# New: Add equations to DoCircuits!

Greetings from DoCircuits! Let’s start this blog with a simple experiment. Let’s say you’re asked to perform an experiment to find the power dissipated across a diode. Yes, you would connect a voltmeter and ammeter across a forward-biased diode, run the simulation, and take down the voltage and current across the diode. And finally you have to multiply the V and I values to obtain the power. Tedious isn’t it? How about if you were asked to the power dissipation across the diode with respect to the applied voltage? It’s not impossible. Well let’s see how we can do that too.

Let’s see the circuit that we have to rig up. The resistor is 1 kΩ.

After creating the circuit, click on the “Equations” tab to open the following window:

In the bottom of the equation panel you would find the measuring devices that are connected in the circuit, in this case the voltmeter and the ammeter. Above that you have all the mathematical functions and operators that can be used for your equation. The power equation is V * I. This equation can be added to the experiment as shown below:

Then click on “Add” to save the equation.

Clicking on the equation on the right hand column you can either edit the equation or delete it. In addition to that if you want the equation displayed on the grid along with the circuit for easy working, you can click on “Pin to Grid”.

Now vary the input voltage from 0 to 2 V and run the simulation. Plot the variables in the output plot with respect to the voltmeter value:

The plot shows the IV characteristics of the diode as well the power variation as calculated by the equation.

Thus using the mathematical functions available in the equations panel you can plot calculated variables.

# Transistor biasing in amplifiers and Opamp Voltages

This applies to the problem of proper biasing in transistor amplifiers. Take a look at the diagram shown below:

The biasing on the left is the correct biasing while the one on the left is the incorrect one. The wire from Ci should be should be shorted with the resistor network as shown in the circuit and should not overlap it like the second example. In the case of the wrong biasing, since the base-emitter junction had got no biasing at all, the BJT never gets on and you will not get any output at all from the amplifier. Many people tend to make this mistake and thus the biasing of the BJT is not proper.

Opamp input voltages

When connecting a circuit with an opamp remember that the input voltages given to the opamp should not exceed the Vmax and Vmin values set in the opamp properties. Alternatively while using a five-pin opamp, the input voltages should not exceed the voltages set for the supply voltages for the opamps. If the opamp uses a supply of +15 to -15 V then the input should not cross this threshold. If it does happen  to then the circuit simulation may happen to fail. While designing the circuit, ensure that you give input voltages that do not exceed the voltage limit set by the opamp.

# Don’t forget the ground on both sides of a transformer circuit!

Hi folks, greetings from DoCircuits! It’s great to see everyone having fun learning with DoCircuits. As promised we have been introducing new features and components to enrich your learning experience on a regular basis. We hope you have found them useful and user-friendly. That on one side, we have found some recurring issues related to some type of circuits from the simulations you have run. Let’s try to get those issues addressed in this blog and the ones that follow.

Consider a basic full wave rectifier as shown below:

Note the ground that is connected at the transformer primary to the negative terminal of the input supply. Most circuits that you find online or in text books don’t show this ground and so you may not use it while connecting the circuit. But for our simulator to understand the negative terminal as a reference point a ground has to be connected. If that ground is missed the output will be zero when measured at the input. Similarly if ground is not connected at the secondary you will get an erroneous output.

# A new DoCircuits offline

Hi folks! How is your lab experience going on with DoCircuits? You may have downloaded and used our offline version and you would have noticed that it looks and feels different from the online version and lacks chutzpah  So recently we launched a new, improved and cooler offline DoCircuits for you to work with. You can download it from the following URL: http://www.docircuits.com/download

So how different is it from your online virtual lab? Well apart from the fact that it’s offline, it’s actually a clone of the online version which keeps all your favorite features intact and much more. As you know the free version in DoCircuits.com has limitations but DoCircuits offline, once you get access to it, will be totally unlimited with respect to features.

Welcome screen

The offline version has many advantages compared to the online version:

• Faster simulations. As the simulation need not connect with our servers to obtain the result, simulations take place considerably faster. No more worrying about slow internet connections.
• Save/Load compatibility. Let’s say you are working on the online version and are interrupted while doing an experiment. Save the experiment locally on your disk and that file could be loaded from the offline version and edited.
• Full Version. In addition to the offline tool access the license key that you purchase will allow you full access to all features in the online version and also unlimited simulations and saved circuits.
• Supports Windows for now. But DoCircuits will soon support Linux and Mac.

# Now share your circuit results along with the circuit.

Hey everybody! Hope that you loved the new digital feature that we spoke of in the last post and that you are having fun Doing digital Circuits. So as promised we are adding more features and this new post is about another new feature we’ve introduced in DoCircuits.
Earlier if you were to share a circuit, you would get a link which contained the title of the circuit, its image and its description. But that is just half the job done. What about the result of that particular circuit? Won’t it be more informative if you could share – along with the circuit diagram – its output plot also? Well that’s exactly what you can do now with DoCircuits.
It’s quite easy. After simulating the circuit (if you don’t run the simulation it’s fine as while sharing you will be asked to) click on Share and in the ‘Share’window you will find a button to capture the output screen:

The share window

Click on the Share button. And you will be redirected to the plotter output where after setting which output to plot you can capture the screen image for sharing.