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Thread: 3.3V Teensy and 5V MAX7219

  1. #1
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    3.3V Teensy and 5V MAX7219

    Hi,

    I have a simple question but I cannot find a satisfactory answer anywhere. Not even in this forum. My 3.3v teensy 3.0 is on the way and I would like to made a simple 8x8 matrix using MAX7219 which is a 5V device. Normally I would use a level shifter or MOSFET but in all example the MAX7219 seems to be connected directly to the Teensy. Does de MAX7219 work at 3.3V, even though the datasheets says different?

    None of the examples at pjrc.com, like https://www.pjrc.com/teensy/td_libs_Matrix.html, do mention the issue.

    Any experiences?
    Last edited by MasterMek; 02-25-2014 at 05:35 PM.

  2. #2
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    The examples on that page are using Teensy 2.0 which uses a 5V logic level. From the product page MAX7219 has a minimum supply voltage of 4V and max of 5.5V so it will need to be powered from 5V. The data sheet the Logic High Input Voltage is 3.5V. So you will need to use a level translator for interfacing.

    Something like this Adafruit 8-channel Bi-directional Logic Level Converter or this less expensive, but slower, 4-channel I2C-safe Bi-directional Logic Level Converter. Which to use depends on how many pins you need (remember to include one chip select pin per SPI device).
    Last edited by Nantonos; 02-26-2014 at 08:25 AM.

  3. #3
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    Thanks for the reply! I'll have a closer look.
    Also found this one, operating at 3-5V, using pwm control http://www.adafruit.com/products/1455...
    New approach.

  4. #4
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    MAX7219 should be really be powered with 5V (you can use Vbus if current doesn't exceed bus limits) but it will "understand" 3V logic signals from Teensy 3.x. Tested...

    But please don't take this for granted since datasheet really states 3.5V as miminum for recognising logic high.
    Last edited by rokjarc; 03-18-2014 at 05:13 PM.

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