Wednesday, April 30, 2014

LPC812 Devl - 20 March 2014

The LPC812 MCU board in the picture plugs into, communicates with, and is powered by a USB port. It has 8 parallel port pins which can also be assigned to other functions. And opposite the USB port connector it has our standard RJ11 I2C bus connector.

You can find the document package for the board at: LPC812 Devl 20 March 2014 The board is available from OSH Park - LPC812 Devl - 20 March 2014 for $7.35.

Forth for the LPC812 is available at New FISH - LPC812 Support. There is a link to instructions on how to load the Forth into the chip at the link.

The NXP Users Manual can be found at LPC812 User's Manual.

Update: 25 June 2014 1419z

There is a problem with the 20 March 2014 version of this board. It was accepting spurious (real?) shutdown signals from the PC after about 10 days and would not power up. This happened on PCs with XP and Win 7 so it is not a specific OS problem. So it took about 30 days for me to be convinced it was a real problem. I had to see the problem twice and then investigate for about 10 days.

I designed a modified board that can be "wired" (resistor removed or added) to not respond to the shut down signal - the way everyone else does it. R17 and C22 have been added. R17 is normally NI (not installed). That disconnects the shutdown signal. As far as I can tell no one uses that signal to control power from the USB port.

You can find the documentation for this revision at LPC812 Devl 5 June 2014 - Doc. This board will be available from OSH Park for $7.33.

Further update: 24 July 2014

Upon further investigation it turns out that the difficulties I has were caused by an intermittent solder joint. And it was a very strange intermittent that worked for 10 days and then got flaky. And it did that twice. So you can use either board depending on what you like. Check the different schematics and make your choice.

Engineering is the art of making what you want from what you can get at a profit.

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