The -VE should better be connected to 0V. In your circuit with В±5V on the sensor, it probably would вЂexplodeвЂ™. One point is that the power supply voltage is 5V. You definitely have to look at the data sheet. The humidity then may be represented by a voltage source. But why not replace them by an electrical node, say a voltage input with 0V for 0% and 100V for 100% humidity? If you want to follow this idea (very common in sensor design), you have to add another pin (e.g. Of course KiCAD and ngspice donвЂ™t have any notion of humidity nodes. A sensor has another connection to the environment, the humidity entrance. You correctly have shown 3 electrical pins in your sensor symbol. The reliable source available is the data sheet from Honeywell. There seems to be no Spice model available from the vendor. More difficult will be handling the sensor. Concerning the power supply, better choose ngspice compatible symbols as you may find in the Simulation_Spice symbol library. This tutorial will give you also some hints on establishing PSPICE compatibility, typically needed for using commercial OpAmp models. Then you have to add this model to your OpAmp symbol. For the OpAmp LM321 you might google for a suitable vendorвЂ™s Spice model. To do a simulation, each symbol will need a Spice model. The simulation up to now has spitted a lot of error messages, most dealing with missing models. In designing the circuit diagram, you have used KiCAD symbols.

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