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i2cdetect not picking up both ADC chips

1388 Views - Created 14/04/2016

14/04/2016

Posted by:
ronny@thears.net

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Dear support team,

I'm using your ADCPi product for about a year and kept noticing that there is a problem with the detection of all applied ADC chips.

I'm using i2cdetect -y 1 to confirm. 

Sporadically one of the chips isn't responding anymore. It seemed to be triggered by a hard reset ( power down ).

I'm not sure if you are aware or have a solution / work-around available.

Thanks,

Ronny

14/04/2016

Posted by:
andrew

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Location:
United Kingdom

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Hi Ronny

When you do a hard reset are you disconnecting the 5V and ground pins or just the 5V?  We have found on our test rig that if you connect the ADC Pi 5V pin before the ground pin then for some reason one of the ADC chips will not be detected on the I2C bus.  This doesn't happen every time, probably one in every 500 boards and seems to be a bit random.  This is the first time we have heard about it happening to one of our boards out in the wild. 

The only thing I can think of is if the ground pin is not connected before 5V is applied then the power back feeds down the I2C pins instead of through ground and causes the ADC chip to stop responding.  It only ever does this on the second ADC U3 which by default has the address 0x69.  One of the address pins on this chip is floating so it could possibly be a problem that if the power isn't applied correctly the chip gets confused by the floating address pin.

One possible work around for this would be to set the address from 0x69 to 0x6A which would mean pulling the Adr 1 address pin high by connecting it to 5V.  If you look on our ADC Pi page it shows how to set different I2C addresses or use the image below.

Post image

If you don't have a spare jumper then you can just solder a bit of wire between the pins.

Hopefully by setting the address to be something other than floating it will stop the ADC from getting confused and will show the correct I2C address.

AB Electronics UK Tech Support

17/04/2016

Posted by:
ronny@thears.net

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Hi Andrew,

Thank you for your answer. 

I wasn't able to put a pattern on the problem yet. It's working great most the time but then it occurs again.

Is it possible to recover from the state without changing the jumper?

I appreciate your support,

Ronny

17/04/2016

Posted by:
andrew

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Location:
United Kingdom

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The only way we can normally get the ADC to reset to the correct address is to short the 5V and ground pins with a resistor to discharge the circuit completely.  I am not sure how you could do that with the ADC Pi connected to the Raspberry Pi other than by unplugging the power supply and leaving it for a short time to discharge before restarting it again.

AB Electronics UK Tech Support

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