ESP8266 Community Forum

- Thu Jan 31, 2019 3:01 am #80351 Thanks again Rudy. I have ordered one so will give your suggestion a try.

Thanks

Lee.

- Thu Jan 31, 2019 4:06 am #80352 I was thinking about an external ADC yesterday as I assume it will consume less power than a voltage divider and my system is battery powered?

I can not find the link now but I read the measured voltage can't be 0.3V higher than the maximum voltage you are supplying on a ADS1015. I will see if I can find the reference later.

Just realised I sent quote to myself at work to discuss with an electronics person:

The PGA setting of +/- 6.144 range can be a little misleading as it seems to infer that you can measure voltages that high. You can’t.
Instead, the maximum measurable voltage is established by the supply voltage to the chip. Specifically, the maximum measurable voltage is 0.3 volts more than the supply voltage. In fact, exceeding this voltage at your analog input may damage your chip.
Note the differentiation here between the PGA range and the maximum measurable voltage. The programmed range determines the value of a bit (or scale factor), while the maximum measurable range determines what your analog input can safely handle.

- Thu Jan 31, 2019 4:11 am #80354 That's very interesting Gonzo. I had assumed I still needed the voltage divider. Any further info on which one you were looking at etc greatly appreciated. The one Rudy suggested seems to work between 2 and 5.5v

Thanks

Lee.

- Thu Jan 31, 2019 12:41 pm #80357 You would need a pull up resistor to Vcc (nominal 3.3v). The thermistor to ground. There is no other voltage divider. If a RC filter is used between the thermistor and the A/D pin, that will not affect the DC value.

If you are using the ESP8266 A/D then that will need a different arrangement due to the approximately 1 volt range.