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Reply to "Semaphore and 555 Timer Circuit"

The jumper instructions look correct.  To be clear, we're talking about a DIY hack to use the same PCB board for either the CC or CA.  No doubt one year from now we'll look back and wonder what were we thinking (or smoking)!  

Anyway, to perpetuate the hack, I suggest you place ALL instructions for the conversion in a neat table on the 1-sheet schematic.  The table would itemize the differences between CA and CC.  That is, identify the 3-pin jumper settings, the change in the 6 base resistors, and the orientation of the NPN transistors.  As I think about it, since you must "commit" to CC or CA by soldering different components anyway, there's no added value to having the 3-pin jumpers with those push-on programming connectors.  In other words you need the pads and solder a jumper wire from 1-2 or 2-3 accordingly.  Or, if we're in learning about DIY PCB mode, another technique actually used more than you'd think is to make the 3 pads close enough to make it easy to place a blob of solder to bridge 1-2 or 2-3.

Again, if messing around with PCB design, a very common practice for multi-use boards is to use the white silkscreen to identify which board type you assembled.  So you'd print a white circle or square labeled CA and another marked CC.  When you assemble the board, mark it accordingly.

 

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