Single Board Heater System
Schematic Diagram with description
March 5, 2010
Contents
1 Introduction
1.1 About this Manual . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Single Board Heater System . . . . . . . . . . . . . . . . . . .
2 Schematic Diagram and Description
2.1 Schematic Diagram . . . . . . . . . . . . . . . . .
2.2 Power Supply . . . . . . . . . . . . . . . . . . . . .
2.3 Microcontroller-ATmega16 . . . . . . . . . . . . . .
2.4 In-System Programmer(ISP) for ATmega16 . . . .
2.5 Temperature Sensor and Instrumentation Amplifier
2.6 Heater and Fan Driver-MOSFET “IRFZ 48N” . . .
2.7 RS-232 serial port to TTL compatible interface . .
2.8 USB to serial UART interface . . . . . . . . . . . .
2.9 LCD Display . . . . . . . . . . . . . . . . . . . . .
2.10 Buzzer . . . . . . . . . . . . . . . . . . . . . . . . .
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1
1.1
Introduction
About this Manual
This manual is intended to provide the user with Schematic diagram of ‘Single Board Heater System’ with its description.
1.2
Single Board Heater System
The set up mimics a process in which temperature is been monitored. It
consists of an 8-bit microcontroller, display, instrumentation amplifier and
associated circuitry. The process comprises of a heater, fan and a temperature sensor. The amount of current passing through the coil decides the
temperature of the thin metal plate. A temperature sensor is used to sense
this temperature. A fan is placed near to the heating mechanism. Amount of
power delivered to both heater and fan can be controlled by passing a command through serial port via microcontroller.Now, microcontroller generate
PWM(Pulse Width Modulation) signal for the MOSFET to deliver desired
amount of power to fan and heater. It could thus be used as a small plant
readily available for various experimentation and study purpose.
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2.1
Schematic Diagram and Description
Schematic Diagram
Figure 1: Schematic Diagram of Single Board Heater System
Fig.1 shows the schematic diagram of Single Board Heater System. It
consist of Power Supply, Microcontroller-ATmega16, Temperature sensor and
Instrumentation amplifier, Heater and Fan Driver-MOSFET IRFZ 48N, USB
to 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 Heater
System. Output of SMPS is connected to X8-1(12V IN) and X8-2(GND) as
shown in Fig.2(a). To avoid noise and fluctuation problem 12V power supply
is connected across series combination of diode and 1000µ F capacitor as
shown in Fig.2(b). All necessary voltages are derived from this +12V supply
using low-dropout output voltage regulator IC ‘LM1117’ as shown in Fig.3.
Microcontroller ‘ATmega16’ and temperature sensor‘AD590’ require +5V
supply, which is derived using two separate IC ‘LM1117’ for each. Heater
and fan require +12V supply, hence +12V output of SMPS is directly use
for 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 is
active low reset pin. A low level on Reset Input pin for longer than the minimum 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 level
combination of resistor and capacitor with push button is used. Reset pin
is 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 +5
Volts. By varying the voltage on this pin one can vary the reference voltage
for 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. These
pins are used for sending data to PC and receving data from PC via USB
or 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 pin
no.3 , then USB is functioning. PWM signal for fan, heater and buzzer are
generated 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 be
equal. 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 through
In-System Programming (ISP). One can use available ISP programmer for
programming Microcontroller ‘ATmeg16’. One technique is use of pc’s parallel 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 download
program 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 for
buffering purpose. To identify dongle, Pin 2 to pin 12 and pin 3 to pin pin 11
of parallel port are short circuited. The PCs parallel-port pins 4 and 5 drive
buffer IC 74LS244DW by enabling its pins 19 and 1, respectively. A logic
zero on these pins will allow the passing of the serial clock and data during
programming. MISO, MOSI, SCK and RESET pins are buffered using IC
74LS244DW. Reset pin must be held low while programming microcontroller
ATmega16. SCK pin carry serial clock generated by the programmer from
the 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 Amplifier
Figure 9: Bottom View of Temperature Sensor ‘AD590’
Temperature sensor AD590 is three pins IC. Fig.9 shows bottom view
of 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 taking
it across a 1KWresistor. A 1KWresistor is derived using 330W resistor and
10KWpot. The °K to°C conversion is done by subtracting 272mV from the
voltage generated across this 1KW. 272mV is derived by using potential divider 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 adjusting
pot one can exactly derived 272mV.
Now one input of the Instrumentation Amplifier is fed with the mV/°K reading derived using sensor output and the other with 272mV. The resulting
output is now in mV/°C. The output of the Instrumentation amplifier is fed
to microcontroller for further processing.
Fig.10 shows operational amplifier IC ‘LM324’configured as Instrumentation 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 output impedance. Remaining one operational amplifier(19D) is configured as
subtractor, which actually subtract two signals.
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2.6
Heater and Fan Driver-MOSFET “IRFZ 48N”
Figure 11: MOSFET -IRFZ48N
Fig.11 shows front view of MOSFET “IRFZ 48N”. Pin 19(PD5) of
ATmega16 deliver PWM signal for heater. This signal is connected to the
gate of MOSFET and also grounded through LED and 1KΩ for indication
purpose. Fig.12 shows different connections to the heater MOSFET. Drain
of 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 is
connected to the gate of MOSFET and also grounded through LED and
1KΩ 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 to
the negative terminal of fan , other terminal of fan is connected to +12v
power 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 RS232 serial port to signals suitable for use in TTL compatible digital logic
circuits. The MAX232 is a dual driver/receiver.
Serial RS-232 communication works with voltages (between -15V to -3V used
to transmit a binary ‘1’and +3V to +15V to transmit a binary ‘0’) which
are 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 computer
logic electronics. Therefore, to receive serial data from an RS-232 interface
the voltage has to be reduced, and the 0 and 1 voltage levels inverted. In
the 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 TTL
levels.
Fig.17 shows connection of IC ‘FT232R’ with USB , ATmega16 and other
circuitry.
Power supply is derived from Pin 1 of USB, which is connected to the pins
4 and 20 of IC ‘FT232R’. Decoupling capacitors are used between Vcc and
ground. Pins 2 and 3 of USB are connected to pins 16 and 15 through 27Ω
resistor, respectively. Pin 16 is USB Data Signal Minus (USBDM) and pin
15 is USB Data Signal Plus(USBDP). Pin 4 of USB is grounded. Pin 1 is
Transmit Asynchronous Data Output(TXD) which is connected to RXD(pin
14 of ATmega16 ) via jumper J9 and Pin 5 is Receiving Asynchronous Data
Input(RXD) which is connected to TXD(Pin 15 of ATmega16) via jumper
J8. Pin 22 Configurable CBUS I/O Pin. Function of this pin is configured
in the device internal EEPROM. Factory default configuration is RXLED
(Receive data LED drive). It pulses low when receiving data via USB. Pin 23
Configurable CBUS I/O Pin. Function of this pin is configured in the device
internal EEPROM. Factory default configuration is TXLED (Transmit data
LED drive). It pulses low when transmitting data via USB . We are using
both pins in factory default configuration i.e. for indication purpose, hence
both 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 x
2ROW. Each character consist of 5 x 8 dots. It has 16 pins. LED backlight 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 the
power 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 potentiometer, remaining two point of potentiometer are connected between Vcc
and ground. By adjusting potentiometer one can adjust contrast of LCD
display. Pins 4 , 5 and 6 are control pins of the LCD. Pin 4 is RS(register select) pin. Depending on logic level of RS pin LCD work in Instruction mode
or Character Mode. If RS pin is high then data on data pin(DB0-DB7) is
treated 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 use
for displaying purpose only, hence R/W pin is always set to logic ‘0’. Pin
6 is E(Enable) pin it simply work as clock signal to the LCD. Falling edge
on this pin processed data present on the data pin. Pin 7 to 14 are data
pins. Pin 15 and pin 16 are internally connected to the LED, current limiting resister(100Ω) is connected externally in series. Port ‘C’of ATmega16 is
used 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 debugging the program or for indication like ON/OFF condition of SBHS.
Buzzre is connected between +12V system power supply and collector of
transistor BC548. Emitter of transistor ‘BC548’ is grounded. PD7(pin no.21
of ATmega16) generate signal for buzzer. PD7 is connected to the base
of transistor ‘BC548’ through voltage divider consist of 22KΩ and 100KΩ
resistor.
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