Ideas needed

[Optical]

*please move if this is the wrong forum*

Hi, here is my problem for you:

I have a varying voltage spike from a piezo (0~20V) and wish to trigger (or mimic) 2 switches with it, the first switch is to close when the input spike is detected, and the second switch is to close after the first at a time proportional to to the amplitude of the voltage spike..

i have an idea so far, but am unsure if its the best idea as i am trying to keep components at a minimum as i am going to need ~15 of these circuits..
the power available is 0 - 5V

i will post up the schematic soon but this is how it works so far:
I have the piezo voltage spike put through a half wave rectifier then into a sample and hold circuit, which then is fed into a ramp generator, (basically a constant current source controlled by the voltage input charging a cap) this ramp is then fed into 2 comparators one triggering at 200mV then the other at 4.8V thus providing the switches at a different spacing depending on the input voltage..
Ive had to use rail to rail opamps (currently trying out the LMV324's)

I am open to all ideas!
Thanks
Matt

oh, to see why i want to do this you can check here: http://www.diyaudio.com/forums/showt...727#post250727