[Aris] has quite a few MIDI devices that only have in and out ports. To chain together multiple devices, the MIDI slaves must have a “thru” port. Instead of daisy chaining, a better solution is to build a thru box to split the signal from the master. [Aris]’s thru box design uses an optocoupler on the input, which connected to 74HC14 hex inverting Schmitt trigger. The schematic shows three outputs, but there’s room for adding two more. A useful bit of kit for only a two hour job.