The TTY-Connect circuitry is comprised of several independent sections, and can be built with only
the sections that suit your needs.
HV1 (High-Voltage TTY Loop 1) has an 80VDC (or 160VDC) loop supply, 60-mA (or 20-mA) current limiting, two insulated 1/4" jacks for TTYs (M14, M15, M19, M20, M26, M28, M31...), and full opto-isolation for data in and out. A switch configures the two jacks for full- or half-duplex mode. In full-duplex mode, one jack is an input loop (HV1-IN, for keyboard/td-contacts) and the other jack is an output loop (HV1-OUT, for typing-unit/reperf selector magnets). In half-duplex mode, the jacks are connected in series for a local loop of keyboard/td-contacts and/or selector magnets.
HV2 (High-Voltage TTY Loop 2) is identical to HV1.
LV (Low-Voltage TTY Loop) has a 25VDC loop supply, 20-mA current limiting, two insulated 3.5mm (1/8") jacks for TTYs (M32, M33...), and full opto-isolation. A full/half-duplex switch is also provided.
PC232 is an RS-232 interface for connecting to a PC. A DB9-F jack allows a PC serial port to control the TTY-Connect system, and connect to TTYs. The PC232 signals are available for either driving an optional on-board microcontroller, or for patching directly to one of the opto-isolated TTY loops. If the PC232 port is patched directly to a loop, the PC program must be able to send the correct word format required by the TTYs (eg: 5-bit, 60-wpm baudot). The DTR and RTS signals on the PC232 jack are buffered and available on the AUX jack, and may be used for radio keying, or other functions, if activated by the PC.
TU232 is an RS-232 interface for connecting to a Radio/Terminal-Unit. A 6P6C modular jack allows connection of a TU (Terminal Unit) for receive and/or transmit use. The signals are available for either driving an optional on-board microcontroller, or for patching directly to one of the opto-isolated TTY loops. If the TU232 port is patched directly to a loop, the TTYs must be able to receive the correct word format received by the radio/TU (eg: 5-bit, 75-wpm baudot). This interface is for standard RS-232 signals (mark < -3V, space > +3V). If the optional PIC microcontroller is installed, there is a software inversion available for connecting to a TU with MIL-188 signals (mark = +5V, space = -5V). If the optional micro is installed, there is also a push-to-talk (PTT) signal available on the TU232 jack, for keying a transmitter.
The Optional PIC microcontroller may be used to provide data-regeneration, programmable signal connections between the loops/TU/PC, and customizable features like Auto-CR-LF-Insertion, Autostart (motor powering), Selective-Calling, Who-Are-You (WRU), Ascii/Baudot-Conversion, Speed-Conversion, etc. Firmware in the PIC may be updated via the PC232 port, using a small downloader application that runs on a windows PC. If the PIC is not installed, fixed patching of the TU232 and PC232 ports directly to the tty loops may be performed at the INTERCONNECT header.
Depending on the sections included, the unit can be built for about $70 to $130, including all chassis-mount transformers, but not including the chassis parts. You can also build it for less if you jumper out switches, don't build all sections, mount it in an old beer keg, etc. The board is 9.6 x 2.9 inches, and the parts fit easily into a 2U rack chassis that is 7" deep.