HW

Hardware - Overview

One part of the project is the hardware to adapt the current loop for TW39 to modern logic level ports. The 5V or 3.3V TTL lines can be connected directly to an USB-serial-adapter or the GPIO pins of a Raspberry Pi. The current loop is designed as an analog 40mA current regulator in combination with the switching transistor.

As side effect teletypes with V.10 interface (like TeKaDe FS200Z / FS220Z) can also be connected to a USB-to-RS232-adapter with a simple DIY adapter cable. The V.10 interface control lines are completely handled by the software (No FAG200 is needed).

Another playground is the ED1000 interface used by (more) modern teletypes (like Siemens T1000, T1200 or SEL Lo2000, Lo3000). It is based on frequency-shift-keying (FSK) and is handled by a USB sound card, a few passive components and a lot of software.

piTelex tries to minimize the hardware efforts. The following sections describe various proposals for connecting teletypes to a contemporary PC or a SBC with minimal requirements. Other proposals are welcome, be it alternative circuits or extensions to the basic functionality.

Hardware requirements

If your teletype equipment runs TW39 or V.10 protocol, a Raspberry Pi Zero W or equivalent is more than sufficient to control these devices. For ED1000 you should better look for something like a Pi 3b+ or Pi 4, because the needed FSK computation needs more ressources.

If you want to run piTelex on a PC (linux or Windows), any contemporary computer equipped with an USB terminal will do. But take into account that for more fine grained device control you will need the support of digital I/O-lines of a RaspBerry Pi.

Interface hardware

In addition to the computing device you will have to prepare some interface hardware depending on the protocol your TTY hardware uses. Possible schematics are proposed in the corresponding sections. Feel free to adapt them to your needs.

For those who prefer to have ready-made PCB's there is a supplemental project piTelex.supplement where they can find many ressources for the hardware part of the project.

Examples

The section about built examples shows the flexibility of piTelex concerning hardware interfaces and also gives some hints for a succesful interaction of the hard- and software components.

If you have developed alternative or additional hardware circuits, PCB's or anything else that you want to share in the context of piTelex: Feel free to contact the developers!