I've never used a danger room, but I routinely use impulse ramp driven mine cart repeaters to trigger menacing spike trap arrays, and what you want is just a single trap. I found the design by going to a thread referenced by the wiki on mine cart repeaters.
The design uses a 3 z levels by 7 by 8 footprint.
z
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwwhdhw
wwwwwwwwww
z-1
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwwwwww
wwwwwhwwHw
wwwwwwwwdw
z-2
wwwwwwwwww
wddddddddw
wdwwwwwwdw
wdwwwwwwdw
wdwwwwwwdw
wdwwwwwwdw
wdwwwwwwdw
wddddwwwww
wwwwwwwwww
where
w = unchanged wall
d = dig prio 4
h = channel prio 4
H = channel prio 5
- Carve a track at all the 'd' tiles in the obvious direction.
- Carve N/E impulse ramps at the three ramps (2 on z - 2, one on z - 1)
- Place a hatch cover over the E chute on z and define a track stop there (with a mine cart, of course), and remove the default movement orders for the stop. Hook the hatch to a start/stop lever.
- Build a mine cart activated pressure plate anywhere on the flat track (i.e. not any ramp). I place mine 2 tile N of the drop chute starting the repeater.
- Hook the pressure plate up to the menacing spike trap(s) you want to control.
- Clear out or forbid all the debris in the tunnel, or you run the risk of creating road kill as someone goes to pick it up.
I think you can figure out yourself when to pull the activation lever...