556

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Dual 555 universal timers.

When 1CV or 2CV are not connected they are held at 2/3.VCC through a 5k/10k divider.

      +---+--+---+           +------+--------+------*---+-----+
 1Dis |1  +--+ 14| VCC       | /RST |  /TR   | Thr  | Q | Dis |
 1Thr |2       13| 2Dis      +======+========+======*===+=====+
  1CV |3       12| 2Thr      |  0   |   X    |  X   | 0 |  0  |
/1RST |4  556  11| 2CV       |  1   | < CV/2 |  X   | 1 |  Z  |
   1Q |5       10| /2RST     |  1   | > CV/2 | < CV | - |  -  |
 /1TR |6        9| 2Q        |  1   | > CV/2 | > CV | 0 |  0  |
  GND |7        8| /2TR      +------+--------+------*---+-----+
      +----------+