28-02-2015, 11:41 AM
inerfacing of gas sensor with 89c51 rd2 microcontroller programming
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interfacing adc to 8051
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inerfacing of gas sensor with 89c51 rd2 microcontroller programming
10-03-2017, 04:05 PM
ADC is the analog-to-digital converter, which converts analog data into digital format; It is usually used to convert analog voltage into digital format. The analog signal has an infinite number of values as a sine wave or our speech, the ADC converts them into particular levels or states, which can be measured in numbers as a physical quantity. Instead of continuous conversion, ADC converts the data periodically, which is commonly known as sampling rate. The phone modem is one of the examples of ADC, which is used for Internet, which converts analog data into digital data, so the computer can understand, because the computer can only understand digital data. The main advantage of using ADC is that noise can be efficiently removed from the original signal and the digital signal can travel more efficiently than analog. That is the reason why digital audio is very clear while listening.
ADC0808 is one of the useful chips of National Semiconductor. See in the figure given to one side. In many embedded systems, microcontrollers need to take analog inputs. Most sensors and transducers such as temperature, humidity, pressure, are analog. For the interconnection of these sensors to microcontrollers it is necessary to convert the analog output of these sensors to digital so that the controller can read it. Some microcontrollers have built in analog-to-digital converter (ADC) so there is no need for external ADC. For drivers that do not have external ADC ADC is used.
One of the most commonly used ADCs is ADC0808. The ADC 0808 is a successive approximation type with 8 channels, that is, you can directly access 8 analog signals at one end. ADC0808 has an 8-bit data output as the ADC804. The 8 analog input channels are multiplexed and selected according to the table below the I / O pins using three A, B and C direction pins.
In ADC0808, Vref (+) and Vref (-) set the reference voltage. If Vref (-) = Gnd and Vref (+) = 5V, the step size is 5V / 256 = 19.53mV. Therefore, to obtain a step size of 10mV we need to establish Vref (+) = 2.56V and Vref (-) = Gnd. From the figure given below from ADC0808, note the ALE pins. We use the A, B and C directions to select IN0 - IN7 and activate ALE to block the address. SC is for startup conversion. SC is the same as the WR pin on other ADC chips. EOC is for the end of the conversion, and OE is to enable the output (READ). The EOC and OE are the same as the INTR and RD pins respectively.
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