Electronics Concepts PDF

FIGURE -2 The Thevenin's equivalent circuit of a sensor allows easy visualization of how loading occurs Figure -2 shows such an element modeled as a voltage Vx and a resistance Rx. Now suppose a load, RL, is connected across the output of the element as shown in Figure - 2...

FIGURE -2 The Thevenin's equivalent circuit of a sensor allows easy visualization of how loading occurs Figure -2 shows such an element modeled as a voltage Vx and a resistance Rx. Now suppose a load, RL, is connected across the output of the element as shown in Figure - 2. This could be the input resistance of an amplifier. A current will flow and voltage will be dropped across Rx. The loaded output voltage will thus be given by: The voltage that appears across the load is reduced by the voltage dropped across the internal resistance. This equation shows how the effects of loading can be reduced after making RL > RX. EXAMPLE 2.1 An amplifier outputs a voltage that is ten times the voltage on its input terminals. It has an input resistance of 10 kW. A sensor outputs a voltage proportional to temperature with a transfer function of 20mV/°C. The sensor has an output Solution the unloaded output of the sensor is simply VT = (20 mV/°C).50°C = 1.0 V. Since the amplifier has a gain of 10, the output of the amplifier appears to be Vout = 10Vin = (10)1.0 V = 10 V. But this is wrong, because of loading since a voltage dropped will appear across the output resistance of the sensor. The actual amplifier input voltage will be given by Equation (2.1), Where VT = 1.0 volts, so that Vin = 0.67 volts. Thus, the output of the amplifier is actually Vout = 10(0.67 V) = 6.7 V. 26 Analog and Digital Sound Representation: Signals When sound is transmitted, it may need to change form, without being destroyed. Sound moves fast: in air, at 340 m/sec. Its two important characteristics are Frequency and Amplitude. Frequency is measured in Hz. Humans can hear frequencies between 20 Hz and 20,000 Hz. Amplitude is measured in decibels. Consider music: 1. Sound is pressure waves in air, caused by drums, guitar strings… etc or vocal cords 2. Converted to electrical signals by a microphone 3. Converted to magnetism when it's put on master tape and edited 4. Converted to spots on a CD when CD is manufactured 5. Converted to electricity when played by CD player 6. Converted back to sound by a speaker A similar kind of story can be told about visual images (sequences of static images) stored on videotape or DVD and played on DVD player. Degradation Any time signals are transmitted; there will be some degrading of quality: 1. signals may fade with time and distance 2. signals may get combined with interference from other sources (static) 3. signals may be chopped up or lost 27 When we continue to transmit and transform signals, the effect is compounded. Think about photocopies of photocopies of photocopies... Example This is the transmitted signal: And this is the received signal (dashed) compared to the transmitted signal: The horizontal axis here is time. The vertical axis is some physical property of the signal, such as electrical voltage, pressure of a sound wave, or intensity of light. The degradation may not be immediately obvious, but there is a general lessening of strength and there is some noise added near the second peak. Analog Signals The pictures above are examples of analog signals: An analog signal varies some physical property, such as voltage, in proportion to the information that we are trying to transmit. Examples of analog technology: 28  1. photocopiers 2. telephones 3. audio tapes 4. televisions (intensity and color info per scan line) Analog signals always suffer from degradation. Digital Signals With a digital signal, we are using an analog signal to transmit numbers, which we convert into bits and then transmit the bits. A digital signal uses some physical property, such as voltage, to transmit a single bit of information. Suppose we want to transmit the number 6. In binary, that number is 110. We first decide that, say, "high" means1 and "low" means 0. Thus, 6 might look like: The line is the signal, which rises to the maximum to indicate a 1 and falls to the minimum to indicate a 0. Serial & Parallel Serial and parallel transmission mechanisms are two ways of sending a digital signal from A to B. A serial connection will send one line of data from transmitter to receiver. This method is electronically simpler, making it easier to determine what is going on, plus it's cheaper. It is, however, slower than parallel transmission. 29 Parallel transmission uses multiple lines of data to send more information more quickly. This method is more complex and more expensive than serial transmission. Also, it is usually only good for short distance transmissions of data. Computers process data in binary form, or base 2. The following table gives the binary equivalent values for 0-15 (decimal): Decimal Binary Decimal Binary 23 22 21 20 23 22 21 20 0 0 0 0 0 8 1 0 0 0 1 0 0 0 1 9 1 0 0 1 2 0 0 1 0 10 1 0 1 0 3 0 0 1 1 11 1 0 1 1 4 0 1 0 0 12 1 1 0 0 5 0 1 0 1 13 1 1 0 1 6 0 1 1 0 14 1 1 1 0 7 0 1 1 1 15 1 1 1 0 In a 4 line parallel connection, the decimal number 13 is communicated by sending one/on pulse along line 1 (2 3), one/on pulse along line 2 (22), zero/off pulse along line 3 (21)and one/on pulse along line 4 (2 0). Computer memory is defined in terms of Bits and Bytes. 1 Bit = one on/off space in memory (0 or 1). 1 Byte = 8 bits, and can therefore hold any decimal value from 0 (00000000) to 255 (11111111). 1 Kilobyte In fact, 1KB = 1024 bytes = 210 bytes. 1Megabyte = 1024 kilobytes, 1 Gigabyte = 1024 megabytes. One way of converting a decimal (base 10) number to a binary (base 2) number is by divide the decimal number by 2: 30  600 / 2 = 300 rem. 0