Circuit Analysis using Virtual Instruments in Proteus

This chapter is part of our Proteus Tutorial series. In this chapter we explain circuit analysis using virtual instruments in Proteus.

 Oscilloscope

Proteus provides oscilloscope, which is a very essential instrument for analysis purpose. The Digital Storage Oscilloscope is featured as:

• 4-Channel input
• 2 MHz sampling frequency
• Invert option for each channel
• Relational output between channels
• Input coupling type selection
• Source selection between channels
• Adjustable Volts/Div through Knob or manual entry in textbox
• Auto/One-shot selection for output update
• Cursor placements for detailed and accurate observations
• Finally, analysis printing option, which made it Digital Storage Oscilloscope.

These options will be very handy for the designer to make a real-time analysis of the circuit. The oscilloscope is listed under the Virtual Instruments category.

Step 1: – Select Virtual Instruments mode and choose Oscilloscope by Double-Click.

Step 2: – Place the instrument in the workspace like any other component.

Step 3: – Run simulation by Clicking on the Play button.

5.2 Features explained

The inputs connected to every channel are shown in the scope with reference to GND terminal by default. There are four such channels namely, Channel A, B, C, D.

Signals of a minimum time period from 0.5 µS can be analyzed i.e. signals up to 2 MHz frequency can be analyzed.

For the explanation purpose, a sine wave is selected here. Here the same sine wave signal is connected to both channels A & B.

Inputs connected to each channel can be viewed with invert option. Connect the signal to any channel and choose invert option during simulation.

Addition and Subtraction of inputs can be done using A+B and C+D options for the inputs connected to respective channels.

Subtraction is achieved by inverting the respective channel before adding i.e. if A-B has to be done, then invert the channel B and then use A+B option. DC coupling mode has to be chosen for mathematical operations.

Coupling mode also can be selected for analyzing AC as well as DC signals i.e, for digital signals, DC mode can be selected and for signals coming from Op-Amps, inverters like sine wave generators etc with dual voltage rails, AC mode can be selected. Similarly, a source can be selected for the trigger and edge selection is also available for the trigger.

Volts/Div can be adjusted through knob or value can be directly entered in the text box for each channel individually. The simulation result can be updated continuously by choosing the Auto mode or can be paused at any required instant by selecting One-Shot mode or by Unselection of Auto mode. This feature is useful while recording the circuit behavior at any required instant.

Cursors provided help the designer to note accurate values. Select cursor mode and place the cursor on the grid or signal at a point where the voltage and time parameters are required. Unselect the cursor mode to remove the cursors.

The simulated waveforms can be documented by Print option of the oscilloscope which is useful for presentations, sharing or recording the analysis i.e. for storage purpose thus making the scope as Digital Storage Oscilloscope. Right-Click on the scope during simulation and select Print option.

The graphics like colours of the channels can be changed to bring the desired view by using setup option. This option is in Right-Click tab of the scope

5.3 Voltmeters and Ammeters

Along with the detailed analysis instrument like an Oscilloscope, there are simple instruments like Voltmeter and Ammeter. These are available in both AC and DC modes. The resolution of the meters can also be set to Volts, milli volts and Amps, milli Amps etc.

Volt and Ammeters are listed under the Virtual Instruments category.

Step 1:- Select Virtual Instruments mode and choose required meter by Double-Click.

Step 2:- Place the instrument in the work space like any other component.

Step 3:- Connect the meters in the proper way i.e.., Voltmeter in parallel to the load and Ammeter in series to the load.

Step 4:- Run simulation by Clicking Play button.

Scale/resolution can be changed in the edit properties tab. Stop the simulation and Right-Click on the instrument or Double Click on the instrument for Edit properties tab. Change the Scale to desired units.

5.4 Digital Circuit Analyzers

There are dedicated instruments for analyzing Digital circuits. Logic analyzer, Virtual terminal, I2C Debugger, SPI Debugger are available to analyze microcontroller related communicational interface circuits.

Virtual terminal is used to connect UART modules to the COM ports either RS-232 or USB and exchange data between computer and external modules by using COM Port component in workspace.  Physical PORT being used can be selected and data frame can be set to desired values using Edit properties tab of the Com Port.

Similarly, other instruments can be used in microcontroller circuits and the data can be exchanged between modules and microcontroller either virtually or by connecting external hardware.