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Need help with building a ir trigger

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mr ed

New Member
I have a project that needs an infrared sensor that turns on a high voltage Mosfet when something is blocking the ir light coming from the ir emmiter. i have searched around, and cannot find any plans for what I need, and am a beginner, so have no idea where to start, I do not have any parts yet, so it is not being built aroung anything.
 

crutschow

Well-Known Member
Most Helpful Member
What speed do you need for this switching function?

What is the distance from the emitter to the detector?

If the speed is relatively slow, you could use an IR phototransistor to directly drive the Mosfet gate. You would connect the phototransistor emitter to ground and a resistor from the collector to say 10V. The gate of the Mosfet is also tied to the phototransistor collector. Thus when the light is interrupted, the phototransistor turns off, the collector voltage goes high and turns on the Mosfet.

The value of the collector resistor somewhat determines the speed and sensitivity of the circuit and it's value can vary from about 1K ohm to 100k ohm or higher. A higher resistance gives more sensitivity but lower speed.
 
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colin mac

New Member
Something like this. Increase the value of Vcc and R to get the output needed to turn on the mosfet as said above. Depends on the distance though. You could a few more IR LEDs to increase the range.
 
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mr ed

New Member
Sorry it took me a while to get back to you, I realize how unclear I was. But what i need is going to be used in building a 4 stage coil gun. the first stage is triggered by a switch, and the others will be triggered by seperate sensors. The sensor is supposed to turn the mosfet on when the projectile is blocking the ir beam, that will let electricity flow to the mosfet to switch the power from the capacitors to the coil, and then turn off the mosfet once the projectile clears the ir beam. I have thought about having the ir receiver directly switch the mosfet, but I think that the ir receiver wil trigger a lower powered mosfet which will trigger the larger mosfet. I am not sure what components I need, I have tried looking at them, but only found mosfets that need 10 VDC to trigger, and ir sensors that are only rated at about 1.7 V, I guess that what I need to know is what parts I need, and which configuration. Also the speed of the ir sensor does not matter, because the distance from the coil can be adjusted, but I need a mosfet because it is on/off and it is high speed, keeping variables low, is always good.
Thanks for your help.
 
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mr ed

New Member
If you could draw up a circuit with values for the components that I will need, or make a little list, by the way I need three seperate trigger circuits. this would help, as this is my first time building a circuit from scratch with little knowledge. I used to build little kit circuits that teach you nothing about electronics, but gets you a cool trinket.
Also could you explain your diagram.
 
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