Rainfall Measurement

In this project, rainfall measurement is the most challenging part as I want to make it simple yet reliable and efficient. Before I go with the method that I use to measure rainfall for this project, I'd like to share information about how meteorologist measure rainfall quantity.

Weather observers use more sophisticated instruments, known as rain gauges and tipping buckets to more precisely measure precipitation. Rain gauges have wide openings at the top for rainfall. The rain falls and is funneled into a narrow tube, one-tenth the diameter of the top of the gauge.It fills up with rain water, and the meteorologist then measures how much rain has fallen. Rainfall is measured in millimeters. It is usually described as light, moderate, or heavy rain, depending on how much has fallen. Zero millimeters of rain a day is no rain.

In simple way.....

This is how the rain gauge look like. 0 reading means no rain. Light rain, which is up to 2.5 millimeters of rainfall an hour, isn't very wet. Moderate rain measures 2.5 to 7.5 millimeters of rain an hour.If you're outside it would be wet enough without an umbrella or raincoat. If more than 7.5 millimetres of rain is falling an hour, meteorologists call it heavy rain.

For my project, applying the concept; I will use a tube or gauge to collect the rainfall while to measure the level I use Infra Red (IR) sensor. I'll put a floating material such as ping pong ball or a piece of polystyrene inside the gauge, when rainfall drops it will float and IR sensor will detect its distance.

Humidity Sensor: HSM 20G

Humidity can be measured in several ways, but Relative Humidity is the most common. In order to understand relative humidity, it is helpful to first understand absolute humidity. Absolute Humidity is the mass of water vapor divided by the mass of dry air in a volume of air at a given temperature. The hotter the air is, the more water it can contain. Relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity which depends on the current air temperature. A reading of 100 percent relative humidity means that the air is totally saturated with water vapor and cannot hold any more, creating the possibility of rain. This doesn't mean that the relative humidity must be 100 percent in order for it to rain. It must be 100 percent where the clouds are forming, but the relative humidity near the ground could be much less. 

HSM-20G is an analog sensor. If you go through the datasheet  of HSM-20G, you will find out that they have given output voltage data from the humidity sensor for certain relative humidity values and they have plotted a graph too.
Same with the Temperature Sensor this sensor too is connected to an ADC (analog to digital converter) in order to get the output in digital.

In order to use this sensor, a connector cable was build to connect the sensor to strip board. 4-pin header was connected to the circuit required such that:

• (-)  negative pin connects to GND
• (+) positive  pin connects to Vcc
• H (humidity sensor) pin which included 47µF capacitor and 100KΩ resistor and connects to ADC.

 

Measuring Humidity using HSM 20G

Humidity sensor is a device consisting of a special plastic material whose electrical characteristics change according to the amount of humidity in the air. Basically it is a sensor that senses the amount of water vapor in air. The module of HSM-20G is essential for those applications where the relative humidity can be converted
to standard voltage output. The humidity sensor module HSM-20G is shown in figure below.

Front View

Back View

Circuit Diagram with ADC

Temperature Sensor: LM35DZ

Why use LM35DZ

I choose this type of temperature sensor because of its following feature:

• Calibrated directly in ° Celsius (Centigrade)
• Linear + 10.0 mV/°C scale factor
• 0.5°C accuracy guaranteeable (at +25°C)
• Rated for full −55° to +150°C range
• Suitable for remote applications
• Low cost due to wafer-level trimming
• Operates from 4 to 30 volts
• Less than 60 μA current drain
• Low self-heating, 0.08°C in still air
• Nonlinearity only ±1⁄4°C typical
• Low impedance output, 0.1 W for 1 mA load

• It has an output voltage that is proportional to the Celsius temperature.
• The scale factor is .01V/^oC
• The LM35 does not require any external calibration or trimming and maintains an accuracy of  +/-0.4 ^oC at room temperature and +/- 0.8 ^oC over a range of 0 ^oC to +100 ^oC

Basic electrical connection

 

Here is a commonly used circuit.  For connections refer to the picture

• In this circuit, parameter values commonly used are:
• V_c = 4 to 30v
• 5v or 12 v are typical values used.
• R_a = V_c /10^-6
• Actually, it can range from 80 KW to 600 KW , but most just use 80 KW.
   

In this basic circuit, we will need to use a voltmeter to sense Vout. The output voltage is converted to temperature by  a simple conversion factor. The sensor has a sensitivity of 10mV / ^oC. Use a conversion factor that is the reciprocal, that is 100 ^oC/V. The general equation used to convert output voltage to temperature is:  Temperature ( ^oC) = Vout * (100 ^oC/V)
So if  Vout  is  1V , then, Temperature = 100 ^oC, The output voltage varies linearly with temperature. 

Converting analog to Digital 

However in the weather monitoring system, the signal from LM35DZ will need to be converted to digital so that can be read by Altera. In this project, I used ADC0804 to convert the electrical signal to digital.

 Here is the process to get almost accurate data from ADC0804.

• Connect CS pin, V(-ve) pin, AGND and DGND to ground.
• Give a 0 to WR pin, and then a 1. The low-to-high edge will start data conversion. The high-to-low will eventually set the INTR pin to high.
• Check when the INTR pin goes low. If INTR pin is 0, we're sure that the data is converted.
• Give a 0 to RD pin. Data will be present at the data port of ADC. Read it, and then set RD to 1.

ADC Connection

Measuring temperature using LM35 DZ

LM 35 DZ Sensor

Temperature is an abstract quantity and as such must be defined in terms of the behaviour of materials as the temperature changes. This is accomplished by defining the temperature associated with phase transformations in several different materials over the temperature range from -259 °C to 1084 °C.
This system uses an Integrated Circuit (IC) Temperature Sensor which is the LM35DZ.

Circuit Diagram with ADC

How it works...

The system uses 3 sensor : Temperature sensor, humidity sensor and IR sensor for rainfall measurement.  These 3 sensors will measure the physical quantity and the signal from 3 sensor will be converted to digital signal using ADC 0804. 
End of January 2012, I have finished the hardware part involving 3 sensors and ADC. I'll explain about the hardware part in next post.
By now, I am busy with the software part to do a programming using verilog HDL.

What is this project all about...

ALTERA DE 2 BOARD

This project divided into two parts: hardware and software. Hardware part includes the ALTERA board and three sensors, which converts physical quantities such as temperature, humidity, and rainfall into electrical analogue signal. An Analogue-to-Digital Converters (ADC) circuit is needed in order to convert the physical signal to an electrical signal. After signal conditioning the analog signals are given as input to the eight channels ADC to convert them into digital data. Altera periodically read these data from ADC and display the values of measured quantities on LCD display.
To know ALTERA

For software part, Field-Programmable Gate Array (FPGA) was found to be other alternative integrated circuit apart from microcontroller. Verilog HDL coding is applied to control all the system by reading the output signal from sensor and convert it to get the output (display).

The very basic nature of FPGAs allows it to be more flexible than most microcontrollers. The term field programmable already tells you that the whole FPGA device can be reprogrammed to do any logic task that can be fitted into the number of gates that it has. You can rewire all the logic gates to configure it to the task you had in mind. Microcontrollers already have their own circuitry and instruction set that the programmer must follow in order to write code for that microcontroller which restricts it to certain tasks.

week 1 activity

• on 17th Jan we had first FYP briefing for this semester
• so we only knew that student must have their own blog for fyp. the blog will function as logbook which we previously done for last semester for FYP 1
• in this blog, i will present my progress of project every week
• since this is my first post i have nothing more to write, but for the progress i will upload the circuit diagram for sensor part in next post