liquid crystal alignment is then defined by the direction of rubbing. Typical uses of buzzers and beepers include alarms, timers and confirmation of user input such as a mouse click or keystroke.
A piezoelectric element may be driven by an oscillating electronic circuit or other audio signal source. Sounds commonly used to indicate that a button has been pressed are a click, a ring or a beep.
Electronic buzzers find many applications in modern days. It can also be referred to as a photoconductor. Aphotoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band.
The resulting free electron and its hole partner conduct electricity, thereby lowering resistance. A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, e.
In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons i.
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