EDPS Technical drawing assignment: Student notes

Objective: You are asked to provide the necessary documentation for the design and implementation of a band-pass filter suitable for telephony applications (i.e. an approximate passband between 200 Hz and 4.8 kHz).

Circuit: The first step is to design a suitable circuit for the above task. It is proposed that you use a cascade of a low-pass filter and a high-pass filter with appropriately tuned cut-off frequency points so that the target band-pass specification is achieved i.e. the low-pass cut-off should be lower than the high-pass cut-off to ensure an overlap. Moreover each of the above low- and high-pass filters should be simple passive RC (resistor-capacitor) combinations. The basic theory allowing you to select suitable component values will be reviewed in the lecture.

PCB layout design: Having determinedthe circuit as above, you will need to obtain a PCB layout for this circuit using a computer-aided design package called EasyPC. You are not required to physically construct a PCB board.

The design procedure using EasyPC typically should involve the following:

  • Before running EasyPC, get hold of the actual components you will be using (in our case resistors and capacitors) and make a note of their actual dimensions. Please note that actual component values will, in general, be different from the theoretically derived values in your preparation (below).
  • Start using EasyPC by adding those components to the component library (they are there already, but it helps to know how in case you need to add more complex components in the future).
  • Select the required components from the EasyPC library, position them on the board and label them.
  • Interconnect the above components using appropriate tracks – you need to try one copy with hand-routed tracks and one with autorouted tracks to see how they compare.
  • Add input and output terminals (or “pads” in EasyPC speak).
  • Edit and add any labels as necessary using the appropriate labelling tool including a label for the design as well as another indicating your name(s).
  • Try changing the “pad” and track characteristics (or “styles” in EasyPC speak) i.e. their width and comment on potential advantages/disadvantages
  • Try using more sizeable component-connecting elements (or “shapes” in EasyPC speak) - instead of thin tracks - to produce an alternative layout and comment on potential advantages/disadvantages.
  • Try making the “shapes” connecting directly to the earth more sizeable than all others (and speculate why this could have a practical benefit).
  • Try to modify the “shapes” so that they have rounded corners (and speculate why this could have a practical benefit)

Preparation: Before coming to the lab sessions you should have:

  • analysed the circuit you will be using and developed the equations that determine its response
  • demonstrated that it is suitable for the task in hand by plotting its frequency response (amplitude and phase)
  • determined the component values you will be using

The main element of your report is the documentation. This should include the following elements:

  • A detailed description of the task
  • A higher-level block diagram of the system and a summary of its operation and specifications
  • Lower-level circuit diagrams for each of the low-pass and high-pass filters above
  • A description of the operation of each of the above filters using standard formulas from circuit analysis, an interpretation of these formulas, the determination of the filter cut-off points and plots of amplitude and phase responses.
  • A PCB layout of the overall design as detailed above. Only the final design should be included in the documentation. This should be obtained by removing the so-called “Top-Silk” layer so that component outlining and labels are not included. Intermediate designs can be shown in an Appendix to illustrate the evolution towards the final design or discuss the various options you were asked to try out.
  • Drawings of a box with co-axial input and output sockets for the PCB board to be contained in. Again no physical construction is required just one or more 3D sketches (possibly from more than one views) comprising a box, the board, the sockets and any other auxiliary elements i.e. wiring between the PCB terminals and the sockets, elements allowing the mounting of the PCB to the box etc.
  • A parts / components list.

Word Processing: The workstations running EasyPC are also equipped with MS Word which you may consider using for preparing the documentation.

Assessment: The emphasis is on presentation quality and the expectation is to produce a documentation which looks as professional as possible i.e. tidy, well laid out, easy to follow, clear, illustrative and containing all the required elements.

T. Vlachos, 10/07