🚀 go-pugleaf

  that is a circuit i have memorized:
                    
                                           vcc
                                            |
                             +----------+   |      
                      +------+ 1      8 +---+---/\/\/-+       
                      |      |          |   |    r2   |
                      | +----+ 2      7 +---|---------+
           d1    r3   | |    |          |   |         |
         +-|>|--/\/\/-|-|----+ 3      6 +---|-+-/\/\/-+
         |       +----|-+    |          |   | |  r1
         |       |    | | +--+ 4      5 +-x | |
         |     --+--  | | |  +----------+   | |
         |     --+--  | | +-----------------+ |
         |    c1 |    | +---------------------+            
         +-------+----+                                    
                      |                                     
                    -----                                  
                     ---                                   
                      -                                    

  it works by charging c1 to 2/3 vcc through r1+r2, then discharging c1 to 
1/3 vcc through r1 alone.  don't recall the r1/r2/c formulas offhand, but
you should be able to figure them out from the above.
  notice also: the duty cycle is set by the ratio of r1 to r1+r2.  you can't
quite get a 50% duty cycle, although you can get close.  (actually with some
circuit mods one can get any duty cycle desired)