Add operator to convert raw adc units to volt

Interface/Harp.Behavior/AdcToVolt.cs

@@ -0,0 +1,101 @@
+using System;
+using System.ComponentModel;
+using System.Linq;
+using System.Reactive.Linq;
+using Bonsai.Harp;
+using Bonsai;
+
+namespace Harp.Behavior
+{
+    /// <summary>
+    /// Represents an operator that convertes raw ADC values to Volts.
+    /// </summary>
+    [Description("Converts a sequence of raw ADC reads to Volt.")]
+    public class AdcToVolt : Transform<AnalogDataPayload, AnalogVoltData>
+    {
+        /// <summary>
+        /// Converts a <see cref="AnalogDataPayload"/> with raw voltage readings to volts.
+        /// </summary>
+        /// <returns>
+        /// A sequence of <see cref="AnalogVoltData"/> objects representing the converted values.
+        /// </returns>
+        public override IObservable<AnalogVoltData> Process(IObservable<AnalogDataPayload> source)
+        {
+            return source.Select(
+                value => new AnalogVoltData()
+                {
+                    AnalogInput0 = AdcToVoltConverter(value.AnalogInput0),
+                    AnalogInput1 = AdcToVoltConverter(value.AnalogInput1)
+                });
+        }
+
+        /// <summary>
+        /// Converts a sequence of <see cref="Timestamped"/> <see cref="AnalogDataPayload"/> values
+        /// with raw voltage readings to volts.
+        /// </summary>
+        /// <returns>
+        /// A sequence of <see cref="Timestamped"/> <see cref="AnalogVoltData"/> objects representing the converted values.
+        /// </returns>
+        public IObservable<Timestamped<AnalogVoltData>> Process(IObservable<Timestamped<AnalogDataPayload>> source)
+        {
+            return source.Select(
+                value =>
+                {
+                    var payload = new AnalogVoltData()
+                    {
+                        AnalogInput0 = AdcToVoltConverter(value.Value.AnalogInput0),
+                        AnalogInput1 = AdcToVoltConverter(value.Value.AnalogInput1)
+                    };
+                    return Timestamped.Create(payload, value.Seconds);
+                });
+        }
+
+        /// <summary>
+        /// Converts a raw ADC value to volts.
+        /// </summary>
+        /// <param name="adcValue">The raw ADC value to be converted.</param>
+        /// <returns>The converted voltage value.</returns>
+        private static float AdcToVoltConverter(short adcValue)
+        {
+            // Full adc scale 4096 -> 3.3/1.6 = 2.0625V
+            // In practice, HW supports max 5V which translates
+            // to = 15/39 (given by resistor) * 5V = 1.9231 VMax
+            // input to the ADC.
+            // 1.9231V/2.0625V * 4095 = 3818 @ 5V analog input
+            return (float)(5.0 / 3818) * adcValue;
+        }
+    }
+
+    /// <summary>
+    /// Represents the converted values from raw adc units to volts from
+    /// a payload of the AnalogData register.
+    /// </summary>
+    public struct AnalogVoltData
+    {
+        /// <summary>
+        /// The voltage at the output of the ADC channel 0.
+        /// </summary>
+        public float AnalogInput0;
+
+        /// <summary>
+        /// The voltage at the output of the ADC channel 1.
+        /// </summary>
+        public float AnalogInput1;
+
+        /// <summary>
+        /// Returns a <see cref="string"/> that represents the 
+        /// converted AnalogData payload.
+        /// </summary>
+        /// <returns>
+        /// A <see cref="string"/> that represents the 
+        /// converted AnalogData payload.
+        /// </returns>
+        public override string ToString()
+        {
+            return "AnalogVoltData { " +
+                "AnalogInput0 = " + AnalogInput0 + ", " +
+                "AnalogInput1 = " + AnalogInput1 + " " +
+            "}";
+        }
+    }
+}