Circuit design is the elaborate process to make an electronic circuit to satisfy a requirement. It covers simple electronic circuits to elaborate circuits that operate very large electronic systems. Simple circuit design can be done by a person, but complex circuit design requires team work and a systematic approach. The design of circuit depends upon the mind and approach of the designer. Some designers stick on too much theory while most designers are practical since the reader do not want to go deep into the theoretical aspects but wants to know how it is working and what is its purpose.
Theoretical calculations are necessary for selecting the components but some factors are beyond our control. Some designers select the components by calculating the current or voltage flowing through the component, ignoring the tolerance and other physical parameters of the components. If we select 1K resistor by calculating the current requirement using Ohms law, the result will not be as per the formula since 1K resistor will not have 1000 ohms but it may be either 900 ohms or 1100 ohms. Tolerance of components, their make, quality, temperature etc considerably affects the working of the circuit. So a wise designer will select the components by considering the average performance of the component. Some critics comment on the selection of a particular component in a circuit by considering only theory but practically that is not the case. Remember, a functional circuit can be designed in different ways depending up on the approach of the designer. Only after bread board testing, we can assess the working of the circuit.
Design of circuit is also very important. Circuit diagram reflects the mind and approach of the designer. Simple circuits are more attractive than complex circuits. Some designers try to confuse readers by making the circuit more complex and they believe that, adding more components will increase the performance.Some circuit designers explain the working of circuits by giving elaborate description of the working of components. This is really boring and confusing because even an average hobbyist knows how a transistor works or a resistor limits current. Such elaborate description is suitable for Tutorials. The write up should be simple and precise. Then only the reader can concieve the idea easily.A simple oscillator can be designed using 555 IC and a few components. Ignoring this fact, some designers use large number of transistors, capacitors and resistors to make an oscillator. The most important thing is that the constructor requires minimum components and minimum time to make a functional circuit. Most constructors select simple circuits to make the gadget compact.
The following steps are involved in circuit design process.
1. Preparation of Schematics
Circuit schematic is the combination of circuit diagram and schematics. The circuit diagram is the conventional graphical representation to show the working of the circuit while the schematics represent the use of graphic symbols in the diagram. The layout of symbols in the circuit diagram may not resemble the layout of the physical circuit. In the circuit diagram, the symbols are placed in a convenient way for easy identification of its location and working. Simplified standard symbols are used in circuit diagram to represents components. The interconnections in the circuit diagram, does not corresponds to the actual location of the components in the PCB. The circuit diagram explains how the components are connected each other and work together. The main purpose of the circuit diagram is to make PCB and for the trouble shooting or maintenance of the circuit.
After creating the diagram, through hand drawing or using software like CAD programme, it is necessary to select the appropriate components. To select the components, current requirement, voltage requirements, output nature etc are to be considered to meet the specific requirements. A well experienced person can select the components easily and can calculate the voltage and current requirements using Ohms law and other mathematical formula. Errors in the selection of components can be corrected during bread board testing.
If circuit simulation software is available, it is better to simulate the working of the circuit before breadboard checking. Simulation will show the exact working of the circuit.
4. Bread board assembling
Bread board is the kind of prototype board with electrical connections to place components. All the components including ICs can be easily inserted into the sockets of bread board. The advantage of bread board is that, we can easily remove and replace components if the working is not perfect. Electrical connections can be made using hook up wires.
5. Corrections and trouble shooting
In the bread board testing, sometimes the circuit will not work or shows erratic response. These can be corrected by selecting appropriate components and changing the circuit design. If the circuit is perfect in bread board testing, we can directly go to the construction.
6.Construction of circuit
Construction requires a PCB and soldering procedure. PCB can be designed using the PCB design software and can be made in copper clad board using the standard PCB making protocol. Etching, Tinning, Drilling, Masking and Legend making are the different stages involved in PCB making.Click links to see PCB making and Soldering technique.
7. Testing and corrections
Before making many PCBs, it is better to make a Test PCB first to test the working of the circuit. Assemble the PCB as per the circuit diagram and solder them correctly. Power the circuit and test for its performance many times. If the required performance is achieved, you can make multiples of the PCB as per the requirements.
Circuit design for commercial applications
If the circuit is meant for making commercial gadgets, it is necessary to consider all the requirements of the customer and its fail proof operation. Circuit design for commercial applications involves the following stages.
1. Specification of circuit
This is the functionality of the product. It involves, size, shape, weight, current rating etc of the circuit. The specification involves the detailed description of the circuit, electrical description, how the circuit receives input signals and output characteristics, power consumption etc. When the design process progresses, the designer stick on to tighten the specification considering the requirements of the gadget. More tests will be carried out to satisfy the working of the gadget. Only after getting satisfied result, the designers fix the design for the circuit.
2. Black box designing
Diagram showing the functional stages of the circuit is known as Block diagram or sometimes called as Black box design. This system is viewed in terms of the input, output and transfer characteristics of the gadget without knowing the details of the internal circuitry. It is called as Black box since the internal details are opaque (black) in the block diagram. In contrast to the black box diagram, there is White box diagram in which the internal details of the gadget are visible. Block diagram helps the designer to divide the complex circuit in to sections based on the functions so that interpretation of the result becomes easier.
3. Lay outing
This is the preparation of the actual circuit and determination of the position of each component. During layout, the physical position and the electrical connection of each component is determined. This layout finally reflects in the PCB design. The layout stage is difficult and time consuming, since the selection of particular components is important. If a component like IC is decided, sometimes it will not be easily available. So again the lay out changes with another component of similar functions. Careful Catalogue engineering helps to decide the type and features of components before making the final layout.
4. Testing and Prototyping
Once the circuit is designed, it should be properly tested before fixing the final design. Verification of each stage of the circuit is very important to get the final result. This requires mathematical applications and computer simulations since the designer should confirm the working of each part to satisfy the needs of the consumer. At least one prototype should be made using the specified components for physical testing. Prototyping is the method of exploring the working before investing amount to the circuit. Bread board prototypes can be made at any stage during the design process so that corrections can be made in each stage to finalize the sections in the block diagram. Mock packaging of the circuit is also made to see how the gadget is in appearance.
5. Cost analysis and Documentation
During circuit design, it is important to assess the cost of the whole gadget. This cost analysis helps to make low cost and reliable circuits. For example, ICs are the most costly components and careful selection of low cost and reliable ICs will reduce the cost considerably. Power supply section is also costly. If SMPS power supply is used, cost and size of the gadget can be reduced to great extent. Documentation includes the specification of the circuit, its working, testing procedures, wiring diagram, installation methods, warranty features etc. Without a well documentation, the consumer will not satisfy with the gadget, since the consumer wants to know all the details of the gadget.
6. Product release and Marketing
Final stage of the design process is the release of the circuit in physical form. It should be tested OK before releasing into the market. Well tested, warrantied product wilh attractive features will definitely attract the consumers. Consumers want to satisfy their needs at moderate cost and at the same time wants to know its durability and reliability. A well designed circuit will not breakdown.