MCU

Hello everyone, I am a rookie who just started, and I encountered a problem on the project a few days ago. To put it simply, I use ads1115 to measure the input voltage value, the voltage value is 12V, and I use 10k/20k to reduce it to one-third of the measurement. However, during the test, it was found that the measured value would fluctuate and could not return to normal conditions. For example, the voltage value is 10v at this time, and it is about 3.3 after three equal divisions. This is a normal situation, but it may jump to 4v, 2v, and this situation is not a problem with the reading. Use a multimeter to measure the input terminal and read it with ads1115 The values are the same. The strangest thing is that I removed the resistor and measured its value, but it changed. The 10k resistance became 9.5k, 9.7k and gradually increased. This situation has also occurred with the uno board of arduino before, but it did not solve it, so I changed it to 1115 and tried it. I didn't expect this problem to occur again. In addition, this situation does not necessarily happen.

Please give me a solution or idea.

Nayeli Posted on September 18, 2020

Have you considered this? ? The internal resistance of the voltage source that you get after the voltage division of 10k and 20k is theoretically 10k//20k, but under normal circumstances, the internal resistance of a voltage source should be infinitely small. You look at the manual ads1115 input impedance? ? So can the output voltage be 1/3vin? ? Therefore, the output cannot be stabilized. You connect a voltage follower at the two resistor divider points to reduce the output impedance, then the voltage measured by the ads1115 should be stable.

As for the resistance value of the 10k resistor you mentioned, I think it is normal. Maybe the multimeter is interfered. There is electromagnetic interference everywhere in the environment, and the resistance will also contain a certain amount of capacitive and inductive electricity, so there will be resistance fluctuations. normal,

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Itzel Posted on September 18, 2020

This is absolutely impossible for you, the 10k resistance has become 9.5k, 9.7k and gradually increase, are you sure it is not a problem with the meter?

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Skyla Posted on September 18, 2020

"Use a multimeter to measure the input terminal, and it is consistent with the value read by ads1115" When you use the multimeter to measure, is the resistance divider terminal connected to the ADC input terminal? ? ?

I think your resistor divider ground and ADC ground are not the same ground, how do you deal with it? . .

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