June 28, 2013

Analog to Digital Converter – basics

Starting with this, we will try to understand basics of ADC ( Analog to Digital converter ) and DAC ( Digital to Analog converter) in layman’s terms. As far as Electronics is concerned it is basically divided into 2 kind of electronics – Analog & Digital.

Analog –

Analog generally refers to real world situations where any quantity is measured from minimum to highest level. It can be anywhere in between. For example, let us say we want to measure the wind speed. Well it can be still air that is 0 wind speed or on a very windy day it can be 100. It can be anywhere in between. Thus the speed here we are referring is an analog quantity. The same can be applied to many parameters like Light, Temperature, Pressure etc.

Digital –

While Digital refers to all kind of electronics that is handled by Digital ICs ( Integrated Circuits). In the world of Digital Electronics, everything is measured in 0 or 1. That is to say Yes or No. There are only 2 levels of quantity. It is either 0 or 1. Take for example – if someone asks you ” is it 2’0 clock ?” You have to say either yes or no. You can not say ” Oh, it is little bit 2 o’clock. Do you ? The same way Digital electronics understands only 0 & 1 or High & Low. Every information is converted into 0 & 1.

Now, the question arises – if we want to measure any physical parameter like Temperature with the help of a Microcontroller – a very complex digital IC how can we do it ? Temperature is a analog quantity while microcontroller understands only digital information. So how can we do it ? There should be something that can convert analog quantity into digital form which can be understood by microcontrollers.

Analog to digital converter IC is such a device or integrated circuit that will get the input from appropriate sensors and convert that information to digital form 0s & 1s. Sensors are  devices that can measure physical quantity and translate the measurement into electrical format. This can be voltage or current. This voltage/current output is then provided to ADC chip which convert it into its digital equivalent information. Now a days you can get sensors for measuring any kind of parameters like Temperature, Pressure, light, Speed, Rotation, Magnetism etc. You can measure any physical parameter with the help of sensors.

sensors iknowvations
Various kind of sensors

The output information of these ADC chips is in Number of Bits like 8 bits, 10 bits, 12 bits 16,18,20 &24 bits. Bit is a unit of Digital Information. Group of 4 bits is called Nibble while  group of 8 bits is referred as Byte. This Bits & Bytes are represented in Binary & HEX notation. 8 bits in Binary – a Byte in Hex  represent 256 in decimal notation. Every additional bit represent double than previous value. Thus 10 bits represents 256*2*2 = 1024 in decimal.

Now coming back to ADC, 8 bit ADC means when any sensor is connected to ADC, it will convert input parameter to 256 different values & provide this information to another chip. For example we want to measure temperature inside our kitchen oven. This temp may very from 0 to 250 degree centigrade. How can we measure this temperature ?

analog digital converter converters iknowvations
Well, this kind of system will be as under. A temperature sensor like Thermocouple or RTD is connected to ADC chip. This ADC chip is connected to a microcontroller and this is connected to Digital Display. Temperature Sensor converts the temperature inside of oven to a voltage. This voltage is converted to 256 different divisions by ADC. This means roughly 1 division per 1 degree centigrade. This, the ability to measure a minimum part of temperature is also called Resolution of the system. As we can only measure minimum one part, the resolution is one degree of this system. Now what if we use 10 bit ADC ? We will have 1024 different divisions. Now we can measure roughly 256/1024 = 0.25 degree Centigrade. So as we go for higher bit ADC we get more resolution. Though this is not as easy as it looks. We will look more in detail in our latter parts of this series.

With the advent of electronics, many microcontrollers have now inbuilt ADC. This reduces system errors and becomes easy for manufacturing of a system. In next part of this series we will understand more of Analog to Digital Converters. This will also help you to understand working of R242 – RS232 based Data Acquisition Card & U452 – USB based Data Acquisition Card.

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