Building microphone preamp for microcontroller analog input

Microphone is another analog signal sensor which converts sound wave energy into electrical signal. Some microphones does this directly (dynamic microphones), some need additional electrical source like electret. Electret microphone is simply a capacitor which one moving diaphragm which by moving changes capacitance. It can be captured with simple RC circuit. But the signal is very low and barely detectable with microcontroller ADC. This is why normally there are microphone preamp used that gains microphone signal, filters it and gives a DC offset so it would fir perfectly to full rail of ADC input. David actually have made two iterations of microphone preamp circuits. Previous was NPN transistor based which performed pretty good, but this time he wanted to bet even better signal and so he used operational amplifier. He selected TLC272 opamp which can work from single rail and down to 3V which makes it ideal choice for 5V and 3.3V microcontroller circuits. He found that this circuit performs pretty good even on low sound and produces lower noise than NPN version. Bellow you can see how he tested… Continue reading

Speech recognition by bare Arduino

You probably think that speech recognitions is very intense task for processors. In fact it is so if you expect great accuracy and flexibility. But in some cases you simply need electronics to understand few voice commands and perform them with decent accuracy. This is where a μSpeech Arduino library may help. The library is pretty simple and effective. It avoids using FFT but uses voice fricatives to differentiate words. By using simple math to determine words or letters it is able to recognize preselected phrases with up to 80% accuracy. Well you cannot expect much more with Arduino which is very limited in processing power and especially in RAM. Speaking of efficiency – it uses about 160 bytes of RAM to process and takes around 3.2 milliseconds to recognize. So plenty space and power to do other desired tasks controlled by voice. The library is constantly improved that may give even better results. SO this is a great choice for simple voice enabled controls with Arduino. By the way hardware is very simple – single transistor amplified electret microphone… Continue reading

Display a waveforms on VGA monitor

Actually this is great project to show how simple circuit and program can be in order to draw signals on VGA screen. For this only few components are needed like Attiny84 microcontroller running at 20MHz, few caps and resistors. This small circuit is capable to update 800×600 VGA screen at 60Hz refresh rate. It takes Audio signals via ADC channel and displays on screen as a vertical waveform. There is also specially designed preamp that allows to connect an electret microphone to ADC channel so you could see your voice in screen. Continue reading