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From: robin@uhunix1.uhcc.Hawaii.Edu (Robin Amano)
Newsgroups: sci.electronics
Subject: Re: TTL Logic Probe
Message-ID: <10202@uhccux.uhcc.Hawaii.Edu>
Date: 7 Nov 90 21:17:26 GMT
References: <16525@hydra.gatech.EDU>
Sender: news@uhccux.uhcc.Hawaii.Edu
Organization: University of Hawaii
Lines: 88

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?

This is a simple one:

+5V DC  O---------->|----------/\/\/\/----------|
                  L1             R2             |
     					        |
                               _________________|
PROBE   O------\/\/\/\_______|/        _________|
                  R1         |\,_____|/
                                     |\,________
                             Q1                 |
                                     Q2         |
GROUND  O---------------------------------------|
                   

   SYMBOL       QTY            DESCRIPTION       

   Q1,Q2         2             npn silicon transistor
    R1           1             27K ohm, 1/2 W resistor
    R2           1             150 ohm, 1.2 W resistor
    L1           1             LED

the commas on the transistors are where the arrows should be, remember npn.
this is a simple led on = 1, led off = 0

here's another one:
     
       +5 V
         O
         |
         |
         |
         /
         \
         /   150 K
         \   1/8 W
         /   5 %
         \                            
         |                            |\	
         |                            |  \
         |                     |------|    O------|
         |                     |      |  /        | 
         |                     |      |/          | output
input >--|---------------------|                  |-------|
         |                     |      |\          |  led  |
         |                     |      |  \        |       |    led glows if
         \                     |------|    O------|      \ /   input is logic
         /   100 K                    |  /               ---       low 
         \   1/8 W                    |/                  |
         /   5 %                                          |
         \                                                |
         |                                              -----
         |                            |\                 ---
         |                            |  \                -
         |                    |-------|    O------|
         |          |\        |       |  /        |
         |          |  \      |       |/          | output 
         |----------|    O----|                   |------|
         |          |  /      |       |\          |  led |
         |          |/        |       |  \        |      |     led glows if
         |                    |-------|    O------|     \ /    input is logic
         |                            |  /              ---        high 
         /                            |/                 |
         \   100 K                                       | 
         /   1/8 W                                       |
         \   5 %                                       ----- 
         /                                              ---
         |                inverters are CD 4009          -    neither led glows 
         |                     leds are MV 5020                  open circuit
         |
         |
         |
       -----
        ---
         -   

hope this helps!!

--
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Robin Amano            |  Internet: robin@uhunix.uhcc.hawaii.edu
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