This is a nice device, not too expensive for hobby.
For Senseair K30 CO2 sensor
The device works fine. So far I've only tested the analog output connected to Arduino A/D converter. On my request, the seller was able to disable the automatic calibration as in my application the CO2 level never reaches 405 ppm and I have to do manual calibration outdoors. I blundered and reverse connected an external +5V power supply (idiot me). Amazingly, the unit still seems to work normally.
