Brake Cooling Circuits

[Terry Sare]

Look on Nationals Web site http://www.national.com/pf/LM/LM555.html  for the 555
or other one shots. Fred's comment about attaching the brake switch is good,
except that I would use a 555 in a one shot setup. That way you can adjust your
on time a little more accurately and a 555 can drive a pump or whatever easier.
Lousy ASCII Art Follows:

        +12V          +12V               Ground 1                        | +12V
     |          |               Vcc     8 +12V                      Pump
     |          Resister  Ra          Reset   4  +12V            ___________|

     R 10k          |                              |/
     R          |               Output  3 --------RRR-------|     2n2222
     |------------------------------- 2 Trigger                         |\______
Brake Switch          |------- 7 discharge  555                           |
     |          |------- 6 Threshold          5  -----               Ground
     ground          |                         |
               Cap C                         C (0.01uF)
               |                         |
               ground                         ground

See LM555C datasheet for Ra and C and the real schematic -- Add a cap to ground
on the trigger if to much noise. Add a 12 V zener across the pump so you don't
blow the 2n2222. Lottsa bypass caps.


Terry
<snip>
The previous suggestion of a 555 timer (or the 7555, or any of the
derivitives) could work.  Even easier, a simple R/C network that shorts
with a resistor when you hit the brake, and re-charges through another
resistor when you release.  The cap won't discharge all the way for short
braking spells, and if it does, you time the R/C network to give you 5-6
seconds max.
<snip>