And in another unpublished episode of “We won’t stop until a Raspberry Pi makes us a cappuccino,” the plan is to combine the magic of the popular mini computer with a terminal older than the one writing this text. After letting it sleep for a couple of years, user dennis1a4 took his Heathkit H-19A terminal from 1980, performed some repairs, and connected it to a Raspberry Pi through its serial interface. The final result is much more “Fallout” than we can imagine.
Terminals require a bit more patience than a traditional computer. Modern software can emulate the most well-known terminals to a large extent, but if you plan to restore or reuse one, you should know very well what you are doing. My general knowledge is limited to terminal keyboards, converting their protocols and the modifications they need to work properly on a current system. However, some enthusiasts out there have the time and skill to go further. A good example is dennis1a4, who rescued a Heathkit H-19A terminal (August 1980) from the trash. Several years later, he decided to take it off his shelf and do something with it. The best option? Use it as a terminal for a Raspberry Pi.
Being a piece of hardware with more than three decades of age, it is logical to expect some technical problems. In this case, the -5 and -12 volt lines were out of action. The 7912 regulator (-12v) is responsible for powering the 7905 (-5v), so the first suspicions focused on the 7912, but its operation out of circuit was correct. When measuring the -12v line, he discovered a short to ground at some point. Fortunately, the first component he removed turned out to be the culprit, an old capacitor at the output of the 7912. Once the capacitor was replaced and the regulator reinstalled, he began working on the rest of the terminal. There was echo of characters but nothing on the output, because it was in offline mode (the key that changed the mode was broken).
And so we arrive at a voltage conflict. The Heathkit H-19A uses +/-12v on the serial interface, with the potential to light up the Raspberry Pi like a Christmas tree. Once again, luck favored dennis1a4: The voltage on the data line from the CPU to the serial interface chips was about 3 volts, therefore, the solution was to remove those chips, and connect the Raspberry Pi directly to the terminal's CPU. The last step was to enable ANSI escape sequences, and configure the link at 9,600 baud. The rest is history.
