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Problem with voltage readout

49 Views - Created 17 days ago

17 days ago

Posted by:
landelifestyle1

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Hello, 

I am working on a sensor which produces varying voltages with 5V power. I used another ADC and multimeter to give about 1.24V. However when using the ADCPi the readout is around 3.1V. I have not made any modifications on demo_readvoltage.py or ADCPi.py. Is there any conversions I have to make in the code?

I plugged into terminal + and - of all channels it seems to be giving same voltages. I have two ADC Differential Pis and tried on both they gave same numbers so I believe it is the code's problem. 

Please help. Thanks!

17 days ago

Posted by:
andrew

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Location:
United Kingdom

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Hello

With the ADC Differential Pi you will need to use the ADCDifferentialPi.py library instead of the ADCPi.py library. 

The ADCPi.py library is designed to work with our ADC Pi boards which have a voltage divider on the inputs.  The library multiplies the input value by 2.471 which is why your 1.24V is displaying as 3.1V.

AB Electronics UK Tech Support

17 days ago

Posted by:
landelifestyle1

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Thanks Andrew! May I ask what the ADCPi is for then? I do not  see a product that you have that is jusr ADC Pi.

17 days ago

Posted by:
andrew

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We have this ADC Pi board which is the almost the same as the ADC Differential Pi but with voltage dividers on the inputs to increase the voltage range.

AB Electronics UK Tech Support

14 days ago

Posted by:
landelifestyle1

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Thanks! I assume it is ok to stack up the ADC Pi and ADC Differential Pi. I know that the ADC Pi is single ended output, if I already have three ADC Differential Pis connected to sensors would noise be a big problem fro the ADC Pi? (I am trying to maintain the 0.05% accuracy)

14 days ago

Posted by:
andrew

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Location:
United Kingdom

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You can stack the ADC Pi and ADC Differential Pi on the same Raspberry Pi.  As they both use the same ADC chip you can only stack 4 boards in total so if you have three ADC Differential Pis you will be able to add one ADC Pi to the stack.

Each ADC chip has its own internal voltage reference which is accurate to 0.05% so you shouldn't have any issues using the ADC Pi and ADC Differential Pis together.

To get the best accuracy you will need to make sure your power supplies are stable as noise on the power lines could reduce the accuracy of the ADC inputs.

AB Electronics UK Tech Support

14 days ago

Posted by:
landelifestyle1

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Hi Andrew, Thanks for your reply! I am planning to put 4 ADCs together, that solves my problem. Thanks!

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