# Circuit Idea/"Live" Analogies

## "Live" analogies

To show the connection between an analogy and its corresponding circuit diagram, we can "live" the analogy on the monitor screenwith the help of a computer. For this purpose, we can connect the circuit under test by means of an analog-to-digital periphery to a personal computer operating under the control of an appropriate software. An analogy of the studied circuit will be displayed on the screen, which responds adequately to changes in the circuit and thus strengthens associations with it.

### "Live" voltage diagram

Such an arrangement is used in another Wikibooks story to illustrate a more sophisticated version of the Ohm's experiment by a kind of a "geometric analogy". There it is stylized but it can be also thought as a kind of mechanical analogy that can be named "Archimedes double lever" (a lever operated from both its ends).

### "Live" analog scale

For example, in this way we can represent the operation of an op-amp circuit with negative feedback by displaying a "live" analog scale on the screen. Input and output voltages are represented by weights of proportional size on both sides of the scale.

### "Live" discrete scale

Similarly, we can illustrate the operation of an analog-to-digital converter with a discrete weight, where the output value – a digital code – is presented as a sum of reference weights. The picture below shows such a demonstration in the laboratory performed using a MICROLAB system connected to an 8-bit DAC. The PC video output is connected to a multimedia projector.

A stylized image of a mechanical scale is visible on the screen. The left pan houses the analog input weight, and the right pan houses some of the 8 binary standards with weights from 1 to 128. Shown below are the reference voltage (10 V) of the on-board DAC, the input voltage (1.928 V) , the current code (49) and the DAC output voltage (1.914 V).