I bought two Chirp plant watering alarms and I noticed that the attiny44a used are marked differently: atmel1722 and atmel1619.

What is the meaning of the numbers? I cannot find this information in the datasheet.

Are they some sort of serial number or batch?

enter image description here

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    \$\begingroup\$ Yep. \$\endgroup\$ – Maple Jun 12 '18 at 11:36
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    \$\begingroup\$ Also, note that the silkscreens on both boards are different, too. Not only in the font they use! One says v.1.1, the other V1.1. Someone took the board layout, and modified it slightly, and then made new gerbers, but they didn't change the version string – bad idea (don't do something that's different but has the same version and name - otherwise, versioning makes no sense). \$\endgroup\$ – Marcus Müller Jun 12 '18 at 12:29
  • \$\begingroup\$ @MarcusMüller come on, it's made in China copying a design from someone else :) I could have shown you the bottom part of the one on the left, where the opposite arrow overlaps the text! But they work fine and they cost less than 3 dollars, so... \$\endgroup\$ – FarO Jun 14 '18 at 20:00

Those are date codes: They represent the 22nd week of 2017 and 19th week of 2016, respectively.

(Thanks to Maple for the link.)

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