Given how well PAPERS0 worked, and that we had a pretty good idea of what kind of electrical surprises to expect from the printer ports, we decided to design and build a simplified version that would use only TTL parts -- no PALs. This unit used just 8 standard TTL chips to implement a non-partitionable static barrier version of PAPERS0.
Aside from the logic simplification, the TTL_PAPERS unit incorporated a few improvements. An obvious change is that the front panel has just one LED for each PE and one LED that acts as a power indicator. This brought the power consumption down to a level that allowed us to use a cheap AC wall adapter unit, a few capacitors, and a 7805 voltage regulator as the power supply. We also simplified construction, reduced signal noise, and cut cost by directly connecting cables to the circuit board rather than connecting them to a rear-mounted connector that is in turn connected to the circuit board. Because the cable mounts and power supply no longer mandated a large box, we were able to make the box much smaller, and changed to a design that used a pivoting "hood" for the cover. Another change was that all connections were soldered rather than wire-wrapped, greatly improving reliability.
For all you woodworkers out there, the TTL_PAPERS box is Oak with a cover made out of Poplar.
The only thing set in stone is our name.