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PmodMIC Reference Manual

Note: The Pmod MIC has been replaced by the Pmod MIC3.


The Digilent PmodMIC (Revision B) is a small microphone module with a digital interface. With On Semiconductor's SA575 Low Voltage Compandor and Texas Instrument's ADCS7476 12-bit Analog-to-Digital Converter, you can capture your audio inputs with ease.

Digilent's PmodMIC (click to enlarge)

Features Include:

  • Dynamic Range compressor
  • 12-bit ADC
  • Condenser Microphone

Functional Description

The PmodMIC is designed to digitally report to the host board whenever it detects any external noise. By sending a 12-bit digital value representative of frequency and volume of the noise, this number can be processed by the system board and have the received sound accurately reproduced through a speaker.

The dynamic range compressor on the microphone module helps restrict incoming audio decibels by making the softer sounds louder and the louder sounds softer. The SA575 has its compressor rated for a unity gain level of 0.5 decibels meaning that incoming audio signals will have their decibel level decreased by half, bringing a -40dB signal to -20dB.

Interfacing with the Pmod

The PmodMIC communicates with the host board via the SPI protocol. The 12 bits of digital data are sent to the system board in 16 clock cycles with the most significant bit first. For the ADC7476, each bit is shifted out on each falling edge of the serial clock line after the chip select line is brought low with the first four bits as leading zeroes and the remaining 12 bits representing the 12 bits of data. The datasheet for the ADC7476 recommends that for faster microcontrollers or DSPs that the serial clock line is first brought to a high state before being brought low after the fall of the chip select line to ensure that the first bit is valid. More information about this can be found in our user guide.

Pinout Table Diagram

Pin Signal Description
1 SS Chip Select
2 NC Not Connected
3 MISO Master-In-Slave-Out
4 SCK Serial Clock
5 GND Power Supply Ground
6 VCC Power Supply (3.3V/5V)

The PmodMIC is capable of converting up to 1 MSa per second of 12-bit data, making it an ideal Pmod to use in conjunction with the PmodI2S for an audio development application.

Any external power applied to the PmodMIC must be within 3V and 5.5V to ensure that the on-board chips operate correctly; however, it is recommended that Pmod is operated at 3.3V.

Physical Dimensions

The pins on the pin header are spaced 100 mil apart. The PCB is 1.1 inches long on the sides parallel to the pins on the pin header and 0.8 inches long on the sides perpendicular to the pin header.

Additional Information

The schematics of the PmodMIC are available here. Additional information about the ADC including communication modes and specific timings of the chip can be found by checking out its datasheet here. Similarly, the datasheet for the compandor can be found here

More specific information about how to use the PmodMIC can be found by checking out our user guide. Example code demonstrating how to get information from the PmodMIC can be found here.

If you have any questions or comments about the PmodMIC, feel free to post them under the appropriate section (“Add-on Boards”) of the Digilent Forum.