diff --git a/tools/kicad/kicad_functions/Cargo.toml b/tools/kicad/kicad_functions/Cargo.toml
index 3873845..a1e71ba 100644
--- a/tools/kicad/kicad_functions/Cargo.toml
+++ b/tools/kicad/kicad_functions/Cargo.toml
@@ -8,4 +8,5 @@ edition = "2018"
 
 [dependencies]
 evalexpr = "6.1"
+regex = "1.5"
 resistor-calc = { git = "https://github.com/racklet/resistor-calc.git", branch = "fix-no-expr_builder-compile", default-features = false }
diff --git a/tools/kicad/kicad_functions/src/lib.rs b/tools/kicad/kicad_functions/src/lib.rs
index 1f9e37f..136bbb6 100644
--- a/tools/kicad/kicad_functions/src/lib.rs
+++ b/tools/kicad/kicad_functions/src/lib.rs
@@ -4,7 +4,7 @@ mod vdiv;
 
 use evalexpr::{EvalexprError, EvalexprResult, Value};
 
-// Match function for all custom functions available in the kicad_rs evaluator
+/// Matching function for all custom functions provided by the kicad_rs evaluator
 pub fn call_function(identifier: &str, argument: &Value) -> EvalexprResult<Value> {
     match identifier {
         "idx" => idx::index(argument),
diff --git a/tools/kicad/kicad_functions/src/vdiv.rs b/tools/kicad/kicad_functions/src/vdiv.rs
index 8c59931..3feb7f8 100644
--- a/tools/kicad/kicad_functions/src/vdiv.rs
+++ b/tools/kicad/kicad_functions/src/vdiv.rs
@@ -2,8 +2,11 @@ use crate::util::err;
 use evalexpr::{
     ContextWithMutableVariables, EvalexprError, EvalexprResult, HashMapContext, Node, Value,
 };
+use regex::Regex;
 use resistor_calc::{RCalc, RRes, RSeries};
+use std::cell::RefCell;
 use std::collections::HashSet;
+use std::ops::Deref;
 use std::panic::panic_any;
 
 fn parse_series(str: &str) -> EvalexprResult<&'static RSeries> {
@@ -18,15 +21,26 @@ fn parse_series(str: &str) -> EvalexprResult<&'static RSeries> {
     }
 }
 
-// evalexpr is not smart enough to distinguish identifiers on its own
-fn unique_identifiers(e: &Node) -> usize {
+fn resistor_identifiers(e: &Node) -> usize {
+    let re = Regex::new(r"^R[1-9][0-9]*$").unwrap();
     let mut set = HashSet::new();
-    e.iter_variable_identifiers().for_each(|i| {
-        set.insert(i);
-    });
+    e.iter_variable_identifiers()
+        .filter(|i| re.is_match(i)) // Match only R? identifiers
+        .for_each(|i| {
+            set.insert(i);
+        });
     set.len()
 }
 
+// Helper for parsing of potentially single-element tuples
+fn parse_tuple(v: &Value) -> Vec<Value> {
+    if let Ok(t) = v.as_tuple() {
+        return t;
+    }
+
+    vec![v.clone()]
+}
+
 struct VoltageDividerConfig {
     target: f64,
     expression: Node,
@@ -34,19 +48,30 @@ struct VoltageDividerConfig {
     series: &'static RSeries,
     resistance_min: Option<f64>,
     resistance_max: Option<f64>,
+    extra_parameters: Option<Vec<Value>>,
 }
 
 impl VoltageDividerConfig {
     fn parse(v: &Value) -> EvalexprResult<Self> {
         let tuple = v.as_tuple()?;
 
-        let resistance_min = tuple.get(3).map(|v| v.as_number()).transpose()?;
-        let resistance_max = tuple.get(4).map(|v| v.as_number()).transpose()?;
+        let resistance = tuple.get(3).map(|v| v.as_tuple()).transpose()?;
+        let resistance_min = resistance
+            .as_ref()
+            .map(|r| r.get(0).map(|v| v.as_number()))
+            .flatten()
+            .transpose()?;
+        let resistance_max = resistance
+            .as_ref()
+            .map(|r| r.get(1).map(|v| v.as_number()))
+            .flatten()
+            .transpose()?;
+
+        let extra_parameters = tuple.get(4).map(|v| parse_tuple(v));
 
-        // TODO: Support external constants
         if let [target, expression, series] = &tuple[..3] {
             let expression = evalexpr::build_operator_tree(&expression.as_string()?)?;
-            let count = unique_identifiers(&expression);
+            let count = resistor_identifiers(&expression);
 
             Ok(Self {
                 target: target.as_number()?,
@@ -55,6 +80,7 @@ impl VoltageDividerConfig {
                 series: parse_series(&series.as_string()?)?,
                 resistance_min,
                 resistance_max,
+                extra_parameters,
             })
         } else {
             err(&format!("unsupported argument count: {}", tuple.len()))
@@ -65,6 +91,16 @@ impl VoltageDividerConfig {
 fn calculate(config: &VoltageDividerConfig) -> Option<RRes> {
     let calc = RCalc::new(vec![config.series; config.count]);
 
+    let mut context = HashMapContext::new();
+    if let Some(v) = &config.extra_parameters {
+        for (i, p) in v.iter().enumerate() {
+            context
+                .set_value(format!("E{}", i + 1).into(), p.clone())
+                .unwrap();
+        }
+    }
+
+    let context_rc = RefCell::new(context);
     calc.calc(|set| {
         if let Some(true) = config.resistance_min.map(|r| set.sum() < r) {
             return None; // Sum of resistance less than minimum
@@ -74,16 +110,17 @@ fn calculate(config: &VoltageDividerConfig) -> Option<RRes> {
             return None; // Sum of resistance larger than maximum
         }
 
-        // TODO: Storing this externally and using interior mutability
-        //  could be helpful to avoid reallocating on every invocation.
-        let mut context = HashMapContext::new();
         for i in 1..=config.count {
-            context
+            context_rc
+                .borrow_mut()
                 .set_value(format!("R{}", i).into(), Value::Float(set.r(i)))
                 .unwrap();
         }
 
-        match config.expression.eval_with_context(&context) {
+        match config
+            .expression
+            .eval_with_context(context_rc.borrow().deref())
+        {
             Ok(v) => Some((config.target - v.as_number().unwrap()).abs()),
             Err(e) => match &e {
                 EvalexprError::DivisionError { divisor: d, .. } => {
@@ -96,22 +133,24 @@ fn calculate(config: &VoltageDividerConfig) -> Option<RRes> {
                             return None;
                         }
                     }
-                    panic_any(e) // No graceful way to handle this from the closure
+                    panic_any(e.to_string()) // No graceful way to handle this from the closure
                 }
-                _ => panic_any(e),
+                _ => panic_any(e.to_string()),
             },
         }
     })
 }
 
 /// `voltage_divider` computes values for resistor-based voltage dividers.
-/// - Usage: vdiv(<target voltage>, <divider expression>, <resistor series>, (min resistance), (max resistance))
-/// - Example: vdiv(5.1, "(R1+R2)/R2*0.8", "E96", 500e3, 700e3)
-/// - Output: (<closest voltage>, <R1 value>, <R2 value>, ...)
+/// - Usage: vdiv(\<target voltage\>, \<divider expression\>, \<resistor series\>,
+///               {(\<min resistance\>, \<max resistance\>)}, ({extra 1}, {extra 2}, ...))
+/// - Example: vdiv(5.1, "(R1+R2)/R2*E1", "E96", (500e3, 700e3), (0.8))
+/// - Output: (\<closest voltage\>, \<R1 value\>, \<R2 value\>, ...)
 /// There can be arbitrary many resistors in the divider, but they must be named "R1", "R2", etc.
 /// The computed optimal resistance values are also presented in this order. The minimal and maximal
-/// resistance limits are optional parameters, and only consider the sum of the resistances of all
-/// resistors defined in the expression.
+/// resistance pair is an optional parameter, and the limits only consider the sum of resistance of
+/// all resistors defined in the expression. The "extra" parameters are optional external inputs for
+/// the divider expression, and will be made available as "E1", "E2", etc. in order.
 pub(crate) fn voltage_divider(argument: &Value) -> EvalexprResult<Value> {
     let config = VoltageDividerConfig::parse(argument)?;
     if let Some(res) = calculate(&config) {