The default I2C address is 0x74.

The IS31FL3731 has a lot of pins, and we wanted to make it easy to use with a breadboard while sandwiched with an LED matrix. The easiest way we could figure out to do this is make the board as large as our 0603-LED 16x9 matrix grids and have a control header on one edge. That way you can solder the two long headers directly to the matrix and still have access to pins for power and data.

Power Pins

You can power the IS31 from 2.7-5.5VDC, but note that the same voltage is used for both power and logic.

If you are using a 5V logic device, just connect VCC to 5V.

If you are using a 3.3V logic, you can either power with 3.3V, which will work fine for red, yellow or light green LEDs or you can power from 5V and then use ~2.2K resistors from SDA and SCL to 3.3V to 'overpower' the built in 20K pullup resistors.

I2C Data Pins

This chip uses I2C for control, it does not use clock stretching or repeated start. There are built in 20K pullups to VCC. You can run it as fast as 400KHz clock speed, but you may need to add additional 2K pullups from SDA and SCL up to VCC for higher speeds

  • SDA - I2C data line, connect to your microcontroller's I2C SDA pin.
  • SCL - I2C clock line, connect to your microcontroller's I2C SCL pin.
  • STEMMA QT (on the STEMMA QT version only) - These connectors allow you to connect to development boards with STEMMA QT connectors, or to other things, with various associated accessories.

Address Jumpers and Address Pin

  • Address Jumpers (0x75, 0x76, 0x77) - There are three address jumpers on the board, labeled 0x75, 0x76 and 0x77, below the I2C addr label on the board silk. This jumpers allows you to chain up to 4 of these boards on the same pair of I2C clock and data pins. To do so, you solder the jumper "closed" by connecting the two pads. The default I2C address is 0x74. To select a new address, solder the jumper labeled with the desired address closed. For example, to set the I2C address to 0x76, solder the 0x76 jumper.
  • ADDR - I2C address selection pin. The IS31FL3731 has a base 7-bit I2C address of 0x74 (1110100) and a clever addressing scheme that allows four different addresses using just one address pin (named ADDR for ADDRess). To program the address, connect the address pin as follows:

Other Control Pins

  • !SD or !SHUTD - Shutdown pin, default pulled up to VCC. Connect to ground to put the chip in shutdown mode.
  • AUD or AUDIO - Audio input, can be used to modulate the entire display with the amplitude of a line level audio signal. It has a series capacitor installed.
  • INTB - Output interrupt from chip when using the built in animation modes.

LED Grid

The LED Grid is much simpler, it just has 2 charlieplex grids, 16x9 total 0603 LEDs, with the two grids broken out to side pins that line up with the driver

This guide was first published on Mar 09, 2016. It was last updated on Jun 13, 2024.

This page (Pinouts) was last updated on Mar 08, 2024.

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