Choose the Right Online Engineering Calculators and Design Tools

13 April 2023

From this week, EPDT will feature a four-part series from Mouser discussing some of the challenges design engineers face and how online tools can help.

In the first article in the series, Mouser's Mark Patrick looks at "Tips for Choosing the Right Online Engineering Calculators and Design Tools"

Designers need to perform various calculations when creating a circuit. For everything from simple component selection to designing analog filters and radio frequency (RF) circuits, tools are available to help.

An Overview of the Design Process

Circuit design is a complicated process. The designer needs to understand the mathematical theory underlying the system’s behaviour and the individual components. 

The complexity of calculations depends on the type of design. For example, all designers must know Ohm’s law, which relates voltage, current, and resistance. But specific fields require more complex and involved analysis.

Audio filter designers will need to calculate the frequency response and stability of the circuit using mathematical tools such as Laplace or Z transforms. Designing radio-frequency circuits can involve the application of Maxwell’s equations, which describe the propagation of electromagnetic waves. 

In addition to understanding the components that form their circuit, engineers need to consider “parasitic” components. These are the resistance, inductance, and capacitance inherent in the connections between components. Although these typically have very small values, correctly accounting for them can be critical to the system’s optimum performance.

Using Design Tools
Doing even straightforward calculations repeatedly can be tedious and error prone. For more complicated systems, the calculations can be difficult and time-consuming. Design tools can accelerate the design process and reduce errors.

To support their products, manufacturers provide a range of resources including data sheets, reference designs, and, increasingly, the tools to perform design calculations and simulations. 

Figure 1: Screenshot of TI Calculator (Source: Texas Instruments)
Figure 1: Screenshot of TI Calculator (Source: Texas Instruments)

These can help design engineers understand the device and system-level behaviour and assist with component selection.

Simulation tools allow the designer to provide input signals and check the output to confirm that their circuit works as intended.

Many of these design tools are available online. Some, especially the simpler calculators, run directly in the browser. Others are offered for free from manufacturers or third-party websites.

The Simplest of Calculators
An example of a simple-to-use, readily-available calculation tool is Texas Instruments’ Analog Engineer’s Calculator (Figure 1). 

It runs on a PC, has a graphical interface, and assists with many routine calculations. 

Some of the functions available:
    • Solving simple circuit problems using passive components
    • Calculating the feedback resistors to set the gain of an op-amp
    • Estimating parasitic effects in a PCB
    • Designing with analog-to-digital converters (ADCs) and digital-to-analog converters (DACs)
    • Determining the output values from various types of sensors

Simulators are a valuable tool for checking the correctness of a design before constructing it and can therefore save both time and money. They work at various levels of abstraction. For example, an analog circuit simulator can model the precise response of every component in the system as voltages change over time. Alternatively, a simulator for digital logic will represent the values 0 and 1 at each clock period without worrying about the exact voltage and timing.
The SPICE Analog Circuit Simulator
A widely used analog circuit simulator is SPICE (Simulation Program with Integrated Circuit Emphasis). Created in 1973, it has become an industry-standard tool. Many manufacturers provide models of their components for use with SPICE. 

Figure 2: Screenshot of LTspice (Source Analog Devices)
Figure 2: Screenshot of LTspice (Source Analog Devices)

Some manufacturers also provide their own SPICE-based simulators. For example, Analog Devices offer LTspice (Figure 2) as a free download for Windows or MacOS. This comes with a library of SPICE models from Analog Devices, Linear Technology, Maxim Integrated, and others. 

LTSpice can be used for: 

    • Radio frequency circuits
    • Power electronics
    • Audio system
    • And many other circuits

The designer enters a schematic of an electronic circuit to be simulated and provides the input signals, and LTspice’s waveform viewer shows the results of the simulation. It also includes tools to analyse the system in various ways.

A Circuit Simulator for Mobile Use
EveryCircuit [] is a very different tool. This is an interactive schematic capture and circuit simulator that runs on Android and iOS devices, meaning that a designer can enter and run circuit simulations anywhere, on their phone or tablet. For evaluation, there is a free trial version.

EveryCircuit’s great strength is its simple user interface and interactivity. You can change circuit parameters as a simulation runs and see the results immediately, making it a good tool for learning and experimenting. However, it does not have the same range of support for commercial components as Ltspice and similar tools, but it is community supported, so may improve over time.

Other General-Purpose Calculators 
There are many online calculators for solving circuit specific design problems. These include unit conversion and looking up resistor colour codes. There are also tools for calculating resistor values and the timing behaviour of resistance-capacitance (RC) and inductance-capacitance (LC) circuits.

You can find some examples on the Mouser Conversion Calculators page. 

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