Example_USB

Example with TW39 Compact USB Interface

TODO...

Hardware

This is the first approach with a USB to TTL adapter (middle), a DC/DC converter (bottom) and a self-made-board (top) for current regulator, reading and controlling the loop.

Schematics

This can be used with a Windows-PC, Linux-PC, Mac (not tested) and Raspberry Pi.

Version 2

The actual version uses the base PCB from the Raspberry Pi project part which is mounted in a lasered plywood case together with a DC/DC converter 5 to 30V and the CH340 board.

RTS/CTS Hack for TW39

To decode the TW39 protocol correctly, it is necessary to detect a permanent low and high level on the RXD pin. Neither the CH340 chip nor the drivers drivers can handle that. The hack is to use a separate input pin (CTS) to detect the state of the line.

Therefore the pin RXD has to be connected to pin CTS of the CH340 chip.

Most PCBs with the CH340 chip do not route the CTS pin to a connector. Use a thin wire to connect the pins 3 and 9 directly on the chip.

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Software

For Installation see SW_Install

This electronic is handled by the software module CH340TTY.

Start the program with arguments -W TTY on Linux:

telex.py -W /dev/ttyUSB0

or on Windows:

telex.py -W COM3

Adapt the com/tty port name to your PC/RPi setup.