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RE: SDA/SCL when stacking.

76 Views - Created 27 days ago

27 days ago

Posted by:
RTGibson

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Hi - I now have four ADC Pi's stacked on top of each other (but not stacked on the actual Raspberry Pi), I have the address jumpers as per the web site example 68/69 on the bottom board 6A/6B on the next board etc. I have only wired to SDA/SCL on the bottom board - thinking that the stacking would take care of connecting the other boards. When I do an i2cdetect though I can only see 68/69 - do I need to physically wire SDA/SCL to each board ?

Regards

Russ

27 days ago

Posted by:
andrew

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Location:
United Kingdom

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Hi Russ

The best way to wire the ADC boards will be to use the SDA (pin 3) and SCL (pin 5) pins on the GPIO header.  That way each I2C bus will be buffered through the voltage level translator on each ADC board and they should all show up with i2cdetect. 

You will also need to connect the 3.3V (pin 1), 5V (pin 2) and ground (pin 6) on the GPIO header to the Raspberry Pi.

AB Electronics UK Tech Support

26 days ago

Posted by:
RTGibson

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Hi - thanks for the response. I was going to try and post some pics but can't seem to do it. Rather than have the boards stacked on the Pi they are on a seperate board the SDA/SCL connections are on the bottom board (from pins 3 & 5) - there is a seperate 5v supply also connected to the bottom board. I can measure the 5V supply on all the other boards stacked on top so that seems to be OK but I'm not sure if the SDA/SCL pins are going all the way up the stack - they should do shouldn't they ?? I don't have 3.3v connected to any of the boards yet the bottom board is still detected with i2cdetect.

Thanks

Russ

 

25 days ago

Posted by:
andrew

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Hi Russ

Are you using the SDA and SCL on the ADC Pi on the boards GPIO connector or the two separate SDA and SCL pins?  The pins on the GPIO connector operate at 3V where as the separate ones are 5V so if you connect them to the Raspberry Pi they will feed 5V back into the Raspberry Pi GPIO header which could damage it.  I would recommend only using the pins on the GPIO header to connect to the Raspberry Pi.

The I2C voltage level shifter on the ADC Pi needs 5V and 3.3V to operate correctly so you will need to run a 3.3V wire to the ADC Pi as well for it to work.

AB Electronics UK Tech Support

25 days ago

Posted by:
RTGibson

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Hi Andrew - I was wiring to the two seperate SDA/SCL pins on the board not the GPIO header (eeeeeekkk).... fortunately my Pi seems to be alive. I'll move these to the header and wire a 3.3v to pin 1. Am I right in thinking I can just attach to the top header and it will pass through to the other boards below it ?

I'll do this over the next day or so and let you know if that solves the issue.

25 days ago

Posted by:
andrew

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United Kingdom

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Hi Russ

If you attach the wires to the top header then it will pass through to the other boards below it and they should all appear on the I2C bus.

AB Electronics UK Tech Support

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