[ESP8266 - AdcRead()]: Read ADC delivers max. value of 1024 instead 1023 - BUG?

[hasenradball]

Basic Infos

• [x ] This issue complies with the issue POLICY doc.
• [x ] I have read the documentation at readthedocs and the issue is not addressed there.
• [x ] I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• [x ] I have filled out all fields below.

Platform

• Hardware: ESP-12
• Core Version: 2.5.0
• Development Env: Arduino IDE 1.8.9
• Operating System: Windows/Ubuntu

Settings in IDE

• Module: Wemos D1 mini / Nodemcu
• Flash Mode: dio
• Flash Size: 4MB
• lwip Variant: not known
• Reset Method: nodemcu
• Flash Frequency: 40Mhz
• CPU Frequency: 80Mhz
• Upload Using: SERIAL
• Upload Speed: 115200

Problem Description

If i read the adc pin on the ESP8266 or the Wemos D1 mini I get a max. value of 1024.
But the documentation says it ist a 10-bit adc with a range of 0...1023!
Why do the AdcRead() function deliver 1024!!??

Is this problem known?

[5chufti]

to signal overflow?

[hasenradball]

Means if creater than 1 V at the adc delivers 1024?
I dont believe.

[TD-er]

Does the AdcRead() function return the output of the ADC, or does it apply some calibration or maybe uses a lookup table?

[hasenradball]

It is the direct output of AdcRead()

[TD-er]

@hasenradball I get that, but what does that function return?
Is it the direct output of the ADC, or is it doing something in software on that data?

[devyte]

Our adc read function is a thin wrapper around the SDK function. I suspect inside the SDK there is a filter of some kind, i. e. it measures several times and calculates the result to return. If that SDK function returns 1024, there is nothing we can do.
There is a fast read function in the SDK, take a look at document 2c NONOS API reference from Espressif.
Closing for now.

[hasenradball]

Hi,
thank you!
Ok understood the resolution of the function system_adc_read() is 1/1024.
There was some misunderstanding.
Is the function system_adc_read_fast() availabe in the core 2.5.0?

[d-a-v]

It is available in the firmware. If it is usable/working it could be wrapped in the ESP:: class.
The FW documentation states WiFi must be disabled when using it.

[hasenradball]

Hi,
I also would like to use the following function to measure the vdd33.

How can I do to make it available in the ESP class?
Can you give me some hint how to manage this and which steps I have to do?

[d-a-v]

You just need to declare the function in your sketch, and try it. If it works we can encapsulate it later.

extern "C" void system_adc_read_fast (uint16_t* adc_addr, uint16_t adc_num, uint8+t adc_clk_div);

[JAndrassy]

@hasenradball To read VCC voltage, use ESP.getVcc(). but read the doc first: https://arduino-esp8266.readthedocs.io/en/latest/reference.html#analog-input

[hasenradball]

@JAndrassy Thanks I tested it.
I get Read Vcc: 3061.
Is the unit in mV?
Do you know?

[hasenradball]

Hi Is this right in this way?
Running on an ESP8266-01.
I would have expected Values between 0...1024?!?

[5chufti]

as you posted yourself 5 comments above, the unit is 1/1024V, giving 3,44 V in your example