9-DOF IMU - L3GD20H + LSM303 -> using a pull up resistor

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FMA
 
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9-DOF IMU - L3GD20H + LSM303 -> using a pull up resistor

Post by FMA »

Hi,

I'm interfacing a Raspberry Pi 3, running Raspian with a L3GD20H + LSM303 9-DOF IMU (currently discontinued), aiming for maximum possible performance in reading speeds.
The relevant part of my program is coded with C++.
I attempted configuring Raspbian to increase the I2C bus baud rate to 400kHz. The IMU on the other hand, it's related datasheets suggest that a pull up resistor must be used to achieve maximum I2C clock speed.

I'm not quite a pro in pull up resistors, but isn't there a built in one in the Raspberry Pi? Is it useful for my goal?
Any more information needed from my side?

Thanks!

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Re: 9-DOF IMU - L3GD20H + LSM303 -> using a pull up resistor

Post by adafruit_support_carter »

I'm not quite a pro in pull up resistors, but isn't there a built in one in the Raspberry Pi?
Yes, for the I2C lines on (BCM 2 and BCM 3):
https://pinout.xyz/pinout/pin3_gpio2#
Is it useful for my goal?
The pull ups are a requirement for I2C. They need to be incorporated on the bus somewhere. So they are useful for that. Otherwise you would have to add the resistors yourself externally.
Any more information needed from my side?
The value of the pull up resistors affects the achievable bus speed. Lower values are used for higher bus speeds. The ones built in to the Pi are 1.8kOhm. The sensor breakout also has pull resistors of 10kOhm. These are connected in parallel, so the overall pull up resistance is about 1.5kOhm (which should be OK for 400kHz).

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Re: 9-DOF IMU - L3GD20H + LSM303 -> using a pull up resistor

Post by FMA »

Thanks this was very helpful!

Since I increased the I2C baudrate in Raspbian, my time measurements for the readings did not show any improvement whatsoever.
Is there a better way to confirm that the new baudrate was indeed configured correctly?

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