Replacement for the B2972 control card, used by the FX-951 and other Hakko soldering stations.
This version of the card is much lower profile than the original, so that it only sticks out of the station by a mm or so. I prefer this for aesthetics, and it's also less likely to get bumped accidentally. It's not very convenient if you actually use the key for its intended purpose (you need to tip the station or use your nails to get it out), but I assume most hobbyists leave it in permanently like I do.
The card must be solid enough to block the sensor light inside the station, so a dark material is strongly recommended.
The example in the photos was printed using JLCPCB's SLA resin service.
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The author marked this model as their own original creation.