ADC voltage range

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kwiley
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ADC voltage range

Post by kwiley » Wed Jun 12, 2019 2:52 am

I'm considering hacking the ESP-01S to access the ADC line. The voltage range for the ADC is 0-1.1V, not the full logic range of 3.3V. My question is whether providing 1.1-3.3V to the ADC line harms the chip or whether it merely saturates the ADC so that it returns 1023 (10 bits) for any voltage above 1.1V. Does anyone know the answer to this question?

I need to figure out how to create a voltage divider to solve this problem, but I'm curious if the problem is merely one of signal saturation, or more seriously one of chip damage.

Thanks.

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Roberthh
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Re: ADC voltage range

Post by Roberthh » Wed Jun 12, 2019 6:50 am

A suitable voltage divider consist of just two resistors in the ratio 1:2.2, like 100kOhm and 220 kOhm. 100k between GND and ADC in, and 220k between ADC in and your new ADC input. You can add a small capacitor of about 1 nF between ADC in and GND too, parallel to the 100k resistor, which will reduce the noise.
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kwiley
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Re: ADC voltage range

Post by kwiley » Wed Jun 12, 2019 1:11 pm

Thank you. Still, I am curious about my original question. Does providing 1.1-3.3V into the analog sensor line merely saturate the signal so that it produces a 1023, or does it damage the chip?

Thanks again for the voltage divider design.

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Roberthh
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Re: ADC voltage range

Post by Roberthh » Wed Jun 12, 2019 3:45 pm

The answer to the first question is unclear. Having never fried an ESP8266 analog input and having seen not complaints from other users, the answer is: most likely it is not critical to apply 3.3V to the analog input.
You can find some comments in the net about the digital IOs of the ESP8266 being safe up to 5V, referencing a specific espressif manual. But that manual does not contain the cited statement.

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