How to simulate voltage controlled resistors and potentiometers in EasyEDA. 

Resistors in spice cannot be set to zero. They must always have a small minimum value.  
Resistors should also not normally be allowed to go negative. 
So, to prevent them transitioning through zero and also to stop them going negative, the 
resistors in these examples use the LIMIT function to apply upper and lower limits to 
their values. 
 
The resistor, R1, has a value, R1val, that is scaled by the controlling voltage, V(CTRL). 
It has a minimum positive resistance defined by R1min and, to prevent accidentally setting  
a resistance above the generally recommended maximum value of 1G due to a combination of 
R1val and the maximum applied V(CTRL), R1max is set to 1G. 
 
The pot in this example is controlled by a voltage that represents the angular rotation of 
the pot spindle, in degrees. It has an end to end resistance value, Rpotval.
The resistance making up each side of the slider has a minimum positive resistance defined by 
Rpotmin and, to prevent accidentally under or over-rotating the pot via the controlling voltage, 
it has a minimum and maximum resistance limits, Rpotmin and Rpotmax.
 
F8 to run.