diff --git a/firmware/lambda_conversion.cpp b/firmware/lambda_conversion.cpp
index 70a5ba5..8a170a7 100644
--- a/firmware/lambda_conversion.cpp
+++ b/firmware/lambda_conversion.cpp
@@ -1,7 +1,8 @@
 #include "lambda_conversion.h"
 #include "sampling.h"
+#include "port.h"
 
-static float GetPhi(float pumpCurrent)
+static float GetPhiLsu49(float pumpCurrent)
 {
     // Maximum lambda ~2
     if (pumpCurrent > 1.11f)
@@ -22,6 +23,46 @@ static float GetPhi(float pumpCurrent)
     return gain * pumpCurrent + 0.99559f;
 }
 
+static float GetPhiLsu42(float pumpCurrent)
+{
+    // Maximum lambda ~2
+    if (pumpCurrent > 1.19f)
+    {
+        return 0.5f;
+    }
+
+    // Minimum lambda ~0.7
+    if (pumpCurrent < -1.85f)
+    {
+        return 1 / 0.7f;
+    }
+
+    // This estimation is accurate within 0.5% from 0.8 to 1.0, and 0.01% from 1 to 1.2 lambda when compared to the lookup table in the Bosch datasheet
+    // This error is less than half of the claimed accuracy of the sensor itself
+    float gain = pumpCurrent < 0 ? -0.23505f : -0.41441f;
+
+    return gain * pumpCurrent + 0.99153f;
+}
+
+static float GetPhiLsuAdv(float /*pumpCurrent*/)
+{
+    // TODO
+    return 1;
+}
+
+static float GetPhi(float pumpCurrent) {
+    switch (GetSensorType()) {
+        case SensorType::LSU49:
+            return GetPhiLsu49(pumpCurrent);
+        case SensorType::LSU42:
+            return GetPhiLsu42(pumpCurrent);
+        case SensorType::LSUADV:
+            return GetPhiLsuAdv(pumpCurrent);
+    }
+
+    return 1;
+}
+
 float GetLambda(int ch)
 {
     float pumpCurrent = GetPumpNominalCurrent(ch);