Thursday, September 29, 2016

KiCAD schematic symbols

Tonight I worked on the I/O-portion of the RPi HAT add-on board.
KiCAD didn't have schematic symbols for the 74HC244 Octal buffer/line driver and the MAX3483E RS-485 transceiver I want to use, so I spent the evening creating the two symbols in a library file.
The library is available at

Thursday, September 15, 2016

Two steps back, on step forward

It has been more than a year since I wrote about my efforts to create a print for the keypad. Since then I have mostly gone backwards...

I found out that soldering a 0.4mm Quad Flat No-leads package requires good eyes. I did the soldering wrong at first, and probably toasted the chip when testing it - at least it did not work after resoldering it under a microscope. I *knew* that I had two extra chips somewhere - but could not find them.

Thus I decided to go with a ready-made breakout board instead. Etched a new circuit board - and discovered that placing the electrodes behind a 6mm fibre cement board did not work even though I had tested it before doing the first printed circuit board.

New strategy: Create 12 "buttons" from a aluminum rod on a lathe. Use a long time figuring out how to solder leads to the aluminum. Drill holes in fiber board and mount buttons. Decide it looks ugly and scratch the concept.

Finally I gave up and bought a water proof stainless steel matrix keypad from It cost me 30 USD for the keypad, 30 USD shipping, and ~15USD in VAT, a total of 75 USD. It is more than I like, but it works! ;-) So now I am back to using a PCF8574 8-bit I/O expander for the keypad.
I have spent so little time on the project lately, that it is hard to remember how far I have come. So tonight I will start a To-do list. Hopefully that will make it a little easier to spend an hour or two on actually working - and not just remembering how far I got the last time.