monitering section of Micro C/OS-II kernel in ARM powered microcontroller

6.3. Monitoring Section

6.3.1. Temperature Sensor

         The LM35 does not require any external calibration or trimming to provide typical accuracies of at room temperature and °C over a full -55 to +150°C temperature range. Low cost is assured by trimming and calibration at the wafer level [6]. The LM35’s low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus supplies.

Features 

Calibrated directly in ° Celsius (Centigrade)

Linear + 10.0 mV/°C scale factor

 

Fig 6.3: Temperature Sensor

0.5°C accuracy guarantee able (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 ±¼°C typical

Low impedance output, 0.1 Ohm for 1 mA load

         As it draws only 60 µA from its supply, it has very low self-heating, less than 0.1°C in still air [6]. The LM35 is rated to operate over a -55° to +150°C temperature range, while the LM35C is rated for a -40° to +110°C range (-10° with improved accuracy).

 

Fig 6.4: Basic Centigrade Temperature Sensor

The LM35 series is available pack. Aged in hermetic TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available in the LM35 series are precision integrated-circuit temperature plastic TO-92 transistor package. The LM35D is also avail- sensors, whose output voltage is linearly proportional to the table in an 8-lead surface mount small outline package and a Celsius (Centigrade) temperature. The LM35 thus has a plastic TO-220 package.

6.3.2. GLCD

This paper and project outline the design of a graphical LCD driver for the Crystalfontz CFAG12864B series (128 x 64 pixel) graphical display which can be easily modified to drive any Samsung KS0108 based graphical LCD.

Design and Implementation

The CFAG12864B

The CFAG12864B is a 128 x 64 pixel graphical LCD with backlight. It is driven by 2 64 x 64 pixel Samsung KS0108 drivers. Figure 1 shows an image of what the LCD looks like with a sample output of a tractor. The actual view area of the LCD is 60 mm x 32.6 mm [6].

Fig 6.6: the CFAG12864B graphical Liquid Crystal Display

Pin Assignments

Setting up the LCD and turning it on

The Appendix contains a detail pin-out of the LCD but the important pins for this section are as follows:

 

Table 6.3: GLCD Pin Assignments 

In order for the LCD to power up, Pin 1 must be connected to + 5V, Pin 2 must be connected to GND and Pin 3 & Pin 18 must be connected as illustrated in Fig. 2. Adjusting this value adjusts the contrast but the Pins must be connected in this way in order for the image to be seen on the screen (if it isn’t there is essentially no contrast and nothing will be displayed [6].

Fig 6.7: LCD pins connection

6.2.3 LED: (light emitting diode)

          When a light-emitting diode is forward biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is often small in area (less than 1 mm²), and integrated optical components may be used to shape its radiation pattern.

          LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output. Light-emitting diodes are used in applications as diverse as replacements for aviation lighting, automotive lighting (particularly brake lamps, turn signals and indicators) as well as in traffic signals[6].

 

 Fig 6.8: Structure of LED

 6.2.4. MAX 232

Introduction:

MAX-232 is primary used for people building electronics with an RS-232 interface [6]. Serial RS-232 communication works with voltages (-15V ... -3V for high) and +3V ... +15V for low) which are not compatible with normal computer logic voltages. To receive serial data from an RS-232 interface the voltage has to be reduced, and the low and high voltage level inverted. In the other direction (sending data from some logic over RS-232) the low logic voltage has to be "bumped up", and a negative voltage has to be generated, too. In telecommunications, RS-232 is a standard for serial binary data interconnection between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating Equipment).

Fig 6.9: Pin Diagram of Max 232

RS232

Fig 6.10: RS232 DB 9 Male Pin Out
Devices which use serial cables for their communication are split into two categories. These are DCE (Data Communications Equipment) and DTE (Data Terminal Equipment.) Data Communications Equipment is devices such as your modem, TA adapter, plotter etc while Data Terminal Equipment is your Computer or Terminal.