I built a K3NG keyer using an Arduino nano and it worked and fit fine as long as I didn't try the serial console feature.? It stores plenty of memories, has lots of options, you can use it for side tone, etc.??
But today I installed the KD1JV SKC keyer in my TS-440S.? It's tiny, simple, and works.? Two memories, variable speed, straight key mode, beacon mode, and it outputs audio to your rig's speaker to let you know where you are in the "menu".? Super simple.
Joshua
Joshua KJ7LVZ