Good JTAG on the cheap?

Several times I have used a tool called Universal Scan by Ricreations, http://www.ricreations.com available through Avnet Electronics Marketing as part number DS-KIT-USCAN. While an entry level tool, it was very useful in the laboratory for getting that first “it’s alive!” confirmation and debugging wiring issues, turning on LED’s for measurements, etc. It is unfortunately a bit expensive and high maintenance for the hobbyist/Maker market. I went searching for something open source and found something that might even be better… goJTAG.

On modern PC’s lacking a parallel port, goJTAG wants to have an FT2232H USB-serial for use with target boards. Unfortunately, the one they sell, picoTAP, is about $250, a bit steep considering the low cost eBay supply of its little brother, the FT232 used by Arduinos. A little searching on eBay turned up an FT2232H breakout board that has the JTAG populated, and available breakouts (supply your own pin headers) for the other serial ports. Link:

http://www.ebay.ca/itm/USB-to-Serial-UART-I2C-SPI-JTAG-Adapter-FT2232H-12-000-000-baud-/171247574639?pt=LH_DefaultDomain_2&hash=item27df269e6f&_uhb=1

These are sold by a user 100RandomTasks, of 100RandomTasks.com, 125 Eighth St, Midland, ON L4R 4A5 (Canada) for under $30. This was in my toy budget so I leapt on it.

I got around to plugging it in today and trying it with goJTAG software. Preliminary success! The device is seen and recognized. I have a bit more learning to do before I write up a how-to article, but this looks promising.

Link: http://www.digikey.com/product-detail/en/FT2232H%20MINI%20MODULE/768-1030-ND/2027252

It would appear that other variants are available based on the FTDI chip as well, from vendors such as Digikey and Seeedstudio.com. The module I got seems to be to have a better pinout for JTAG testing than the dual-row-header based FTDI reference designs.

FTDI is Future Technology Devices International Ltd, in case you were wondering!

For the software:

http://www.gojtag.com/downloads

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Fail of the day…

Well, it seems rechargeable CR123A-size (16340) Lithium batteries are higher voltage than SureFire (or other) primary (non-rechargeable) batteries, by quite a lot. Plop those bad boys in an old filament-style flashlight and POOF you get less than 100ms of light before burnout. Burned two just to be sure. 1200 mAh @ 3.7V nominal, fully charged at 4.19V. Guess I should have checked here: http://www.powerstream.com/cr123a-tests.htm

 

Those “3V” Lithium primaries are barely 3V when brand-new under no load. You get 2.5V for a while, 2V most of the time, and dead at 1.6V. V^2/R is a bit different from 4.2^2 and 2.5^2.

 

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During a lectur…

During a lecture the Oxford linguistic philosopher J. L. Austin made the claim that although a double negative in English implies a positive meaning, there is no language in which a double positive implies a negative. To which Morgenbesser responded in a dismissive tone, “Yeah, yeah.

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