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Incorporating Computer Control into Student Project Work using a PIC Microcontroller

Incorporating Computer Control into Student Project Work using a PIC Microcontroller. Building the PIC Control Board. CONTENTS Printed Circuit Boards (PCBs) Required PIC Board Components Populating the PIC Control Board Soldering Technique Testing Troubleshooting Hardware.

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Incorporating Computer Control into Student Project Work using a PIC Microcontroller

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  1. Incorporating Computer Control into Student Project Work using a PIC Microcontroller

  2. Building the PIC Control Board

  3. CONTENTS Printed Circuit Boards (PCBs) Required PIC Board Components Populating the PIC Control Board Soldering Technique Testing Troubleshooting Hardware

  4. 1. Printed Circuit Boards (PCBs)

  5. A printed circuit board also known as a PCB is a way of manufacturing electronic circuits. A PCB is made from insulating plastic with copper tracks connecting the holes where components are placed. Courtesy of www.technologystudent.com They are designed specially for each circuit and make construction very easy.

  6. PC Graphics Card • PCBs are frequently used as a ‘Black Box’ technology in that they are replaced completely in the event of a malfunction rather than attempting to isolate the specific component that is causing the problem.

  7. 2. Required PIC Board Components

  8. Details of component suppliers for the PCB we are using are available in the Excel file: Student PIC Project Board Components.xls

  9. Details of the PCB we are using are available in the Excel file: Student PIC Project Board Components.xls

  10. 3. Populating the PIC Control Board

  11. PCB Population Method Start with the smaller components e.g. resistors and diodes. Move on to larger components like the IC socket. Finish surface mount with the tall components i.e. capacitors and transistors. Complete the population by connecting the components on flying leads; power socket, USB and reset switch. Do not connect the chip until the board has been tested for power connection.

  12. Start now with the smaller components e.g. resistors and diodes. Ensure correct alignment of diodes

  13. Keep notch to the LHS Move on to larger components like the IC socket.

  14. Q1 Q2 TB1 TB2 C4 TB3 TB6 C1 TB4 TB5 IC1 IC4 C2 C3 Insert taller components; capacitors (C1-C4) , transistors (Q1&Q2), voltage regulators (IC1&IC4) and terminal blocks (TB1 – TB4).

  15. CN1: 2.1mm PCB DC Power Socket PP3 Battery Clip Insert power socket CN1 and connect the PP3 battery clip as shown. This allows the board be powered from either the PSU or 4 x 1.5V AA batteries. NOTE:The red PP3 cable could be connected through a SPST switch to create a master on/off control

  16. If the project under construction requires the use of a 9V external PSU then it is recommended to use an external power socket such as the one shown above. These can be fitted into 3mm acrylic sheet. 2.1mm Power Socket

  17. Complete the population by connecting the components on flying leads; beginning with the reset switch SW1 as shown. It is possible to use 2 cables to connect the reset switch to the PCB by using 2 loops on the board. However, the holes maybetoo small to allow this. SW1 – Reset Switch

  18. For use in a project it will be necessary to mount the USB socket on a flying lead as shown. The black and red cables may be connected in the holes A and B if desired, as they are linked by copper trace. B A CN2: USB 3.5 mm Stereo Socket

  19. Q7 Q5 Q6 Q2 Q3 Q4 Solderless LED holders are available from some suppliers fitted with 200mm leads that retain the LED using a patented clamping device. LED outputs may be connected to outputs Q2 to Q7 using flying leads so that they can be fitted into a project where necessary.

  20. They are very useful for ensuring that students do not short out the LED legs. It is cheaper to connect LEDs by soldering ordinary cable. Plastic LED leg spacers shown are available from some suppliers.

  21. On the student project board at the position for outputs Q0 and Q1 there are terminal blocks so that outputs such as bulbs and motors can be attached. These outputs require a larger current than is available directly from the PIC. Q1 Q0 To overcome this a transistor is used with its base attached to the PIC. The small current from the PIC is used to switch on the transistor allowing a large current to enter the collector. This makes it possible to use outputs like bulbs and motors.

  22. For the purposes of this course we will use a small speaker in output Q0 and a motor in output Q1 as shown above. Q0 Q1 NOTE: Some DC motors can cause the PIC to malfunction due to electromagnetic interference or ‘noise’. To counteract this, fit a 220nF capacitor directly across the motor connections or use a solar type motor.

  23. We are using the following inputs: D6: Micro-switch D7: Push Switch PTM D0/A0: NTC Thermistor 20K D1/A1: NORPS12 LDR NOTE: The 20K thermistor is being used instead of a digital temperature sensor that is difficult to source and expensive. Another terminal block may also be added to allow easier connection.

  24. 4. Soldering Technique

  25. Good soldering is necessary to ensure proper functioning of the PCB. If possible, always use a temperature controlled soldering iron.Click on the screen to activate a short video clip on soldering technique courtesy of Youtube.

  26. Common soldering mistakes.... Too much solder

  27. Too little solder

  28. Unless joints with too little solder are corrected they can eventually crack causing intermittent connection problems. These can be very difficult to diagnose.

  29. ‘Cold’ soldered joint – caused by incorrect technique

  30. Course participants are encouraged to practice their soldering technique if necessary before commencing.

  31. 4. Testing

  32. Do not insert IC until power supply has been tested Your completed PIC board should be tested to establish correct power supply is present on the board and at the IC (5V) before inserting the chip. NOTE: Never solder the board with the IC inserted.

  33. When you measure across pins 5 and 14 in the IC holder you should read approx 5V. If not then refer to the slides on Troubleshooting Hardware. +5 V PIN 18 PIN 1 0V Otherwise, you are ready to insert the IC and begin using the GENIE Design Studio software.

  34. 4. Troubleshooting Hardware

  35. If you do not read approx 5V across pins 5 and 14 on your IC then follow these steps: • Check your power source is working properly i.e. Check your batteries or your PSU. • Carry out a visual check of components to ensure: • Components are inserted in the correct location e.g. resistors and diodes. • Components are inserted with correct polarity i.e. diodes, electrolytic capacitors, transistors. • Components on flying leads are connected properly, particularly the external power socket if used.

  36. If you still have not identified a problem then continue with the following checks: Check whether there is supply voltage (6 or 9V depending on batteries or PSU) and whether the voltage regulator has reduced this to 5V for use with the PIC as shown. 6-9V 0V 5V

  37. If the problem still persists then it is probably due to a physical malfunction such as a poorly soldered joint or a break or crack in the copper trace. To identify this type of problem: Carry out a visual check of all soldered joints and copper traces using a suitable magnifying glass. Check continuity between each component using the multimeter. Re-solder any joints that appear like those shown in slides 28 to 31.

  38. Student PIC Project Board Inputs & Outputs

  39. For further information on any of these topics please refer to: www.t4.ie

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