🚀 go-pugleaf

In article <16525@hydra.gatech.EDU> jgb@prism.gatech.EDU (James G. Baker) writes:
>   Anyone out there have schematics or suggestions for building a TTL (only)
>   logic probe.  I took one of the little hand-held probes apart and found
>   a terrifying amount of capacitors, resistors and unknown DIP chips.  Can
>   I make one simply by using a few latches, etc?

You want quick and dirty?  Here's what I built:


             +----|>|----+ <-- tri-color LED (red/green)
      |\     |           |
   +--| >O---+           +----+
   |  |/     |           |    |
   |         +----|<|----+    |      probe tip (nail)
   |                          |              |
   |                          |              V
   +--------------------------+--/\/\/----||====>

OK, I *said* dirty...  This probe *WILL* load your circuit, it won't catch
glitches (unless you have great eyes :-), and it doesn't have a latch.  But
if your circuits are simple TTL, this works pretty well.  The tri-color LED
lights red for logic 0, green for logic 1, and yellow for high freq signals.
It's small and easy to build (I clipped the leads off the 7400 and soldered
directly to the tabs, stuffed the thing inside an old pen (the extra fat 
kind)).  I'd welcome any ideas for a more complex version of this, especially 
one to isolate the probe tip from the circuit.  I do like the tri-color part.
--
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Mike McManus                        Mike.McManus@FtCollins.NCR.COM, or
NCR Microelectronics                ncr-mpd!mikemc@ncr-sd.sandiego.ncr.com, or
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