ESP8266 Community Forum

- Wed Nov 11, 2015 11:29 am #33706 Sorry for my bad english

So..I uploaded your sketch...
on "air" serial print me about 737, if I touch it about 740 and if I disconnect the A0 pin it send me 764.
Without Vcc it send me 727.

Tomorrow I try to use a tester to control voltage...
thank you!

- Thu Nov 12, 2015 6:43 pm #33808 hi,

LM35 operates from 4V to 30V. You can't use 3.3V. If you have VUSB pin on your NodeMCU board, use it, it's the 5V from USB port. Lolin boards have this pin. I don't know Amica. 'Offical' NodeMCU doesn't have this pin.

Then you need to convert the output of the LM35 to 0-1V range. You need a voltage divisor in theorie.
But LM35 with basic wiring give 0.01V/°C. If you don't go more than 100°C, you don't need voltage divisor.

(sorry if bad english, not my natural language)

- Thu Nov 12, 2015 8:20 pm #33812

LM35 operates from 4V to 30V. You can't use 3.3V. If you have VUSB pin on your NodeMCU board, use it, it's the 5V from USB port. Lolin boards have this pin. I don't know Amica. 'Offical' NodeMCU doesn't have this pin.

No need for an extra pin, "Vin" is connected directly to the 5V rail.

Then you need to convert the output of the LM35 to 0-1V range. You need a voltage divisor in theorie.
But LM35 with basic wiring give 0.01V/°C. If you don't go more than 100°C, you don't need voltage divisor.

And this is where you are screwed with the nodemcu devkit: there already is a 220k/100k voltage divider on the ADC input. So at 20°C you would only read 63mV on the ADC. I'm not sure how noisy the ESP's ADC is, but I suspect that there would be quite a bit of noise at that voltage level...

- Fri Nov 13, 2015 10:09 am #33858 Why bother trying to use a LM35 with ADC when there are several other temperature sensors which already communicate with a MCU digitally ?
For example, there are I2C sensors, such as the LM75, or even SA56004 which can also sense a remote diode, and there is also the famous OneWire Dallas DS18B20.