Parallax PIR sensor (#555-28027)

rickman

I am brand new to this, so please be patient. The PIR sensor (#555-28027) output pin puts out about 3.2 volts when it senses motion. I want to produce a switch closure from this pin. What kind of relay or component will activate a switch closure from this output? Thank you very much.

ElectricAye

rickman wrote: »

...What kind of relay or component will activate a switch closure from this output?...

Hey, welcome to the forum!

There are a number of ways to use the output of the PIR to control other devices. But what we need to know is what kind of device? How much current and voltage does it draw, etc. The more details you can provide, the better.

rickman

Thank you for responding Electric Aye!

I am trying to activate a power door lock actuator based on the output from the PIR.
Here is a link for the actuator: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=330-010
The actuator operates on 12 volts DC, I don't know how many amps it takes.

I tried to use a Solid State Crydom relay that has 3.5-32 volts input = a switch closure output.
Here is a link for the Crydom relay: http://www.alliedelec.com/search/productdetail.aspx?SKU=6820067#tab=Specs
I connect the actuator to a 12 volt supply and connect it 'in-line' on the positive side. When the input side goes high, the output side of the relay completes a line switch closure and powers 12 volts to the actuator. However, the 3.2 volt output from the PIR is not enough to trigger the Crydom relay.

Any suggestions? Thank you very much.

ElectricAye

rickman wrote: »

... However, the 3.2 volt output from the PIR is not enough to trigger the Crydom relay.

Any suggestions? ....

Well, first I guess you already know that this actuator is a "push/pull" whose motion is reversed by reversing polarity. So I'm assuming that what you want, once the PIR activates, is to trigger your actuator for a one-way trip, a one-shot operation. If you don't have some sort of polarity-reversing circuit, then there will be no way to run the actuator in reverse.

So, presuming that you really want to run your actuator only in one direction and not also to reverse it, let me say this: I'm not very good at designing transistor circuits, but if I were in this predicament, I guess I would use the output of the PIR to trigger a MOSFET, maybe something like an IRF3708. I'm just guessing that mosfet will probably be able to handle the currents for your actuator, but that's just a guess since you don't know what sort of currents the actuator draws. In other words, I think the IRF3708 should be able to replace your relay. You might need to add a capacitor across the input of the mosfet, though, so it will stay triggered once it "sees" a voltage from the PIR. I don't know how long the output signal of the PIR stays "on" and it's quite possible that, without some sort of capacitor in there, the mosfet won't stay on long enough for the motorized actuator to complete its movement.

However, if you need to reverse the actuator, you'll have to get more fancy than this. You will need some way to reverse the polarity.

You can find information on the IRF3708 here.

rickman

Thanks for your response Electric Aye!

Yes, I realize the actuator is a one shot deal. I am using it to trigger a door closing on a trap, so that is all I need.

I looked at the specs on the IRF3708 and realize I am out of my league. Here is what I am thinking. There are 3 three connections on the IRF3708. One connection goes to the signal (zero or 3.2 volts) from the PIR sensor, one connection goes to ground and the other one is the switch closure when the PIR sensor goes high? What do you think?

I appreciate your time/input. Thank you very much.

ElectricAye

rickman wrote: »

... One connection goes to the signal (zero or 3.2 volts) from the PIR sensor, one connection goes to ground and the other one is the switch closure when the PIR sensor goes high? What do you think?....

rickman,

I think you're on the right track.
The gif I've attached is from Phil Pilgrim.
Where the image says "Prop" should be the output of your PIR.
The resistor shown above the mosfet represents the in-built resistance of your actuator. The 15 volt supply is replaced by whatever power supply you're using.
As I stated earlier, you might need a capacitor to go from the output of the PIR to ground so it keeps the mosfet gate open long enough for your actuator to fully close. That's something you'll probably just need to experiment with - see if it works without any capacitors and then take it from there. As for the other resistors - The "vertical" resistor is probably not needed since this will be a one-shot deal and therefore you won't need a "bleeder" resistor. The "horizontal" resistor could be maybe 1000 ohms or so, since it acts as a current limiter.

One little warning about the IRF3708: the tab on it, where it screws to a heat sink, is electrically HOT. So you can't heat sink it to ground! (Many components have this tab electrically hooked to ground, but this one doesn't.)

Have you tested the actuator with your power supply yet? Any way to test the actuator's electrical resistance? That might help you figure out how much current that actuator will draw.

I presume you will want to test this actuator, so keep in mind you will need some way to move it back and forth as you work on it. Of course, you can easily open and close it by manually switching wires.

Hope that helps.

kwinn

rickman, if you only need to have the lock go in one direction automatically, and open it manually you could use a mechanical or solid state relay with a double pole double throw switch to do that. Another choice would be an "H bridge" motor driver if you need to go in both directions automatically.