This website contains information on building and using home made 7 key chording keyboards.
I have been using this device or one of its predecessors since the mid 1980's, by 1995 it has been a full function chorder and my primary keyboard with both Herbert, my wearable computer and conventional desktop machines.1) Currently I use two versions, on the desktop I still use the pre-arduino spiffchorder which will work with any device that supports a USB keyboard, with wearables, phone and tablet I use the BLE featherchorder which works with any device that can take a BLE compliant keyboard. The Spiffchorder was made possible as a result of work done by Mikkel Holm Olsen on the SpiffChorder. If you are starting out you may find the featherchorder a better first project as it fewer parts to solder and does not require any other hardware to program it.
/!Some of the instructions found here involve using sharp tools and soldering irons. We make no claims as to the safety of such activities.!/
Each project lists contact information for the person who created or maintains it. Please use that information when inquiring about a particular project.