How do I make a break beam sensor that triggers a relay?

Question

I want to make a break beam sensor that will trigger a 12v relay. I am trying to add a second stage to a coilgun and I want the second stage coil to fire when the projectile passes through the break beam sensor. I want to power the relay and the sensor with a 9v battery. Also the more simple the circuit the better. Thanks

Answer 1

A relay may not be fast enough.  You need an electronic 'relay', such as an SCR, Triac, or MOSFET switch.

This paper shows the basics of what you need.

http://www.microsemi.com/micnotes/601.pd...

I have built circuits like this before (for other purposes), and that is exactly what I would use for a coil gun if/when I get around to experimenting, myself.

The input pulse can be done using something like this:

http://ourworld.compuserve.com/homepages...

It would be OK to feed the output of the opamp to the trigger transformer, so long as you use an opamp with a short-circuit output rating of 'indefinite'. OR... put a capacitor in series with the output and a resistor in parallel with the trigger transformer.

Pulse Engineering makes a huge line of trigger transformers for this purpose.  Sometimes you can get them on E-bay for cheap -- or from surplus electronics outlets.

Good luck with your project.

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