HARDWARE DESIGN PROCEDURE
STEP TAKEN WHILE PREPARING CIRCUIT
(A) PCB DESIGNING :-
The main purpose of printed circuit is in the routing of electric currents and signal through a thin copper layer that is bounded firmly to and insulating base material some time called the substrate. This base is manufactured with integral bounded layers of thin copper foil which has to be partly etched of other wise remove to arrive at a pre designed pattern to suite the circuit connections or whatever other application is noted.
The term printed circuit board is derived from the original method where by a printed pattern is used as the mask over wanted areas of copper. The PCB provides an ideal baseboard upon which to assemble and hold firmly most of the small components.
From the constructor’s point of view, the main attraction of using PCB is its role as the mechanical support for small components. There is less need for complicate and time consuming metal work of chassis contraception except perhaps in providing the final enclosure. Most straight forward circuit designs can be easily covered into printed wiring layer, the thought required to carry out the inversion cab footed high light as possible because error that would otherwise be missed in conventional point to point wiring .The finished project is usually neater and truly a work of art.
Actual size PCB layout for the circuit shown is drawn on the copper board. The board is then immersed in FeCl3 solution for 12 hours. In this process only the exposed copper portion that is etched out by the solution.
Now the petrol washes out the paint. Now the copper layout on PCB is rubbed with a smooth sand paper slowly and lightly such that only the oxide layers over the Cu is removed. Now the holes are drilled at the respective places according to component layout.
(B) LAYOUT DESIGN :-
When designing the layout one should observe the minimum size (component body length and weight). Before starting to design the layout we need all the required components in hand so that an accurate assessment of space can be made. Other space consideration might also include from case of mounted components over the printed circuit board or to access path to present components.
It might be necessary to turn some components round to a different angular position so that terminals are closer to the connections of the components. The scale can be checked be positioning the components on the squared paper. If any connection crosses, then one can reroute to avoid such condition.
All common or earth lines should ideally be connected to a common line routed around the perimeter of the layout. This will act as the ground plane. If possible try to route the outer supply line to the ground plane. If possible try to route the other supply lines around the opposite edge of the layout to through the center. The first set is tearing the circuit to eliminate the crossover with out altering the circuit detail in any way.
Plan the layout looking at the topside to this board. First this should be translated inverse later for the etching pattern large areas rate recommended to maintain good copper adhesive it is important to bear in mind always that copper track width must be according to the recommended minimum dimensions and allowance must be made for increased width where termination holes are needed. From this aspect, it can become little tricky to negotiate the route to connect small transistors.
There are basically two ways of copper interconnections pattern in the under side to the board. The first is the removal of only the amount of copper necessary to isolate the junction to the components to each other resulting in the large areas of copper. The second is to make the interconnection pattern looking more like conventional point wiring by routing uniform width of copper from component to component.
(C) ETCHING PROCESS :-
Etching process requires the use of chemicals acid resistant dishes and running water supply. Ferric chloride is mostly used solution but other etching materials such as Ammonium per Sulphate can be used. Nitric acid can be used but in general it is not used due to poisonous fumes.
The pattern prepared is glued to the copper surface of the board using a latex type of adhesive that can be cubed after use. The pattern is laid firmly on the copper using a very sharp knife to cut round the pattern carefully to remove the paper corresponding to the required copper pattern areas. Then apply the resist solution, which can be a kind of ink proportion for the purpose of maintaining smooth clean outlines as far as possible. While the board is drying, test all the components.
Before going to next stage, check the whole pattern and cross check against the circuit diagram. Check for any free metal on the copper. The etching bath should be in a glass or enamel disc. If using crystal of ferric- chloride these should be thoroughly dissolved in water to the proportional suggested. There should be 0.5 lt. of water for 125 gm of crystal.
Waste liquid should be thoroughly deflated and dried in water land. Never pour down the drain. To prevent particles of copper hindering further etching, agitate the solutions carefully by gently twisting or rocking the tray.
The board should not be left in the bath a moment longer than is needed to remove just the right amount of copper. Inspite of there being a resistive coating there is no protection against etching away through exposed copper edges. This leads to over etching. Have running water ready so that etched board can be removed properly and rinsed. This will halt etching immediately.
Drilling is one of those operations that call for great care. For most purposes a 1mm drill is used. Drill all holes with this size first those that need to be larger can be easily drilled again with the appropriate larger size.
(D) COMPONENT ASSEMBLY : –
From the greatest variety of electronic components available, which runs into thousands of different types it, is often a perplexing task to know which is right for a given job.
There could be damage such as hairline crack on PCB. If there are, then they can be repaired by soldering a short link of bare copper wire over the affected part.
The most popular method of holding all the items is to bring the wires far apart after they have been inserted in the appropriate holes. This will hold the component in position ready for soldering. Some components will be considerably larger. So it is best to start mounting the smallest first and progressing through to the largest. Before starting, be certain that no further drilling is likely to be necessary because access may be impossible later.
Next will probably be the resistor, small signal diodes or other similar size components. Some capacitors are also very small but it would be best to fit these after wards. When fitting each group of components mark off each one on the components as it is fitted and if we have to leave the job we know where to recommence.
Although transistors and integrated circuits are small items there are good reasons for leaving the soldering of these until the last step. The main point is that these components are very sensitive to heat and if subjected to prolonged application of the soldering iron, they could be internally damaged.
All the components before mounting are rubbed with sand paper so that oxide layer is removed from the tips. Now they are mounted according to the component layout.
(E) SOLDERING : –
Flux is applied to the tips and then the components are soldered. Now the board is prepared. Antenna and condenser mike are connected at respective place and 9v dc supply is given.
Project has following limitations:
- Infrared waves can not pass through solid objects because of their long wavelength.
- LOS and restricted communication range.
- There is no feedback arrangement, after the data transmission transmitter can not know whether data is received by receiver or not.
The objective of project is to make high speed wireless LAN using sequence detector for secure data transmission. The principle and technique used in project can be used to make wireless Local Area Network (LAN) in an office where several computers are connected to each other besides providing provision for security.
Hence, our project will be very useful for wireless networking for short range secure data communication.
 Computer Networks by Andrew S. Tanenbaum (3rd Edition)
 Microwave and Radar Engineering by M. Kulkarni
- ABHAY BHISIKAR
- AVINASH GAJBHIYE
- KABINDRA YADAV
- NILESH MORE
- VIJENDRA KATARE
- VIKAS SHARMA
- VIKAS WARUDKAR