40 lines
1.8 KiB
Markdown
40 lines
1.8 KiB
Markdown
# SoundThermo
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Simple thermometer using sound card input and output, a thermistor and couple of resistors.
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This version uses Qt framework, so it can be built for different OSes.
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# Hardware
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One should assemble components as shown on scheme below:
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* Lout should be connected to left channel of sound card output
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* Rout should be connected to right channel
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* Mic In is for microphone input
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* GND should be connected to ground (both on input and output)
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# Using the software
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First, one should compile the project. This can be done via Qt Creator or simply from command line.
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For building you will need Qt Core and Qt Multimedia.
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Firstly it's useful to run `./soundthermo-cpp list`. This will output all detected sound devices in
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your system, input and output. Note names of desired input and output device.
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After that one should run `./soundthermo-cpp measure --input=<INPUT_NAME> --output=<OUTPUT_NAME> --duration=<DURATION>`.
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Duration means amount of time spent for measuring (longer the measurement, more precise results). As for me, one second
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is enough.
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# How it works
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The idea is to generate harmonic signal with some amplitude `Vin` on sound output and then measure
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`Vout` - amplitude of same signal on microphone input.
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If we consider just left or just right channel, we could not that `Vout = R2 * Vin / (R1 + R2)`,
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where `R1` and `R2` are resistor values. Unfortunately, due to different volumes in input and output,
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really equation is like `Vout = R2 * Vin * k / (R1 + R2)`. So firstly we do measurement via right
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channel (where we know both `R1` and `R2`), to determine `k`. After that we repeat same measurement
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using left channel. Knowing `Vin`, `Vout`, `R2`, and `k` we can determine value of thermistor.
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After that we compute real temperature via approximation formula.
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