what is the A0 input Voltage

Question

Hi could some one please clarify this issue,

I'm trying to do some simple Voltage readings with my ESP8266 AI_Thinker.

Reading the Infos on the web, the max input on ADC should be 1Volt.

When I supply 1V to A0 I get a ADC reading of 325

When I connect the 3.3V supply of the ESP directly to A0 I get a reading of 1010.

So, to me it seems that max input voltage is rather 3.3V and not 1V.

Please comment

thanks

Uli

Comments

The AI Thinker Schematic shows a Ext-voltage-220K-100K-Gnd voltage divider or 3.2 divider chain, so 3.3v input = 1.031 so subject to a small ADC error is what your getting 1010/1023 = 1.3% error

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Thank you, that explain it.
I tried to find a schematic of AI Thinker but without success. Where could I find one.
greetings
Uli

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There are many: http://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwiDxc_KvO7aAhXBUBQKHct_CosQjRx6BAgBEAU&url=http%3A%2F%2Fwww.wendangku.net%2Fdoc%2F638b48420b4c2e3f5627630c.html&psig=AOvVaw2ELN7PK2BKJUgyQi1ANJYM&ust=1525606325871871

Google ai-thinker schematic

Answer 1

Hi Uli,

Max input for the chip is 1 Volt, but many esp8266 boards have a voltage divider that translates A0 inputs in the 0-3.3V range to voltages in the 0-1V range for the chip. Your observation suggests that your board has one too.