[2024-feb-29] Sad news: Eric Layton aka Nocturnal Slacker aka vtel57 passed away on Feb 26th, shortly after hospitalization. He was one of our Wiki's most prominent admins. He will be missed.
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| howtos:hardware:arm:interfacing_i2c_devices [2023/05/28 12:39 (UTC)] – [Detecting Connected Devices] louigi600 | howtos:hardware:arm:interfacing_i2c_devices [2023/05/28 13:16 (UTC)] – [Voltage Level Shifting] louigi600 |
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| ====== Preface ====== | ====== Preface ====== |
| Most modern PC have several internal components that communicate vital information, like internal temperatures of critical components, over I2C bus. This type of stuff is factory wired into your PC and can be dealt with lm_senosts ... what we want to do here is use an I2C bus on your computer to connect some external I2C sensor like an accelerometer. I'm tagging this in the ARM hardware section because I think that, excluding the lm-sensors stuff, most people will be doing this sort of thing on embedded ARM systems ... but the concepts are applicable to any linux capable system with an I2C bus. | Most modern PC have several internal components that communicate vital information, like internal temperatures of critical components, over I2C bus. This type of stuff is factory wired into your PC and is normally dealt with lm_senosrs ... what we want to do here is use an I2C bus on your computer to connect some external I2C sensor like an accelerometer. I'm tagging this in the ARM hardware section because I think that, excluding the lm-sensors stuff, most people will be doing this sort of thing on embedded ARM systems ... but the concepts are applicable to any linux capable system with an I2C bus. |
| | Should you want to hack one of the many I2C busses on your PC the easiest one to access is the one in the DIMM modules. Modern DIMM modules have an I2C eprom in them that the bios reads to find out the characteristics of the DIMM module. Since the DIMM module can be removed from PC and hacked separately without risking to damage permanently your PC it is probably your safest option. |
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| ====== Preparing Your Host System ====== | ====== Preparing Your Host System ====== |
| This is how I connected my 5v IMU pcb to a 3.3v I2C bus on my RaspberryPI: I took as educated guess that 4.4v (5v with a 4148 diode in series) would still be a tolerable power supply voltage for the whole IMU pcb, this would most likely allow all the I2C devices on the IMU pcb to recognize a minimum of 3.08v (4.4 * 0.7) as the lowest reliable logic level 1 tension allowing it to inter-operate with the PI's 3.3v logic levels. I was not able to find if the PI has internal pullups on the I2C bus or if they have to be externally placed so in doubt I put in 10k pullups between the 4.4v power line and the 2 data lines. I was the able to correctly detect the sensors on the IMU pcb. | This is how I connected my 5v IMU pcb to a 3.3v I2C bus on my RaspberryPI: I took as educated guess that 4.4v (5v with a 4148 diode in series) would still be a tolerable power supply voltage for the whole IMU pcb, this would most likely allow all the I2C devices on the IMU pcb to recognize a minimum of 3.08v (4.4 * 0.7) as the lowest reliable logic level 1 tension allowing it to inter-operate with the PI's 3.3v logic levels. I was not able to find if the PI has internal pullups on the I2C bus or if they have to be externally placed so in doubt I put in 10k pullups between the 4.4v power line and the 2 data lines. I was the able to correctly detect the sensors on the IMU pcb. |
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| | ====== Hacking I2C in DIMM modules ====== |
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| ====== Sources ====== | ====== Sources ====== |
| <!-- If you are copying information from another source, then specify that source --> | <!-- If you are copying information from another source, then specify that source --> |
