i can vary the voltage by using swithing diodes in a chain to get the right voltage i need so really the voltage that the chip turns on and off at would be best around 2.0 volts.the green laser that i have turns on at 1.0 volts and stays on till the volts drops below 1.0 volts. this works great and i have no problems with this laser. it has its own power supply and the sound card dac voltage goes to a positive and a ground to the four wire setup. it is called a ttl laser driver i guess. the blue laser that i need the circuit for is analouge and so i need to turn the laser on at all times and have a circuit that will open and close the circuit to the laser. if i could get the trigger point to be 1.0 vdc that would be cool or even 2.0 vdc all the way up to 3.0 vdc. over the threshhold voltage should be "on" and under should be "off". i have a mechanical relay and its kinda the thing i need but it is way to slo for the job and the laser turns off and on in the wrong places for where it needs to.
i also have a basic stamp2 board of education and i think it would work to switch the laser but i dont know how to wire it to read the signal from the dac.
thanxs for helping, i sure can use it