MSGEQ7 8x8matrix

Spectrum analyzer display using MSGEQ7, 8x8 bicolor matrix and Arduino Uno. Input is from a head phone jack or microphone.

Demo

Short but powerful.

Clone

Clone the repository and its submodules to a local directory. The --recursive flag automatically initializes and updates the submodules in the repository.

git clone --recursive https://github.com/cvonk/MSGEQ7_8x8matrix.git

or using ssh

git clone --recursive [email protected]:cvonk/MSGEQ7_8x8matrix.git

Hardware

This project uses input from headphone input or amplified microphone and outputs to a 8x8 bicolor matrix.

Schematic

Power

Logic

A few notes:

• The 200 kΩ resistor is not an E12-series value. You can also make an equivalent value by 220 kΩ and 2.2 MΩ in parallel, or put two 100 kΩ in series.
• If there is noise, try adding a 47 μF across the power rail.
• I put the MSGEQ7 and its glue on a piece of proto board.
  

Bill of materials

Make sure the MSGEQ7 is authentic. It should draw about (0.8,\rm{mA}); pin 6 should have a reference voltage of about (2.5,\rm{V}) and have an indentation near pin 1.

Name	Description	Suggested mfr and part#	Paid
PCB1	Arduino Uno R3 or compatible	Adafruit 2488	$17.50
PCB2	Bicolor LED Square Pixel Matrix w/ I2C breakout	Adafruit 902	$15.95
PCB3	Electret microphone w/ auto gain control	Adafruit 1713	$7.95
U1	Seven Band Graphic Equalizer Display Filter	MSI MSGEQ7	$5.50
J1	Headphone jack stereo connector, 3.5mm, kinked pin	Kycon STX-3120-5B	$0.74
R1, R2	Resistor, 22 kOhm, 1%, 1/8 W, 0805	Yageo RC0805FR-0722KL	$0.10
R3	Resistor, 200 kOhm, 1%, 1/8 W, 0805	Yageo RC0805FR-07200KL	$0.10
C1, C2, C3	Ceramic capacitor, 0.1 µF, 25V, 0805	KEMET C0805C104M3RACTU	$0.10
C4	Ceramic capacitor, 33 pF, 50V, 0805	KEMET C0805C330J5GAC7800	$0.10

Notes

The popular Arduino UNO R3 forms the heart of the system. This board is now getting hard to find, but you can also use the Arduino METRO 328 or any other equivalent boards.

For the microphone, I use the Adafruit microphone breakout, because includes an automatic gain control. Other microphones will work for as long as the output signal is strong enough.

Software

The implementation changes the sound wave to an electrical signal; uses autocorrelation to find frequency played; display frequency as note on screen while sending to a MIDI synthesizer.

Requirements

Component	Version tested
Arduino IDE	1.8.19
Arduino AVR Boards	1.8.5
Adafruit LED Backpack library	1.3.2
Adafruit GFX library	1.11.1

Build

• Install the libraries.
• Using the Arduino IDE or Visual Code
  • Specify the board and COM port.
  • Build and upload the sketch .

Details

The MSI MSGEQ7 measures the peak voltage in 7 frequency bands. These voltages are multiplexed on one output pin. The timing is shown below, and includes some corrections compared to the datasheet Maxfield.

To read each value, we use the RESET and STROBE* pins.

• A RESET pulse followed by a wait (≥72 μs) resets the multiplexer.
• On the first falling edge of the strobe signal, the 63 Hz band output propagates to OUT. After ≥36 μs, this analog value can be read by the host.
• Each additional strobe falling edge advances the multiplexer one frequency band (63 » 160 » 400 » 1,000 » 2,500 » 6,250 » 16,000 Hz) and this will repeat indefinitely.

Each read operation decays the value of that frequency band by approximately 10%. This means that if the Arduino reads less often, e.g. as a result of doing computations, the values read will be higher.