While building my Minima CPU module, and thinking about the circuit's programming interface components. I started wondering if there was an Off-the-Shelf USB product that could replace and simplify the circuit.
After a little research, I found three likely candidates, all available from Parallax.com;
Each have slightly different header pin-outs for connection to a project. Each uses the same FT232RQ USB-to-Serial chip.
For DYI, the FT232RQ chip is a simple "state machine", which does all of the hard work of USB-to-Serial protocol and signal-level translation. It is simple enough that it could be included directly into a project, all that is necessary is; the FT232RQ, a USB connector, and a few resistors (see the Prop-Plug datasheet with schematic). Note: Parallax encourages use of their schematic for DYI implementation, they will be happy to supply the parts, or as available elsewhere.
If the FT232RQ is included directly in a project, the +5V from the USB connector could also be used by the project, only the off-the-shelf 4D Systems USB Programmer (listed above) provides a fifth pin for a power connection.
The FT232RQ is available in the 28-LD-SSOP and the QFN-32 package. I will use the QFN-32, because I like smaller components. The price of the FT232RQ is about $5.00, but that is cheap for what it does and the components that it replaces.
Also, if the FT232RQ is included directly as part of a project, it is available for generic ASCII I/O for control or output via a standard USB connection.
Because I already have a Prop-Plug, I think I will simplify and re-layout the next Revision of my Minima CPU module with a simple Prop-Plug header. I hope this will work as a generic dumb download interface with the Arduino Interactive Development Environmnet (IDE), but this remain to be tested. Does anyone know?
UPDATE: Apr 21, 2014 14:11
As per the comments, Larry has suggested the "FTDI Friend" - $15 from Adafruit.com