[Barrow4491]

I have checked all connections (not that there are many) and all seem OK, and have tried with only the HTU21D and PMS7003 and still no result. I have even replaced the Nano with a new one.
I have a few observations which may give you a clue;
Input voltage measures 9.19v, regulator output 5.97v, the "L" led on the nano is constantly on, there is a regular red flash internally from the CO2 sensor and the fan in the PMS7003 never seems to move and i have not seen the Tx led flash.
I am at a loss!! 
Regards
JIm

Hi Jim

On my very first day of powering up the Air Quality board, I had similar results to what you mention above: A regular red glow from the CO2 sensor, LEDs illuminated on the Nano but nothing else worked. I would not get any flashing TX light or data upload.

My solution was I found that I had connected the quick connector pins around the wrong way on the PMS7003 at the sensor itself. When I unplugged and turned it around the correct way, everything came to life.

Not sure if this is the same situation as to what you are facing however. I attach a photo of the plug I got with my PMS7003 and you can see how easy it would be to get around the wrong way.

Hi,
Thanks for your input, but I realised early that the plug was reversible so I hunted the web for a data sheet to get a pinout of the sensor and the correct orientation is with the small pcb overhanging the sensor as the photo of your installation shows.
I am away for a month and will sort it out when I return (the regulator is faulty I am sure)
Regards
Jim