diff --git a/hardware/keyboard-sol/README.md b/hardware/keyboard-sol/README.md
index 9a70be3..87e03d2 100644
--- a/hardware/keyboard-sol/README.md
+++ b/hardware/keyboard-sol/README.md
@@ -2,6 +2,25 @@
 
 This keyboard replicates the keyboard on the SOL-20.
 
+This keyboad matrix works with one of the add-on ASCII encoders from this
+project, which must be separately built or acquired.
+
+This keyboard has a sibling [Sol-20 keyboard with integrated
+encoder][../keyboard-sol-integrated]. The two keyboards are identical except for the following difference:
+
+1. The integrated version places the connector closer to the main board keyboard
+   socket, so the original cable fits more easily.
+
+1. The non-integrated version requires a piggy-back encoder board. When
+   installing in a Sol-20, this piggyback board must be mounted on the right
+   side of the keyboard, and connected with a cable, to avoid mechanical
+   interference from the Sol main board.
+   
+1. The piggy-back encoder permits use with other machines, via the Apple-1 and
+   Apple-2 sockets, and two different user-configurable headers.
+   
+1. The piggy-back encoder also includes a UART interface.
+
 The keyboard is designed using KiCad in order to be the most useful for anybody
 wishing to modify the keyboard for more specific uses, or to add to the project.