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  1.               Automatic computer powerdown on hang circuit
  2.                         by WA8BXN 
  3.  
  4.         This circuit connects to one or more serial ports from the computer
  5. to the tncs and will drop power on the computer if there is no data from
  6. the computer in some given period of time. Normally the ID sent periodically
  7. will generate data out from the computer, resetting the time out interval.
  8.  
  9.  
  10.  
  11.                                 +12 V
  12.                                  |
  13.                                  |   
  14.                   +--------------+--+------+
  15.                   |                 |      |
  16.                   |           Pin 8 |      | Pin 4
  17.                   |             +----------------+
  18.                   /             |                |       1N914
  19.             R1    \             |                |
  20.            2 Meg  /             |                |  Pin 3   |
  21.                   \             |                |--------|>|--+-----+
  22.                   |             |                |          |  |     |
  23.                   |      Pin 7  |                |             |     |
  24.                   +------------ |                |            ---    $ Relay
  25. RS-232 Pin 2      |             |                |      1N914  ^     $ coil
  26.  |                |             |                |            /-\    $
  27.  |                /             |    555         |             |     |
  28.  -                \   R2        |                |             |     |
  29.  V  1N914         /  100K       |                |             +-----+
  30. ---               \             |                |             |
  31.  |                |             |                |             |  Use contacts
  32.  |     2N2222     |      Pin 6  |                |             |  to drive 
  33.  |          /-----+----+--------|                |             /  larger relay
  34.  |        |/      |    |        |                |        180  \  to control 
  35.  +---/\/\-| (npn) |    +--------|                |       ohms  /  computer AC
  36.      10K  |\      | +    Pin 2  |                |             \
  37.             v   -----           +----------------+             |
  38.             |   ----- 270 microF   Pin 1 |                     |
  39.             |     | -                    +---------------------+
  40.             |     |                      |  
  41. RS-232      |     |                      |
  42. Pin 7 ------+-----+----------+-----------+
  43.                              |
  44.                             ---    (ground)
  45.                              -
  46.                              .
  47.  
  48. R1+R2 along with capacitor determine ON time (larger resistance gives more
  49. time).  R2 determines OFF time. On time should be somewhat longer than the
  50. ID interval. 
  51.  
  52. Relay is radio shack 5 VDC reed relay, 250 ohm coil, 20 mA. Contacts only 
  53. good for 1 AMP so use them to drive larger relay that can handle computer
  54. AC line current. Circuit starts at ON when power is applied. 
  55.  
  56. If more than one port will be connected to the input, use separate diodes
  57. for each port into the 10K resistor. 
  58.