# Record audio with the MSP430 microcontroller

Posted on Feb 5, 2014

This project uses a small, common electret microphone to convert audio to an electrical signal. These are the cheap microphones found in most PC headsets. The microphone output must be amplified and zeroed before it can be recorded with the MSP430. This is done with an operational amplifier, or op-amp. The op-amp amplifies the tiny, oddly centere

d audio signal into a full range signal based on 0 volts. The diagram shows the original signal (blue) and the amplified, full range signal outputted by the op-amp (red). I`m not much of an analog designer, so may I refer you to any of these tutorials on op-amps if you need more info: wikipedia, a flash tutorial, opamp basics. The op-amp design I used came directly from TI`s digital audio recorder application note slaa123 [pdf!] (page 3). TI`s design uses a TI TLV2252 dual op-amp. We only need one, so I substituted a single channel TI TLV2221 op-amp. I used the circuit and values from the TI app note, but substituted the 2K/. 01uf low-pass audio filter I chose in part II. The TLV2221 is only available in a surface mount package. If you want to do an all through-hole version of this project, consider a TLV2252 based design. We`ll use the MSP430`s on-chip analog-to-digital converter (ADC) to measure the audio signal. The ADC is a pin that measures analog voltages. Measurements taken by the ADC are recorded as a fraction of a voltage reference (Vref). In the prototype, the voltage reference will equal that of the circuit - 3. 3 volts. The smallest voltage change that can be measured by the ADC is denoted in bits. An 8 bit ADC measures voltage on a scale of 0 to 255. A reading of 127 (127/255=50%) from the ADC represents ~1. 65 volts (0. 50 * 3. 3 volt reference). The diagram shows the relationship between bits, voltage...

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