SBHS_Shematic Diagram With Description

Single Board Heater SystemSchematic Diagram with description

March 5, 2010

Contents

1 Introduction 21.1 About this Manual . . . . . . . . . . . . . . . . . . . . . . . . 21.2 Single Board Heater System . . . . . . . . . . . . . . . . . . . 2

2 Schematic Diagram and Description 32.1 Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . 32.2 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.3 Microcontroller-ATmega16 . . . . . . . . . . . . . . . . . . . . 52.4 In-System Programmer(ISP) for ATmega16 . . . . . . . . . . 72.5 Temperature Sensor and Instrumentation Amplifier . . . . . . 92.6 Heater and Fan Driver-MOSFET “IRFZ 48N” . . . . . . . . . 112.7 RS-232 serial port to TTL compatible interface . . . . . . . . 122.8 USB to serial UART interface . . . . . . . . . . . . . . . . . . 142.9 LCD Display . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.10 Buzzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

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1 Introduction

1.1 About this Manual

This manual is intended to provide the user with Schematic diagram of ‘Sin-gle Board Heater System’ with its description.

1.2 Single Board Heater System

The set up mimics a process in which temperature is been monitored. Itconsists of an 8-bit microcontroller, display, instrumentation amplifier andassociated circuitry. The process comprises of a heater, fan and a temper-ature sensor. The amount of current passing through the coil decides thetemperature of the thin metal plate. A temperature sensor is used to sensethis temperature. A fan is placed near to the heating mechanism. Amount ofpower delivered to both heater and fan can be controlled by passing a com-mand through serial port via microcontroller.Now, microcontroller generatePWM(Pulse Width Modulation) signal for the MOSFET to deliver desiredamount of power to fan and heater. It could thus be used as a small plantreadily available for various experimentation and study purpose.

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2 Schematic Diagram and Description

2.1 Schematic Diagram

Figure 1: Schematic Diagram of Single Board Heater System

Fig.1 shows the schematic diagram of Single Board Heater System. Itconsist of Power Supply, Microcontroller-ATmega16, Temperature sensor andInstrumentation amplifier, Heater and Fan Driver-MOSFET IRFZ 48N, USBto serial UART interface,RS-232 serial port to TTL compatible interface,LCD display,Buzzer. Explanation of each is given below.

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2.2 Power Supply

We are using +12V, 400W SMPS for providing power to Single Board HeaterSystem. Output of SMPS is connected to X8-1(12V IN) and X8-2(GND) asshown in Fig.2(a). To avoid noise and fluctuation problem 12V power supplyis connected across series combination of diode and 1000µ F capacitor asshown in Fig.2(b). All necessary voltages are derived from this +12V supplyusing low-dropout output voltage regulator IC ‘LM1117’ as shown in Fig.3.Microcontroller ‘ATmega16’ and temperature sensor‘AD590’ require +5Vsupply, which is derived using two separate IC ‘LM1117’ for each. Heaterand fan require +12V supply, hence +12V output of SMPS is directly usefor both.

Figure 2: Power Supply Section

Figure 3: voltage regulator-IC LM1117

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2.3 Microcontroller-ATmega16

Microcontroller ‘ATmega16’ is heart of the Single Board Heater System(SBHS). It work on the +5V power supply. Pins 10(VCC) and 30(AVCC)are connected to +5V power supply. Pins 11 and 31 are grounded.Pin 9 isactive low reset pin. A low level on Reset Input pin for longer than the mini-mum pulse length(50ns) will generate a reset, even if the clock is not running.Shorter pulses are not guaranteed to generate a reset. For generating low levelcombination of resistor and capacitor with push button is used. Reset pinis also connected to pin no.3 of In-System Programmer(ISP). Pin 32(AREF)is the analog reference pin for the A/D converter. It is connected to +5Volts. By varying the voltage on this pin one can vary the reference voltagefor A/D converter. Pin 14 is Receive Data(RXD) and pin 15 is Transmit

Figure 4: Microcontroller-ATmega16

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Data(TXD), used for receiving and transmitting data, respectively. Thesepins are used for sending data to PC and receving data from PC via USBor RS-232, depending on serial communication jumper(J8 and J9) position.If both jumper are connected to pin no.1 and pin no.2 as shown in Fig.4,then RS232 is functioning. If both jumper are connected to pin no.2 and pinno.3 , then USB is functioning. PWM signal for fan, heater and buzzer aregenerated by Microcontroller at pin 18, pin 19 and pin 21, respectively.Fig.5 shows crystal oscillator connections to Microcontroller. 8MHz crystal

Figure 5: Crystal Oscillator Connections

is connected across pin no.12 and pin no.13. C1 and C2 should always beequal. Value of capacitor is 22pF.

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2.4 In-System Programmer(ISP) for ATmega16

Programming of the Single Board Heater System(SBHS) is done throughIn-System Programming (ISP). One can use available ISP programmer forprogramming Microcontroller ‘ATmeg16’. One technique is use of pc’s paral-lel port. The program is loaded into the SBHS using the parallel port of PC.A programmer software like ‘ICCV AVR’is required to write and downloadprogram from PC to AVR’s flash memory. MOSI(Pin 15), MISO(pin 16),SCK(pin 17) and RESET(pin 29) are required for programming ATmega16.

Figure 6: ISP Module

Fig.7 shows circuit diagram of ISP Programmer. It consist of IC 74LS244DW,parallel-port and 10 pin FRC mail connector. IC 74LS244DW is used forbuffering purpose. To identify dongle, Pin 2 to pin 12 and pin 3 to pin pin 11of parallel port are short circuited. The PCs parallel-port pins 4 and 5 drivebuffer IC 74LS244DW by enabling its pins 19 and 1, respectively. A logiczero on these pins will allow the passing of the serial clock and data duringprogramming. MISO, MOSI, SCK and RESET pins are buffered using IC74LS244DW. Reset pin must be held low while programming microcontrollerATmega16. SCK pin carry serial clock generated by the programmer fromthe PC.

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Figure 7: Circuit Diagram of ISP Programmer

Figure 8: 10 Pin Connector Port for ATmega16 ISP

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2.5 Temperature Sensor and Instrumentation Ampli-fier

Figure 9: Bottom View of Temperature Sensor ‘AD590’

Temperature sensor AD590 is three pins IC. Fig.9 shows bottom viewof temperature sensor AD590. Vcc pin is connected to +5V power supply.Sensor output is collected at pin mark as ‘SEN ’. The signal generated by

Figure 10: Instrumentation Amplifier

temperature sensor AD590 is in µA/°K. It is converted to mV/°K by takingit across a 1KWresistor. A 1KWresistor is derived using 330W resistor and10KWpot. The °K to°C conversion is done by subtracting 272mV from thevoltage generated across this 1KW. 272mV is derived by using potential di-vider network. Potential divider network consist of 4.7KWresistor is in series

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with 10KWpot. 5V power supply is applied across this network. By adjustingpot one can exactly derived 272mV.Now one input of the Instrumentation Amplifier is fed with the mV/°K read-ing derived using sensor output and the other with 272mV. The resultingoutput is now in mV/°C. The output of the Instrumentation amplifier is fedto microcontroller for further processing.Fig.10 shows operational amplifier IC ‘LM324’configured as Instrumenta-tion Amplifier. IC ‘LM324’is quadruple operational amplifiers, three(19A,19B, 19C) out of four amplifiers is configured as unity gain buffer amplifier.Buffer amplifier provied high input impedance to sensor output and low out-put impedance. Remaining one operational amplifier(19D) is configured assubtractor, which actually subtract two signals.

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2.6 Heater and Fan Driver-MOSFET “IRFZ 48N”

Figure 11: MOSFET -IRFZ48NFig.11 shows front view of MOSFET “IRFZ 48N”. Pin 19(PD5) of

ATmega16 deliver PWM signal for heater. This signal is connected to thegate of MOSFET and also grounded through LED and 1KΩ for indicationpurpose. Fig.12 shows different connections to the heater MOSFET. Drainof MOSFET is connected to the one end of heater coil, other end of heater

coil is connected to +12v power Supply. Source pin is grounded.

Figure 12: Heater MOSFET

Pin 18(PD4) of ATmega16 deliver PWM signal for fan. This signal isconnected to the gate of MOSFET and also grounded through LED and1KΩ for indication purpose. Fig.12 shows connections to the fan MOSFET.12V DC fan is used in the SBHS, hence drain of MOSFET is connected tothe negative terminal of fan , other terminal of fan is connected to +12vpower Supply. Source pin is grounded.

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Figure 13: Fan MOSFET

2.7 RS-232 serial port to TTL compatible interface

Figure 14: MAX202 Pin Configuration

The MAX202 is an integrated circuit that converts signals from an RS-232 serial port to signals suitable for use in TTL compatible digital logiccircuits. The MAX232 is a dual driver/receiver.Serial RS-232 communication works with voltages (between -15V to -3V usedto transmit a binary ‘1’and +3V to +15V to transmit a binary ‘0’) whichare not compatible with today’s computer logic voltages. On the other hand,classic TTL computer logic operates between 0V to +5V (roughly 0V to+0.8V referred to as low for binary ‘0’, +2V to +5V for high binary ‘1’).Modern low-power logic operates in the range of 0V to +3.3V or even lower.So, the maximum RS-232 signal levels are far too high for today’s computerlogic electronics. Therefore, to receive serial data from an RS-232 interfacethe voltage has to be reduced, and the 0 and 1 voltage levels inverted. Inthe other direction (sending data from some logic over RS-232) the low logic

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voltage has to be“bumped up”, and a negative voltage has to be generated,too.

Figure 15: MAX202 Typical Operating Circuit

Figure 16: Schematic of MAX202 with RS-232 Connector

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2.8 USB to serial UART interface

The FT232R is a USB to serial UART interface with data transfer at TTLlevels.Fig.17 shows connection of IC ‘FT232R’ with USB , ATmega16 and othercircuitry.Power supply is derived from Pin 1 of USB, which is connected to the pins4 and 20 of IC ‘FT232R’. Decoupling capacitors are used between Vcc andground. Pins 2 and 3 of USB are connected to pins 16 and 15 through 27Ωresistor, respectively. Pin 16 is USB Data Signal Minus (USBDM) and pin15 is USB Data Signal Plus(USBDP). Pin 4 of USB is grounded. Pin 1 isTransmit Asynchronous Data Output(TXD) which is connected to RXD(pin14 of ATmega16 ) via jumper J9 and Pin 5 is Receiving Asynchronous DataInput(RXD) which is connected to TXD(Pin 15 of ATmega16) via jumperJ8. Pin 22 Configurable CBUS I/O Pin. Function of this pin is configuredin the device internal EEPROM. Factory default configuration is RXLED(Receive data LED drive). It pulses low when receiving data via USB. Pin 23Configurable CBUS I/O Pin. Function of this pin is configured in the deviceinternal EEPROM. Factory default configuration is TXLED (Transmit dataLED drive). It pulses low when transmitting data via USB . We are usingboth pins in factory default configuration i.e. for indication purpose, henceboth pins are grounded through LED and 270Ω separately.

Figure 17: FT232RL

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2.9 LCD Display

LCD display JHD162A is use for display. Display Content 16 CHAR x2ROW. Each character consist of 5 x 8 dots. It has 16 pins. LED back-light is provided,which makes seeing the chracters on screen easier. Fig.18

Figure 18: Pin Configuration

shows pin configuration of LCD display ‘JHD162A’. Pin 1 and 2 are thepower supply pins.+5V is supplied on pin no.2(Vcc), pin 1(Vss) is grounded.Pin 3 is the contrast setting pin. It’s connected to variable point of poten-tiometer, remaining two point of potentiometer are connected between Vccand ground. By adjusting potentiometer one can adjust contrast of LCDdisplay. Pins 4 , 5 and 6 are control pins of the LCD. Pin 4 is RS(register se-lect) pin. Depending on logic level of RS pin LCD work in Instruction modeor Character Mode. If RS pin is high then data on data pin(DB0-DB7) istreated as instruction. If RS pin is low then data on data pin(DB0-DB7)is treated as character. Pin 5 is R/W(Read/Write) pin. Here LCD is usefor displaying purpose only, hence R/W pin is always set to logic ‘0’. Pin6 is E(Enable) pin it simply work as clock signal to the LCD. Falling edgeon this pin processed data present on the data pin. Pin 7 to 14 are datapins. Pin 15 and pin 16 are internally connected to the LED, current limit-ing resister(100Ω) is connected externally in series. Port ‘C’of ATmega16 isused for LCD display.

Figure 19: LCD Display

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2.10 Buzzer

Figure 20: Buzzer

Buzzer is used for indication purpose. One can use buzzer while debug-ging the program or for indication like ON/OFF condition of SBHS.Buzzre is connected between +12V system power supply and collector oftransistor BC548. Emitter of transistor ‘BC548’ is grounded. PD7(pin no.21of ATmega16) generate signal for buzzer. PD7 is connected to the baseof transistor ‘BC548’ through voltage divider consist of 22KΩ and 100KΩresistor.

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