Several weeks ago, I started designing a generic User Interface (UI) for my Propeller Microprocessor Projects (see previous post). The UI was planned to be an adaption of circuits that I am already using with current project (see previous post). The new adaptions included I2C Converters and stand-alone on-board 3.3V Regulator.
The UI board layout was sent for Manufacture on May 14 and was just received a few days ago. I was anxious to load a board with parts. My initial strategy was to load a board with as few parts as necessary to do some initial tests. But once I started loading, I decided to load all of the parts, starting with simple resistors and capacitors (what could go wrong? :-). Prior to installing the Major Expensive Components, I checked the LED circuits and did some simple resistant test - ALL looked good.
Then, In steps Murphy and Assumptions:
When I went to my parts storage bins for the 3.3V regulator, I could not find a SOT-89 3.3V regulator (similar to my often used L78L05 5V SOT-89 regulator). Maybe I have never had one, or maybe they do not exists with the foot print I used in the layout. But my board, as designed, defiantly needs one. When I laid out the board, I assumed they were in the bin. Now I will need to check availability and order something that will work.
When I went to my parts storage bins for the MCP23017 Dual I2C I/O Expander (16 pins of GPIO), I could not find them. I know they exist, and I thought I had order several, but I could not find them. My board as designed needs two. For this design and layout, I decided to use the Dual I2C I/O Expanders (similar to the previous used single expanders). They require less space for the available output pins, and they require one less device address on the I2C bus. So, now I need to order even more parts, to finish the build.
|UI With Traditional LCD Display|
( Blue, Purple and Green Boards, who's idea was that? Murphy!! )
|UI With Alternate Display|
I found the SOT-89 3.3Volt Regulators at Mouser, and they will be on order soon, along with a few other parts.