Update README.md

README.md

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-# soundthermo
+# SoundThermo
 
-Simple thermometer using sound card input and output, a thermistor and couple of resistors
+Simple thermometer using sound card input and output, a thermistor and couple of resistors.
+
+# Hardware
+
+One should assemble components as shown on scheme below:
+
+![Thermometer scheme](scheme.png)
+
+* Lout should be connected to left channel of sound card output
+* Rout should be connected to right channel
+* Mic In is for microphone input
+* GND should be connected to ground (both on input and output)
+
+# Using the software
+
+First, one should compile the project (target is .NET Core 3.1). After that (assuming your executable 
+is named `SoundThermo.exe` one should enumerate all sound devices in the system with:
+`SoundThermo.exe list`
+
+You will get list of all sound devices with their GUIDs. Identify your device and note its GUID.
+
+After that one should run `SoundThermo.exe measure --input <INPUT_GUID> --output <OUTPUT_GUID> --duration <DURATION>`.
+Duration means amount of time spent for measuring (longer the measurement, more precise results). As for me, one second
+is enough.
+
+# How it works
+
+The idea is to generate harmonic signal with some amplitude `Vin` on sound output and then measure
+`Vout` - amplitude of same signal on microphone input. 
+
+If we consider just left or just right channel, we could not that `Vout = R2 * Vin / (R1 + R2)`,
+where `R1` and `R2` are resistor values. Unfortunately, due to different volumes in input and output,
+really equation is like `Vout = R2 * Vin * k / (R1 + R2)`. So firstly we do measurement via right 
+channel (where we know both `R1` and `R2`), to determine `k`. After that we repeat same measurement
+using left channel. Knowing `Vin`, `Vout`, `R2`, and `k` we can determine value of thermistor. 
+After that we compute real temperature via approximation formula.