Thursday, March 15, 2012


Well, I shot past my self-regulated milestone of having a working prototype by the end of February.  Not surprising really, especially if you know me.  Time management is certainly not my strong suit. However, as with any good milestone passer, I have lots of good excuses.  A poker tournament and weekend company took up one full weekend, a friends bachelor party in New Orleans took up another full weekend (more when you factor in the recovery period... on both accounts).  Picking out hardware and electronic components was certainly a time-suck (who knew there were 40 different kinds of 6 amp tubular fuses?).  And most recently, I realized I had to change resistor values on several parts of the circuit, which would normally not be a problem, but I do not have much of an assortment of the surface mount parts, so I had to order some more and wait for shipment.

However, since I've last updated you, I have built the power circuit board**, created all the cable assemblies to connect the internal components together (buttons, LCD screen, temperature module, power, etc).  The cables took a little longer than I had expected; they weren't especially difficult, just time consuming.  I also performed all the power and continuity checks and then programmed the on-board PIC. 

Then.  Finally.  Last night.  It was time for me to breath life into my creation!

 It still has a few bugs related to the circuit that I need to patch up, but for the most part... IT WORKS!  It was a momentous occasion!

You will, however, notice from the picture below, that it needs to learn a little discretion and put another layer on, but we'll get to that (he's going to so embarrassed when he grows up and realizes I posted naked pictures of him all over the internet.)

Anyway, that's all for now.  I've got a case for it and once I get some bugs worked out, my next task is to get it all put together in the case.

****Especially Geeky Power Circuit Explanation****
My power circuit consists of a terminal strip that connects the input and output power cords to the circuit board.  The circuit board then transforms 120V AC power to 6.3VAC power through a transformer.  The 6.3VAC coming out of the transistor is converted to 5VDC through a series of components.  First a rectifier converts all the negative portions of the AC sine wave to positive.  When graphed, this creates a series of humps instead of a sine wave.  A capacitor, which temporarily holds a charge (similar to a very short term battery), evens out the signal to a noisy (wavy) DC voltage.  Then a voltage regulator IC takes the noisy DC signal and converts it to a clean 5VDC signal.  The picture below shows a graphic representation of what each stage looks like.