when the download cable is disconnected, which could
result in noise pickup that might interfere with program
execution. Their importance is clearly explained in PICAXE
If you want your download cable to be really small,
take a look at Jim Paris' FTXUSB serial breakout board
breakout-1/?pt=directsearch). At only 0.4" x 0.64" —
including a micro USB B connector — it's the smallest
cable currently being made. It uses a tiny FT230XQ chip
with RX and TX signals that you can invert with FTProg.
The cost is a little over $12 shipped, to which you must
add a USB micro cable and an output cable.
The next largest category is the CRIUS FTDI basic
breakout board from DealExtreme ( www.deal
extreme.com). At only $6.59 (including shipping), this high
quality FTDI board also doesn't need extra inverters. All
you would need to do would be to install input and
output cables and use FTProg to invert RX and TX.
Omega MCU Systems sells a board with an SI Labs
CP2103 chip and a couple of transistor inverters added
but it costs about $15 shipped, and you would still need
cables. It's also a little clunky.
You can buy a postage stamp-sized MCP2200
breakout board direct from the manufacturer (Microchip)
or from major electronics suppliers (Digi-Key, Mouser,
Newark, Farnell, etc.) for $15 plus shipping. Microchip
provides an EEPROM configuration utility that is similar to
FTProg that allows you to invert the RX and TX signals. All
you would need to add would be cables.
For the lowest cost download cable, you can use a
USB-to-TTL converter module based on a Prolific PL-
2303HX chip or an SI Labs CP-2102 or 2103 chip. These
are available from many sources in China, Taiwan, and
Hong Kong. Figure 3 shows some examples.
An easy way to recognize a board using a Prolific or
SI Labs chip is the 12 MHz crystal. (FTDI-based boards
■ FIGURE 3. Examples of Prolific and SI Labs USB modules.
■ FIGURE 4. Download
cable with transistor
32 July 2014