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How to address two BMP388 on i2c
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How to address two BMP388 on i2c

by hotblack43 on Thu Jan 27, 2022 3:19 am

Hi,
I have two BMP388 sensors on boards from Adafruit. I want to read them both from the same i2c port on an Rpi. I put them in parallel. I run the detection code

i2cdetect -y 1

and I get the table that shows addresses. I see one address in use: '77'. This must be the 0x77 address that these sensors+boards are born with. So I figure I need to change the address of one of them ... I try the 'connect SDO and GND' trick, and sure enough the address changes to 0x76. Still only one shown, at the test, however.

So now I figure that because they are in parallel the changes in one is controlling the access to both - somehow. I also tried soldering the ADDR patches on the back of one of them. Same as above.

I must be missing something here - can anyone point me in the right direction, please? Either the sensors should not be in parallel, or they should be re-addressed in another way?

Thanks.

Peter

hotblack43
 
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Re: How to address two BMP388 on i2c

by dastels on Thu Jan 27, 2022 8:15 am

Can you post clear photos of the connections to the boards and the wiring as well as the i2cdetect output.

It sounds like you're doing everything right, but I'd like to see what you're doing.

Dave

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Re: How to address two BMP388 on i2c

by hotblack43 on Thu Jan 27, 2022 8:20 am

Thanks for reply! At the moment I have stopped trying the 'different adresses way' and am going "the multiplexer way" - but if that also does not work I shall be back here. Thanks!

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Re: How to address two BMP388 on i2c

by dastels on Thu Jan 27, 2022 1:39 pm

Grounding SDO on one board will set it's address to 0x76. ONLY VIN, SDA, SCL, and GND are connected in parallel. Notable NOT SDO.

There's no reason to use a multiplexer if you only need two of these sensors.

Dave

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Re: How to address two BMP388 on i2c

by hotblack43 on Thu Jan 27, 2022 3:50 pm

Thanks for that Dave, I put ALL pins in parallel- including SDO. Hah. Tomorrow will tell! Thanks. Peter

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Re: How to address two BMP388 on i2c

by dastels on Thu Jan 27, 2022 4:33 pm

It occurred to me that that's what might be happening. You were grounding both address pins, hence both switched to 0x76. Now you should be good to go... without the additional hardware & code that a multiplexor entails.

Dave

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Please be positive and constructive with your questions and comments.