TomS-Uk
Posts: 5
Joined: Sun Jun 10, 2018 7:35 pm

Wiring multiple i2c together

Sun Jun 10, 2018 7:50 pm

Hi all

I’m a regular forum viewer but this is my first post.
I’m building a sensor device and have wired 4 i2c devices together. I have wired from one SCL pin to another, sort of daisy chaining them together. The same for SDa Vin and Gnd. However none are detected on my pi.
I’m a novice when it comes to electronics and I’m learning as I go.
Should this setup work?

Thanks
Tom

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joan
Posts: 15003
Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: Wiring multiple i2c together

Sun Jun 10, 2018 9:23 pm

No reason it shouldn't work.

For safety all your devices should be 3V3.

Could you show either a photo of your connections or a detailed schematic?

TomS-Uk
Posts: 5
Joined: Sun Jun 10, 2018 7:35 pm

Re: Wiring multiple i2c together

Mon Jun 11, 2018 11:19 am

Thanks for the reply

I can't upload the image as it's saying it's too large but here is the link
https://1drv.ms/u/s!ArKqRmWga3sHgYJUO0MkuBSqeWkd5g

I plan on doing some testing with it tonight I just wondered if I've even wired it correctly

Thanks
Tom

Bruce_Pi
Posts: 20
Joined: Tue Feb 21, 2017 5:09 pm

Re: Wiring multiple i2c together

Mon Jun 11, 2018 5:25 pm

did you check the pull ups ?
I2C wont work untill you pull SDA and SCL lines high. A 4.7K will be a good choice.

TomS-Uk
Posts: 5
Joined: Sun Jun 10, 2018 7:35 pm

Re: Wiring multiple i2c together

Mon Jun 11, 2018 9:54 pm

I sorted it. I de-soldered the connection to my Pi and tested them on a breadboard. They work fine in that configuration so I must have had a dodgy solder joint or something :lol:

TomS-Uk
Posts: 5
Joined: Sun Jun 10, 2018 7:35 pm

Re: Wiring multiple i2c together

Mon Jun 11, 2018 9:55 pm

Bruce_Pi wrote:
Mon Jun 11, 2018 5:25 pm
did you check the pull ups ?
I2C wont work untill you pull SDA and SCL lines high. A 4.7K will be a good choice.
They work without any resistors? I thought a pi has pull ups built in?

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joan
Posts: 15003
Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: Wiring multiple i2c together

Mon Jun 11, 2018 10:06 pm

TomS-Uk wrote:
Mon Jun 11, 2018 9:55 pm
Bruce_Pi wrote:
Mon Jun 11, 2018 5:25 pm
did you check the pull ups ?
I2C wont work untill you pull SDA and SCL lines high. A 4.7K will be a good choice.
They work without any resistors? I thought a pi has pull ups built in?
Yes, the Pi has 1k8 resistors between GPIO 2/3 and 3V3 specifically for I2C.

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