assembling ckt boards

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    Chapter 4Assembling the circuit Boards

    Stage 1:

    Assemble the white line sensor

    Stage 2:

    Assemble the main board

    Stage 3:

    Assemble the Linear infrared range finder

    Stage 1:White line sensor assembling

    Important instructions:First understand the circuit diagram. Read the instructions first.

    If you dont know the component then read the component data sheet first.Trace the PCB first then place the components. Once the component is soldered it is very

    difficult to remove it again.

    Circuit diagram

    Figure 4.1 Circuit diagram of the white line sensor

    White line sensors works on 9V supply. LED (D12) is a high power ultra brightRed LED. Its light intensity can be controlled by varying the variable resistor R38. A

    330E resistor is inserted in series to protect the Red LED from current surge. This resistor

    will maintain current in safer limit even if value of the potentiometer becomes zero.

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    For the white line sensing photo transistor KL3B from ST microelectronics is

    used. Collector current is limited by a 47K ohm resistor R37. When photo transistor is

    saturated because of reflected red light maximum collector current will be approx 190micro ampere. To avoid effect of loading a unity gain operational amplifier is used as a

    buffer. There are seven white line sensors on the PCB. This analog signal is then

    connected through 16 pin FRC connector and FRC cable to the main board.

    Figure 4.2 Front side and the back side of the white line sensor board

    Figure 4.3 Pin polarity of the LED and Photo transistor

    Figure 4.4 Resister colure code

    Colure code for 330 ohm resister is Orange, Orange, Brown, and GoldColure code for 47 K ohm resistor is Yellow, Purple, Orange, and Gold

    Figure 4.5 Variable resistor and 16 pin FRC connector

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    Figure 5.6 Correct component placements on the sensor side

    Figure 5.7 Correct component placements on the connector side

    PCB assembling steps:

    1. Mount all the photo transistors on the board. Be careful about collector andemitter placement.

    2. Mount all the 4 pin LED on the PCB. Be careful about anode and cathodeplacement.

    3. Solder 330 ohms and 47 K ohms resistor on the sensor side.4. Solder the 14 pin IC holder on the connector side. Notch of the IC holder must be

    pointing towards left side as shown in fig 5.7

    5. Solder the Blue colored variable resistor on the PCB

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    6. Mount the 16 pin FRC connector on the PCB7. Mount IC LM324 in the IC holder. Make sure that notch on the IC matches with

    the notch on the IC holder.

    Mount all the components with correct polarity.

    Solder all the components by the above sequence only. If you mount larger

    component first then it will be difficult to mount the smaller components.While soldering hold the component with your hand then touch the soldering

    irons tip to the component and touch the solder wire on the tip. If you follow

    this procedure then you will get the best finishing in the soldering.

    Do not touch the soldering irons tip for more than 5 seconds to any of the

    component

    Fitting the White line sensor board on the robot

    Figure 5.8 Nut and bolt fitting for mounting of the white line sensor board

    1. CASE 2: Add five 3/16 size nuts (Marked by number 17 in fig. 3.4 and 3.5) on theprefixed 5/32 1.25 inch bolts

    2. CASE 1: Insert the 1.25 inch counter sink 6 number screw (Marked by number 18in fig. 3.4 and 3.5) then add five 3/16 size nuts (Marked by number 17 in fig. 3.4

    and 3.5)

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    Figure 5.9 White line board mounting

    As shown in fig 5.9 fit the board using 0.5 inch 5/32 counter sink bolts (Marked by

    number 17 in fig. 3.4 and 3.5) for the case 2. For the case 1 screw will directly fit in

    the hole.

    Do not apply high torque on the nuts. It can damage the white line sensor

    board

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    Stage 2:

    Assembling the main board

    Step 1:

    Figure 5.10 Top and bottom side of the main board

    Fit 0.75 inch 5/32 counter sink bolts (Marked by number 15 in fig. 3.4 and 3.5) and fit

    them with three 5/32 nuts (Marked by number 21 in fig. 3.4 and 3.5)

    Fit the nuts at the bottom side. Do not apply excessive torque while tightening.

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    Step 2:

    Connector placements

    Figure 5.11 Connector placements at the back side of the main board

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    Step 3:

    Power management section and the RS232 communication module

    Figure 5.12 Power management section

    CON2 is 10 pin FRC connector. It is used for the charging the onboard battery.

    D27 is used for the reverse polarity protection. D26 is a red colored LED which indicatescharging of the battery. S2 is double pole double throw (DPDT) switch. In one setting it

    provides supply to the robot. In other setting it allows battery to be charge. On and off

    positions are shown in the Fig 5.14. This is done so that one can either switch on therobot or charge it but user can not do both the things at the same time which can damage

    robot or the battery or in worse case both. Battery is connected to the SL1 which is 10 pin

    Relaymate connector. Four wires are connected for the redundancy. D29 is used to

    restrict the flow of current from battery to the circuit only. Capacitor C4 is used like atemporary battery which can act as secondary battery for few tens of milliseconds. This is

    done to protect microcontroller and other circuit from surge current due to motors when

    battery is almost discharged. IC 7805 (IC7) and IC 7809 (IC8) are 5 Volts and 9 Voltsvoltage regulators respectively. 0.1 uF capacitors (C5 and C6) are connected between V

    out and ground for improved ripple rejection. Both of the voltage regulators are

    connected to the heat sink for dissipating the heat.

    Figure 5.13 TTL to RS232 conversion

    MAX232 (IC2) is used for converting TTL levels in to the RS232 level for the serial

    communication with the PC. Capacitors C8 to C11 are used for the boosting the voltage

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    levels to the RS232 levels. For the RS232 communication a DB9 PCB mountable female

    connector (X1) is used.

    Figure 4.14 Components placements for the power management and

    serial communication

    1. It is very important that you mount the switch first. Do not push the leads of theswitch through PCB. Just keep the switch on the PCB and solder it.

    2. Mount the 10 pin FRC connector and then voltage sensing resistors R58 and R59.3. Mount smaller components first then go for larger components.4. Watch out for the LED, diode and capacitor polarity and notch on the connector.5. For the 9 volts regulator you have to use the white LED which has transparent

    colored casing and yellowish white colure inside.

    6. Mount the voltage regulator IC7805 and IC7809 on the heat sink first by thescrew fitted on the heat sink. Do not forget to mount the heat sink on the main

    board by the screws.7. Solder the voltage regulators only after the proper mounting.8. Do not interchange the positions of the IC7805 and the IC7809

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    Step4:

    Motor controller placement

    Figure 4.15 H Bridge driver for the motor control

    The LMD18200 is a 3A H-Bridge designed for motion control applications. The

    device is built using a multi-technology process which combines bipolar and CMOScontrol circuitry with DMOS power devices on the same monolithic structure. It is idealfor driving DC and stepper motors. The LMD18200 accommodates peak output currents

    up to 6A.

    Figure 4.16 Pin layout of the LMD18200 H bridge

    C13 to C16 are the 0.01uF capacitors used for the bootstrap. Using these capacitors HBridge generates voltage higher than Vcc to drive its upper side MOSFETs. Output is

    connected to the motors through 4 pin Relaymate connectors (CON2 and CON3). Pulse

    width modulated signal is fed to the motor controllers from the output compare pins from

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    the microcontroller. Direction and brake inputs are given from the port B of the

    microcontroller. LEDs D2 to D7 indicates direction, Brake and the PWM commands

    from the microcontroller. LEDs D8 to D11 are in the form of the arrows which showsmotor direction. Resistors R14 and R15 are used for the current sensing.

    Table 4.1 Logical truth table

    4.17 Components placements for motor controller

    Arrow indicator and its 330 Ohm resistor will be fitted in step 5.

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    Step 5:

    Wireless infrared communication and jumper settings

    Figure 4.18 Wireless infrared communication and jumper settingsCON1 is 10x2 female BERG stripe used as expansion slot for the wireless

    communication. JP2 is the modified male BERG connector used for the communication

    mode selection. IC TSOP1738 is used for the infrared communication. R^ and the C12 isused for the noise decoupling. R% is the pull up resistor. Not gate IC3C is used to drive

    the LED which blinks when valid infrared communication is established.

    Pin 1, 2: Receive data (RXD)

    Pin 3, 4: Transmit data (TXD)Pin 5, 6: 5V

    Pin 7, 8: Ground

    Pin 9, 10: 9VPin 11 to 20: No connection

    Figure 4.19 Expansion slot for the wireless communication

    Pin 1, 2: Wireless infrared communication

    Pin 3 to 8: No connectionPin 9, 10: RS232 receive

    Pin 11, 12: RS232 transmit

    Figure 4.20 Jumper setting for the communication mode selection

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    Figure 4.21 Wireless infrared communication and jumper settings

    Do not remove cap placed at the bottom of the IC TSOP1738. It is used to avoid

    contact between the IC and the PCB tracks.Mount IC holder, LED and the capacitor with correct polarity.

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    Step 6:

    Microcontroller and some audio visual indicators

    Figure 4.22 Microcontroller and some audio visual indicators

    VCC, AVCC and AREF are connected to the 5V and GND and AGND are

    grounded. Capacitors C1 and C2 are used with 4MHz crystal Q1 to generate clock forthe microcontroller. Resistor and the capacitor R4 and C3 forms the RC network for

    providing power on reset. MISO, MOSI, SCK, negative RESET and ground pins are

    also connected to the In System Programming (ISP) port. Analog data from linearinfrared range finder is given to the ADC0 to ADC3 of the microcontroller. Pins PB0

    to PB3 of the microcontroller are connected to the Left and Right motor controllers.LEDs D3 to D6 are used to indicate status of these pins. Pulse width modulated

    signals for the left and the right motors are supplied from the OC1A and OC1B of the

    microcontroller. LEDs D2 and D7 are used as visual indicator for the PWM signalout. Self test switch is connected to the interrupt 0 of the microcontroller. Resistors

    R58 and R59 forms the voltage divider network which is reduces the voltage level

    below 5V. This level is sensed by the ADC6 of the microcontroller. Pin PB4 of the

    microcontroller is used to drive the Buzzer.

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    Figure 4.23 Microcontroller and some audio visual indicators component

    placements

    Mount the LEDs, transistor and the buzzer with the correct polarity

    Mount the connector and IC holder with its notch facing left.Do not forget to solder C1 and C2 which are inside of the IC holder.

    SELF TEST switch has to be soldered like SMD component.

    Solder the 330 ohm resistor for the arrow indicator from the step 5Mount the arrow indicator on the top of it. (Call the TAs before mounting the

    arrow indicator.

    Figure 4.24 Fitting of the arrow indicator

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    Step 7:

    White line sensor circuits

    Figure 4.25 Signal conditioning circuit of the white line sensors

    CON4 is 2*8 pin right angled mane BERG connector which is fitted at the bottom

    side of the board. When there is no white line in front of the white line sensor it givesapproximately 7 volts. When sensors are exposed to the white line photo transistor goes

    in to saturation and output drops to the approximately to the 0.27 volts. D13 to D19 are

    3.3 volt Zener diodes these diodes are used to distinguish between presence and absenceof the white. R66 to R72 are the current limiting resistors which limits the base current to

    the transistors T2 to T8. Resistors R2, R19, R21, R23, R25, R27, and R29 are the bias

    stabilization resistors. R1, R3, R20, R22, R24, R26, R28 are the collector resistors.Transistors T2 to T8 are used to convert analog voltage of white line sensors (0.22V to

    7.8V) to the digital value of 0 to 5 volts. IC74245 (IC4) is used to drive bar graph LED

    display. LEDs from the bar graph display glows if white line sensors find the white line.

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    Figure 4.26 White line signal conditioning and the expansion slot component

    placement

    Mount the Zener diode correctly.