Input-Output Port Card
"Electronics - The Maplin Magazine"
Maplin Electronics
for TS1000 or ZX81 

* Adds Two 'bi-directional' ports for a total of 16 input or 16 output lines
* One buffered output port which can interface directly to CMOS
* On board address selecton allows for expansion to 6 ports with two PCBs
* Board assembled (Maplin Electronics Board) 

Expansion Board for up to 3 slots.
Required for attaching the I/O board to the computer.
Probably also a design published in "Electronics - The Maplin Magazine".