These type of sensors often have a warm-up time, often measured in minutes. The datasheet will tell you. If you don't let it warm up you will get poor readings.

@epierre said: I had the contact with this seller, but an international money transfer was needed and is expensive... yeah, they also have a minimum order quantity and ship with DHL only, so you have to pay import taxes to EU so it only makes sense if you order a big quantitiy and then try to resell it somehow all in all a hobby that at least has some return on investment, compared to other ones i had :)) You're courageous th have gone on kickstarter, from memory seeedstudio nearly went down because of an error on a crowdfunding project and had to produce and ship (the more expensive par of it) a remlacement for the first batches... ahh .. i didnt know this about them... and in their scale - i can undertand it happened to me as well but in my scale it was rather a paid lesson :))))

Go with the Z19. Here's some ready made code: https://forum.mysensors.org/topic/6528/mh-z19-co2-sensor/5