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Topic: Altering the voltage on a BP 3 (Read 2108 times) previous topic - next topic

Altering the voltage on a BP 3

Hello All

This is my first post and I am a newbie to BP and using I2C. I have not received my BP 3 yet but would like to know if you can adjust the voltage below 3volts. The reason is I have a circuit board with a 3volt battery soldered onto it and run into these boards all the time, so would like to I2C them rather than de-soldering the battery.
My question is, can I lower the voltage to below 3 volts on the BP so as to be able to read the Eeprom, as to read the Eeprom the  max voltage is 5.5v. If I set the voltage to 2 volts on the BP and incorporate the board voltage of 3 volts would the BP be able to communicate with the eeprom.

Many thanks.

Re: Altering the voltage on a BP 3

Reply #1
Yes, I2C already requires pullup resistors so you need to follow this guide: ... Bus_Pirate

No, BP will not work with 2 V, at least I wouldn't use it there as brown out reset voltage can be 2.2 V. Also it requires you to change the voltage regulator, interface with FTDI IC will be kinda problematic.

Hidden in the microcontroller datasheet, we see that Input High Voltage is between 0.8 Vdd and Vdd, Supply voltage is 3.3 V so you need 2.64 V at least to be detected as high. Another option is to use level converter ICs or devices in between. For I2C you need bidirectional, so something like this should do:

Re: Altering the voltage on a BP 3

Reply #2
Hi Tayken

Thanks for the info on the logic level converter. I've just ordered one so will let you know how I get on.

Thanks again!