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arduino-interfaces

Code and wiring for interfaces between small, "Arduino"-like microprocessors

Controlling a 5V device with a 3.3V processor

e.g. Using an ESP32 to control a WS2812B LED strip

Use 74HCT125 (4-channel buffer/line-driver, individually-enabled) or 74HCT245 (8-channel transceiver)

IMPORTANT! Note the "T" in the name - 74HCT125 and 74HCT245 - this indicates that these chips use TTL-level input. Do not confuse them with their 74HC125 and 74HC245 equivalents which use CMOS-level input.

These chips are 5V CMOS devices but have TTL-compatible inputs. That means that they are supplied with 5V (at the VCC pin), and also output 5V (at the the Y(74HCT125) / B(74HCT245) pins), but they will interpret any input at >2.0V as a logical HIGH. This makes them ideal for receiving an input from a 3.3V MCU such as a Raspberry Pi or ESP8266/ESP32.

  • The 74HCT125 allows lines to be individually enabled, whereas all channels on the 74HCT245 are enabled/disabled fromna single OE pin.
  • The 74HCT125 is unidirectional - input on A pin always activates output on corresponding Y pin. The 74HCT245 allows transmission either from A to B, or from B to A (selectable via DIR pin))
  • Tie unused inputs to GND
  • As per 10. Power Supply Recommendations, place a 0.1μF and a 1μF capacitors in parallel across VCC and GND as close to the power pin as possible.

Feeding a 5V Input to a 3.3V device

Use a 74LVC1G125 logic level shifter https://www.diodes.com/assets/Datasheets/74LVC1G125.pdf