Four-Leg Two-Motor Reversible Walking Robot
   ===========================================
   a design by Terry Newton

   This circuit incorporates a version of the "Nervous Network", invented
   and internationally patented by Mark Tilden. Commercial usage without
   prior arrangement with the patent holder is prohibited.


                                       .------> enable 
                              __   __  |             
      .----------------------|1 `-'  |-|--------------------*---< + 
      |                      |       | |                    |
      |                     -|       |-|--------*--- 10M ---'
      |                      |       | | 1N914  |       .22u
      *-- 2.2M ------------*-|       |-*--|>|-. `----||-----.
      |             .1u    | |  '14  |        |             |
      |          .--||---*-|-|       |-*------*----- 2.2M --*
      |          |       | | |       | |     .1u            |
      *-- 2.2M --*-------|-|-|       |-|---*-||--.          |
      |             .1u  | | |       | |   |     |          |
      |          .--||-*-|-|-|       |-|---|-----*-- 2.2M --*
      |          |     | | | |       | |   |               _|_
      *----------|-----|-|-|-|_______|-|-*-|-||--.            
     _|_         |     | | |           | | | .1u |    2.2M resistors
                 `-----|-|-|-----------' | |     |    set walking speed
                       | | `-------------|-|-----'    
                       | |               | |          
                       | `----> 3        | `----> 1   
                       `------> 4        `------> 2   

                  __   __
   4'<-----*-----|1 `-'  |-------------*---< +
           |     |       |             |
   2'<-----|--*--|       |-------< 2   |
           |  |  |       |             |
           |  `--|       |-            |                     forward
           |     |       |    2N3906   |                     feeler
   4 >-----|-----|       |-   pnp      |
           |     | 4053  |      .------*-------- 1M ------.   .---
           `-----|       |-     |e                        |   |   \
                 |       |       >|b-- 1M ------*-- 100 --*-->|n.o.\
             .---|       |---.  |c              |             |     \
             |   |       |   |  |         4.7u  |            _|_
             *---|       |---*--*-- 1M --*--||--'  <--.
             |   |       |   |           |    +  increase C
             *---|_______|---'           |       for longer
            _|_                         _|_      backup time
               

    + <------*---------------*-----------------*------< +
             |    __   __    |     +  2.2u     |         3.6 volt 
             `---|1 `-'  |---*------||----.    |         battery
                 |       |               _|_   |  .---< - 
        1 >---*--|       |----< enable         |  |
              |  |       |                     |  |
              `--|       |--*-----> +          |  |           
                 |       |  |                  `--|-- 330 --o +
        3 >---*--| 74HC  |--'   Rear motor        |           
              |  | '245  |                        *-- 330 --o -
              `--|       |--*-----> -             |           
                 |       |  |                     |      charger
        2'>---*--|       |--'                     O
              |  |       |                          /
              `--|       |--*-----> +              /
                 |       |  |                     O  power
        4'>---*--|       |--'   Front motor       |  switch
              |  |       |                       _|_
              `--|       |--*-----> -
                 |       |  |          Stack multiple '245s for more
             .---|_______|--'          current (used 3 in prototype)
            _|_   

   Notes...
                             ----> = output, connect to matching in
     _|_  = ground            
                             ----< = input, connect to matching out
      |                            |
    --*-- = connected wires      --|-- = just passing over
      |                            |

    -- 330 -- = a resistor      ----||--- = a capacitor

    chip numbers used in the prototype: 74HCT14, 74HCT245, TCG4053B 
    (the shack and my old leftover chip stash)
    diodes/transistors g.p. not critical
    core resistors, caps should be <5% tolerence but if it wants
     to turn use high value resistors (22megs, 2 in series for 
     44meg etc) across the 2.2 meg core resistors to balance. 


                    ___                     _
                   |___|  electronics      | |
                   |___|  ___        ___   | |
          rear     |   | |   |      |   |  | |
       gearmotor   ===============================
             _____        |           _.
            |     | ______|_______ .-'  \ front
            |  -------.--------.-------  \ gearmotor
            |_____||  :        :  | \    _\-----.
            |     ||  :battery :  |  \_-'  \     |
            |_____||  :        :  |   \     \_   | reverse
            :  |  :|  :        :  |    \ _.-' :-o| switch
            : -*- :|__:________:__|     :  \ _:. |        /
            `----\'   `--------'        : _-* : \`-------'
            |     |        legstop----> `|----'  \
            |     |                      |       /
            |     |      wire leg ----> /     
            |     |                    /