diff --git a/midi2cv/drivers/ad57x4.cc b/midi2cv/drivers/ad57x4.cc
index 42868e0..0295250 100644
--- a/midi2cv/drivers/ad57x4.cc
+++ b/midi2cv/drivers/ad57x4.cc
@@ -1,8 +1,8 @@
 #include "ad57x4.h"
 #include "peripherals.h"
 #include "spi_mode.h"
-#include "stm32f3xx_hal_gpio.h"
 #include <stm32f3xx_hal.h>
+#include <math.h>
 
 static const uint32_t kPinEnable = GPIO_PIN_5;
 
@@ -18,6 +18,29 @@ void AD57X4::Init()
   HAL_GPIO_WritePin(GPIOB, kPinEnable, GPIO_PIN_SET);
 }
 
+void AD57X4::WriteVoltage(uint8_t dac, float voltage) {
+  VoltageRange range = VOLTAGE_RANGE_FIVE_VOLTS;
+  if(fabs(voltage) > 5) range = VOLTAGE_RANGE_TEN_VOLTS;
+  if(fabs(voltage) > 10) range = VOLTAGE_RANGE_TEN_EIGHT_VOLTS;
+
+  float multiplier = 2.0f;
+  if(range == VOLTAGE_RANGE_TEN_VOLTS) multiplier = 4.0f;
+  if(range == VOLTAGE_RANGE_TEN_EIGHT_VOLTS) multiplier = 4.32f;
+  float refin = 2.5f;
+
+  if(voltage < 0) {
+    // convert to signed value
+    int16_t value = (voltage / (multiplier * refin)) * (65535.0f);
+
+    this->WriteDacBipolar(dac, range, value);
+  } else {
+    // convert to unsigned value
+    uint16_t value = (voltage / (multiplier * refin)) * (65535.0f);
+
+    this->WriteDacUnipolar(dac, range, value);
+  }
+}
+
 void AD57X4::EnableAndSetRange(uint8_t dac, VoltageRange range, bool bipolar)
 {
   if (!(this->dacPower & (1 << dac))) {
diff --git a/midi2cv/drivers/ad57x4.h b/midi2cv/drivers/ad57x4.h
index 121b065..1f2f32b 100644
--- a/midi2cv/drivers/ad57x4.h
+++ b/midi2cv/drivers/ad57x4.h
@@ -3,6 +3,7 @@
 #include "stmlib/stmlib.h"
 
 enum VoltageRange {
+  VOLTAGE_RANGE_NONE = 4,
   VOLTAGE_RANGE_FIVE_VOLTS = 0,
   VOLTAGE_RANGE_TEN_VOLTS = 1,
   VOLTAGE_RANGE_TEN_EIGHT_VOLTS = 2
@@ -17,10 +18,16 @@ enum Register {
 
 class AD57X4 {
   public:
-  AD57X4() {};
+  AD57X4()
+  {
+    for (size_t i = 0; i < 4; i++)
+      dacRange[i] = VOLTAGE_RANGE_NONE;
+  };
 
   void Init();
 
+  void WriteVoltage(uint8_t dac, float voltage); // smart range choosing!
+
   void WriteDacBipolar(uint8_t dac, VoltageRange range, int16_t value);
   void WriteDacUnipolar(uint8_t dac, VoltageRange range, uint16_t value);