[RTTY] TinyFSK modem for 45 and 75 baud

[Kok Chen]

For those who have not tried Arduinos before, they are single board Atmel AVR microprocessors which include their own bootloaders.  Arduino has a free program (runs on Windows and Mac OS) that combines its own C compiler with an uploader to program the chip (programs written this way are called "sketches.").  

http://arduino.cc/en/Guide/HomePage

The Nano model that Andy uses is the one that has the FTDI interface.  You can even buy Arduino Nano bootlegs that are made in the Far East at Amazon for less than half the price of the real ones (the cost of the real ones from Italy helps support arduino.cc's work on future Arduinos and desktop software).

Doug K4DSP had used a standalone Atmel AVR chip (ATtiny45) for the FSKit design, but that needed an in-system programmer if you want to program your own chip.  The Arduino that Andy uses comes with a bootloader, and all you need is a USB connection in your computer (and in the case of the Nano, an FTDI driver).

Other Arduino models (like the cheaper Arduino Micro, or the more capable Arduino UNO) use the USB CDC Class interface that requires no drivers, but they may not be compatible with the particular modem software that you are using, while FTDI is pretty much universal.  More advanced Arduinos have Ethernet and WiFi or Bluetooth interfaces, and you will definitely need to modify the modem software to use them :-).

If you use FSK, give Andy's TinyFSK a shot -- it will give you virtually perfectly timed bits (even to 75 baud) and with no funny stop bit lengths.  Note to the millisecond counters: you can easily lose 5 or 10 ms per character from stretched stop bits.

73
Chen, W7AY