A couple of years ago I built a programming interface for my Yaesu VX-6R handheld radio based on the CATbox circuit created by G4TIC. I have been using the interface with the excellent VX-6 Commander from Jim Mitchell (KC8UNJ). Even at the time I no longer had a computer with an RS232 serial port and although the interface worked it was never reliable using USB to RS232 converter cables.
I have recently been playing with the FT232RL USB to TTL serial chip on a number of other projects. It occurred to me that this would make the basis for a much more reliable interface to the VX-6. In order to make it easier to use the FT232 SMD chip I have been using a breakout board from Sparkfun Electronics (available from Little Bird Electronics in Australia) which contains all the support circuitry to get the FT232RL working, including TX and RX LEDs.
Before embarking on building an interface based on the FT232RL, I returned to Jim Mitchell’s site and checked out the page on interface cables where I found a USB design from Alexander Meier (DG6RBP) which uses an older chip from the same manufacturer as the FT232RL. I quickly breadboarded an interface using the buffer circuit from Alexander’s circuit, the section of the circuit consisting of four transistors and seven resistors connected to TX/RX on the older FT232BM chip, and the FT232RL Sparkfun breakout board. Much to my surprise and delight it worked first time, a refreshing change from the previous interface I built.
Having proved that the circuit would work, I then moved on to consider how I could build a permanent interface based on the FT232RL. After some consideration it occurred to me that it made sense to simply integrate the buffering circuit with the breakout board. Using protoboard, I built a circuit consisting of the transistor buffering (I used the generic PN100 NPN transistor) and two headers into which the Sparkfun breakout board can be plugged.
The board has a four pin header which connects to the radio. The header consists of data out, data in and ground. However, for the VX-6R the data in and data out are connected and I only use two wires to connect to the radio. If I want to use the interface with a radio that requires separate data lines I can remove the solder bridge connecting them.
The resulting board and FT232RL combination is extremely compact and works flawlessly every time (so far at least). I have the added benefit of being able to unplug the FT232RL breakout board and use it to connect with other devices and projects.