# How to mathematically represent an electric and electronic circuit diagram.

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#### arunkumar413

##### New Member
Hi Team,

I want to represent a circuit diagram in a mathematical way (Not the electrical behavior of the components). Just the connections between different components. For example below this circuit is a diagrammatic representation of the connections between various components. How do I represent this in a mathematical way.

How to do it.

Thanks,
Arun

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#### JonSea

##### Well-Known Member
A net list shows all the connections between components. this is sort of what you're asking.

#### MikeMl

##### Well-Known Member
A common method is the way Spice does it. Number (or otherwise uniquely name) each electrical node in the circuit topology. Then each component is defined with pins. Some components have two pins (resistors, capacitors, diodes), others have more pins (pot, transistor). On some components, the pin order doesn't matter (resistors), on some it does, (polarized capacitor, diode, battery, transistor).

I let LTSpice do it for me. First, I built the circuit. I didn't have a three terminal pot model for VR1 on this computer, so I improvised using a parameter w for pot wiper position (0.001<=w<=0.999):

In order to simulate the circuit, LTSpice automatically converts the graphics above into a text-based .net file. This describes how the components are hooked up, and what values they have:

Note that I explicitly labeled some nodes (gnd, b, c, cc) and LTSpice made up names for the rest (N001, N002).

To read the netlist, note that the battery is V1, with its positive terminal connected to node cc, its negative terminal connected to node 0 (gnd), and it has a value of 9V. Another example: Q1 has its collector connected to node c, base to node b, emitter to node 0 (gnd), and is a BC547. The LED is connected anode to node N001 and cathode to node c.

Google Spice netlist for a definition of this method of describing circuit topology.

btw- your circuit is a very poor design. Very temperature sensitive, and D1 barely turns on even with the pot all the way at the top...

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