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-# soundthermo-cpp
+# SoundThermo
 
-Thermometer via sound card. C++ version (Qt)
\ No newline at end of file
+Simple thermometer using sound card input and output, a thermistor and couple of resistors.
+This version uses Qt framework, so it can be built for different OSes.
+
+# 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. This can be done via Qt Creator or simply from command line.
+For building you will need Qt Core and Qt Multimedia.
+
+Firstly it's useful to run `./soundthermo-cpp list`. This will output all detected sound devices in 
+your system, input and output. Note names of desired input and output device.
+
+After that one should run `./soundthermo-cpp measure --input=<INPUT_NAME> --output=<OUTPUT_NAME> --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.
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