Saturday, January 23, 2010

Phase 2 is complete

I worked until 5am Friday morning completing the information I need to send in for Phase 2.  I got up after a nap and was preparing to email what I had done the night before.  In my email was a note saying that since they wouldn't start judging until Monday, we could submit our material through Sunday.

While I was pleased that I had another 2 days, I was disappointed they waited until the last moment to let us know.  I could have done with more sleep.

I used the extra time to complete the Chibi RF driver support in my sensor design, and got the code to compile error free.  I grabbed a few more screen shots of the simulation, and added in PDF's of the schematics and board designs.  Then I had to go back and edit the text of my submission to reflect these changes.

Instead of the partially baked submission I was preparing on Friday, I've now got what I feel is a completely baked entry, and its only Saturday evening.

When I started to work on the BOM, I expected to find some part shortages, based on what I'd been hearing on the web.  I only found one out of stock part, out of the 60+ unique parts in my design.

But I did notice some "sub optimal" decisions.  I had used through hole mount LEDs when I could be using SMT.  Another example is that I noticed the temperature sensor I had chosen has a minimum operating voltage of 2.3volts.  Not good when you are running a device on two AAA batteries.  I found a slightly more expensive National part that is good down to half that.

The backlight for the LCD display I am using draws 60mA typical.  The 1/10 watt 0603 SMT resistor I had put on the board layout wouldn't deal with that well.  I need to change the board to use a 1206 1/3 watt.  There are several other changes I've decided to make.  Fortunately, most aren't functional problems, rather they are just better decisions, like SMT instead of THP LEDs.

The net is that every time you look at a design a different way, you find things that need to be changed or improved.  I found changes I needed to make while I was doing place and route.  I found changes  when I sketched out how the boards would be connected with each other and the LCD and radio.  I found changes when I was writing the code.  And I found changes when I was costing the BOM and checking availability.  I'm hoping I don't see too many more changes when I go back to make the updates to the hardware I've already decided to make while working on the software and BOM. 

In a normal work environment, I usually don't write the code, and I don't cost the BOM.  Other specialists do those things.  But then I miss out on those different perspectives and the detailed re-examination of the design those efforts entail. 

Since I had the time, I tried again to find an SPI user component for the VMLAB simulator.  It appears that none exists.  Since there is an I2C simulation component, you would think that SPI would be easy.  I will have to make one myself if I hope to do any  serious simulation work.  Yet another thing I usually get to farm out to a specialist that I will have to do myself.

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