ESP8266 Community Forum

- Thu Mar 15, 2018 11:39 am #74628 Hello!
I'm a complete newbie, so I'm sorry if this is the wrong section for this.
I need to make a fixed data logger for 2 pyranometers and transmit this data to a web portal. A friend told me the ESP8266 is the best way to do this but I don't really know where to start.
The pyranometers have a sensitivity of 10 microvolts/ solar irradiance unit, so I know I'll need to amplify the signal but, again, I'm a newbie so I don't know what I need to do exactly!

Any advice is welcome! Thank you!

- Fri Mar 16, 2018 11:46 pm #74651 There are a number of different ways this can be done. But it has to be compatible with the server you want to send the information to. Without more information about the webserver, and what it is expecting, it is hard to guide you.

- Sat Mar 17, 2018 6:37 am #74656 For the front end conditioning one would normally aim for a full scale of 1000w/m2 which would be 10mV from your sensor.

The esp8266 has a single ADC with basic sensitivity of 1V full scale so you would need a dc pre-amplifier with a gain of 100. Note some ESP modules already have a 3.3:1 divider built in giving a full scale of 3.3V. I would use one without this so the pre-amp only needs to give 1V out.

A simple non-inverting pre-amp with a 100:1 feedback would do the trick. If one chooses an op-amp with a input range that covers 0V then that can be done with a simple single rail design.

You also want the op-amp to have low offset voltage and particularly low offset voltage drift with temperature. The initial offset can be calibrated out in the software. Something like an OPA317 (90uV offset / 0.05uV/C) would be a reasonable choice.

Note that the ADC in the ESP8266 is 10 bit precision but the initial 1V accuracy is not very good so you would want to calibrate for that.