Mixed voltage interfacing with the Bus Pirate

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This will be an updated guide to using the Bus Pirate pull-up resistors to interface stuff at different voltages.



The Bus Pirate's on-board pull-up resistors can be used to interface electronics above and below the Bus Pirate's 3.3volt supply.

Read how the pull-up resistors on the Bus Pirate work.

Read our guide to pull-up resistors and high impedance pins.


Here's some examples of how to interface different voltages using the Bus Pirate.

These examples assume you use the Bus Pirate on-board pullup resistors. If you use the Bus Pirate's on-board pull-up resistors, remember to connect the Vpullup pin to the circuit supply voltage. The Bus Pirate pull-up resistors are powered through the Vpullup pin.

Some modes (1-Wire, I2C) only use high impedance pin outputs


Select output type:
1. Open drain (H=Hi-Z, L=GND)
2. Normal (H=3.3V, L=GND)

(1)> 2

  • Interface directly with normal pin outputs
  • No pull-ups or Vpullup pin connection used


  • Choose Hi-Z output type
  • Connect the Vpullup pin to the power supply of the 5volt circuit
  • The 5volts can come from the Bus Pirate or an external supply


  • Choose Hi-Z output type
  • Connect the Vpullup pin to the power supply of the 2.5volt circuit

Any voltage 1-Wire, I2C

  • The Bus Pirate can interface with 1-Wire or I2C at 5.5volts or less
  • Open collector buses like 1-Wire and I2C always use pull-up resistors
  • These modes have no output configuration, outputs are always HiZ