Compact Current Meter - Fall 2012

Dynamic DC does a nice job of showing DC currents for most components, but not for macros, subcircuits, and OPAMPs. Since there is no built-in way to measure the currents into or out of these components it would be nice to have a simple way to measure the currents. For example, consider this circuit:. The currents flowing into the + and - OPAMP input pins are not shown. The usual way to measure currents in a circuit where they are not otherwise available is to use 0V batteries like this: This works well enough, but the batteries look a little out of place and to someone who doesn't know, they seem pointless since they are 0V. Now consider this circuit. Here we've placed a simple current meter in the branches where we want to see the current flow. What is the Current Meter? As you can see by looking at its Component Editor entry its definition is Battery and it uses a shape called CurrentMeter, created expressly for the purpose of showing its purpose. Of course, when you place the first one of these in a schematic, it will pop up the Attribute dialog box and ask for the battery's value. Enter 0. It will not normally display this value which is what you want. You may want to disable the Show Check box next to the PART value so that the NAME does not show and get in the way of the current reading. Do you have to do all this every time you add a current meter? You don't if you use CTRL + mouse drag to create the next one. If you've never used CTRL+drag, you're in for a treat. It is the fastest way of creating and placing a component, especially one that is identical to an existing one. To use CTRL + drag simply press and hold the CTRL key. Place the mouse over the part and click the left mouse button. Drag the part to where you want, then release the mouse button. Presto, you have an exact copy of the part. The big advantage here is that you only have to enter the 0 value and disable the PART attribute printing once. Thereafter it's a simple CTRL + drag to place another part. The CTRL + drag procedure is especially useful when duplicating large parts of a circuit, such as the differential pair of an amplifier. If you download the circuit CurrentMeter, it will import the Current Meter component and its shape, CurrentMeter into the Import section of the Component library where it will be available for use in other circuits.