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| In Electronic Design Notes 1 it
was mentioned we can control the current in electrical circuits using resistors. Of course, there are other means
to achieve current control, but resistors are simple, cheap, and efficient electronic components. Control is the true magic word in electronics. No matter what we do, the purpose is to take control of voltages, currents, frequencies, and of various functions. Once we achieve total control, then we can do whatever we can think of. There are few basic things we need to know about resistors, therefore they are listed summarily as follows: 1. Types of resistors 2. Useful formulas 3. Resistors color code chart 4. Equivalent series and parallel resistors 5. Controlling the voltage and current 6. Detecting current sense 7. Frequency control NOTE The basic notions highlighted in this page are related to electronic design topics presented in the first part Hardware Design of Learn Hardware Firmware and Software Design. |
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There is an incredible variety of resistors; in this page are presented only few main groups. First of all resistors are: A. fixed B. variable Depending on the way we insert them into electrical circuits, resistors can be: a. through hole (TH) b. surface mount (SM) c. various, mechanical fixtures Further, resistors are built as: 1. carbon composition 2. metal film 3. carbon film 4. wirewound Of course we could differentiate resistors based on the power (current) they can safely handle, but there are way too many types available. Variable resistors come in few particular types. They are important to note because each type requires specific schematics: 1. potentiometers 2. rheostats 3. decades 4. programmable potentiometers (details of hardware schematics and firmware programming source code are in Learn Hardware Firmware and software Design)
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In order to work with resistors we need few formulas; for example: 1. Resistance 2. Ohm's Law in DC circuits 3. Ohm's Law in AC circuits 4. Impedance 5. Resistance value at current temperature 6. Conductance 7. Electrical conductivity 8. DC power 9. Horse power conversion 10. Kilowatt to hp conversion 11. DC Energy 12. Efficiency
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Fixed resistors of the "through hole" type are marked using a special color code. The new SM (surface mount) types are marked with numbering systems specific to each manufacturer--please consult their Data Sheets.
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The equivalent of series resistors is calculated with: RT = Σ Ri The equivalent of parallel resistors is calculated with: 1/RT = Σ 1/Ri Calculation examples for three resistors:
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First thing, please take a look at Figs 4 and 5.
In Fig 4, we control voltage Ui using a "voltage divider" schematic.
We can even adjust Ui if we use a potentiometer schematic as we did in in Fig 1. The voltage divider
schematic allows for 2, 3,..n precise voltage levels to be supplied to the Load circuit. Adjacent are the formulas
needed to calculate the Ui value. |
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Please take a look at Fig 6.
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| In normal conditions V1 = 12 V, and V2
= 11.988 V (R1 = 1 KΩ). Those values are sent to the PIC controller Analog-to-Decimal channels 1 and 2
(randomly chosen). Next, we transform the analog voltages into their decimal equivalents, then we compare them
mathematically. The result is one of the following cases: V1 > V2 (Load is drawing power) V1 = V2 (Load is Open) V1 < V2 (Load is generating power) V2 = 0 (Load is short-circuited) If an accident happens and Load becomes generator, the current will change its sense, therefore V2 will become greater than V1: V2 > V1 Not only we are able to detect the sense of the current, but we know precisely how much current Load is drawing in each moment. Details about working with Microchip dsPIC controllers and about the ADC conversion function are in Learn Hardware Firmware and Software Design. |
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Frequency control is presented in Filters Design Notes. |
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comments regarding this page using support@corollarytheorems.com Page last updated on: March 15, 2008 © Corollary Theorems Ltd. All rights reserved. |
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