Logic Level Shifter for 5V LCD to Teensy 4.0

[TonyAme]

Hello,
Thanks for reading. Would I need to use a logic level shifter to convert the 5V logic levels (I2C) of the LCD's scl/sda lines to 3.3V in order not to damage the Teensy's scl/sda pins? Any recommendations for an easy to use Level Shifter for this scenario?

Sincere Thanks,
TonyAm

 

[MichaelMeissner]

Hello,
Thanks for reading. Would I need to use a logic level shifter to convert the 5V logic levels (I2C) of the LCD's scl/sda lines to 3.3V in order not to damage the Teensy's scl/sda pins? Any recommendations for an easy to use Level Shifter for this scenario?

Sincere Thanks,
TonyAm

Generally yes. However, many i2c devices these days can run on either 3.3 volts or 5 volts. You might want check if your device can run at 3.3v and eliminate the level shifting.

In the past when I had devices that needed 5 volts, I would use one of the bi-directional level shifters:

• Pololu bi-directional level shifter
• Adafruit bi-directional level shifter
• Sparkfun bi-directional level shifter

To use them:

• In each of them, pick 2 out of 4 low voltage pins and hook pins 18 and 19 to it.
• On the other side, connect the corresponding high voltage pins to your devices scl and sda.
• Hook up 3.3v to the low voltage power pin.
• If you are powering your teensy with USB or your device can handle a wider range of voltages, hook up the Teensy VIN pin to the shifter's high voltage pin, and also connect it to VCC on your device.
• If your device is strict about 5 volts, and you are not powering the Teensy via USB (i.e. VIN might be 3.7 to 5.5 volts such as from a battery), I would suggest adding a 5 volt step-up/step-down voltage regulator between the Teensy's VIN pin and the high voltage power pin and device's VCC pin.
  • Depending on how many amps you need, I have used the Pololu step-up and step-down regulators such as:
    • Pololu S7V7F5 switching step-up/step-down regulator efficiently produces 5 V from input voltages between 2.7 V and 11.8 V, and can handle up to 1 amp of power
    • If your device is really power hungry, pololu has the Pololu S13V30F5, that can handle up to 3 amps and produce 5 volts.
    • If you need more than 0.5 amps, you will need an independent power supply rather than using VIN. This power supply would need to be connected to the level shifter high voltage power pin, possibly being regulated to 5 volts. However, the level shifters above, might not be able to handle high amps.
  • There are likely Adafruit and Sparkfun step-up/step-down voltage regulators, but I have tended to use the Pololu voltage regulator boards.
  • If you know your voltage is always going to be below 5 volts, you can use a step-up voltage regulator.
  • If you know your voltage is always going to be above 5 volts, you can use a step-down voltage regulator.
• On the Sparkfun and Adafruit boards hook up one of the Teensy ground pins to the ground pin on the low voltage side, and hook up the ground pin on the high voltage side to the GND or ground pin on your device.
• On the Pololu board, just hook one of the Teensy ground pins to your devices GND or ground pin. You can also do this for the Adafruit and Sparkfun boards, as I believe the ground pins are just directly connected.

Just to be clear, the above logic level shifters work fine for I2C devices. They likely will work with most SPI devices. But they are not fast enough to handle single directional LEDs like the WS2812B, SKC6812, neopixel, APA102, or dotstar products. These need faster converters like:

• Adafruit 74AHCT125 - Quad Level-Shifter (3V to 5V)