FINAL YEAR PROJECT 1 (WEEK 6): Selection of ADC chips

Objectives:

1) To know the factors to consider when selecting the ADC chips

2) To find the differences between ADC 0804 and ADC 0809

Method:

1) By making in the internet

Analog-to-digital converters are among the most widely used devices for data acquisition. Digital computers use binary values but in the physical world everything is analog which means continuous signal. the example of physical quantities are temperature, pressure, humidity and many more and basically it is the physical quantities that we deal every day. The physical quantity is converted to electrical signals by using a device which is known as a transducers or sensors. Sensors for temperature, humidity, pressure and many other natural quantities produce an output that is voltage or current. Thus, we need to translate the analog signals to digital numbersby using analog-digital converter so that the microcontroller can read and process them. An ADC has n-bit resolution and this is shown in table below:

Vcc = 5V

The higher-resolution ADC provides a smaller steps size, where step size is the smallest change that can be discerned by an ADC. For now, we just only examine 8-bit ADC chips. Other factors that we need to consider when selecting the chips is the conversion time. Conversion time is the time taken for ADC to convert the analog input to a digital or binary number. The ADC chips either parallel or serial. In parallel ADC, 8 or more pins dedicated to bringing out the binary data but in serial ADC , it used only one pin to bringing out the binary data. For this project, the analog input channel must more than the digital output channel as it is used two sensors to connect with the ADC.

Next, to choose the suitable ADC chips for a project, we need to compare the ADC chips. For my project, I need to choose whether ADC 0804 chips or ADC 0809 chips so that the input signal that I used can read by using the ADC.  The result by comparing the ADC 0804 and ADC 0809 are shown below:

No./Type	ADC 0804	ADC 0809
1)	Can only take single analog signal.	Can be used to take up to 8 different analog signals.
2)	Does not have selector input pins.	Because the ADC 0809 can take up to 8 different analog signals, a multiplexer scheme is used to select the 8 different analog channels. Thus, it has 3 selector input pins.
3)	The ADC 0804 control signals are WR*,INTR* and RD* signals which are read all active low signals.	The ADC 0809 control signals are called SC, ALE, EOC and OE which are active high signals except EOC.
4)	Have one reference voltage (Vref/2).	Have two reference voltage (Vref+ and Vref-).
5)	Use INTR pin for end of conversion.	Use EOC for end of conversion.
6)	Reading the data using RD pin.	Reading the data use OE pin.
7)	The speed of conversion cannot be faster than 110 per second.	The speed of conversion cannot be faster than 100 micro second.

Notes:
a) WR (Write)
b) INTR (Interrupt)
c) RD (Read)
d) SC (Start Conversion)
e) ALE (Address Latch Enable)
f) EOC (End of Conversion)
g) OE (Output Enable)

Conclusion:

This week I am going to tell about the differences of ADC chips and the factors that we need to consider when selecting the ADC chips as it is very important when we need to convert our analog input signal to digital signal so that we can read the signal. From this research, I learned that if we have many analog input signals, we need to use ADC 0809 as it has 8 input analog channel compared to ADC 0804. For this project, I used two sensors to connect with the ADC which are temperature sensor and pressure sensor. So, by using the right components, it can reduce the cost to implement the project rather than used try and error process to check whether the components is suitable or not for this project.