PIR sensor help
aEx155
Posts: 2
A search on the PIR sensor didn't turn up much so I'll see if a new topic can help.
I bought a PIR sensor from Radioshack in hopes of using it to control an IKEA LED lamp. The output of the sensor is fed to the gate/base of a MOSFET/transistor, which is supposed to switch the light on and off.
With the MOSFETs I have (RFP50N06) and the transistors I have (a MJE3005T and a TIP120), I haven't been able to get anything to pass the current it should, and when I use the transistors, it does this weird flashing routine even if nothing in the room is moving or changing.
Any ideas on how to increase the current though the MOSFET/transistor?
I bought a PIR sensor from Radioshack in hopes of using it to control an IKEA LED lamp. The output of the sensor is fed to the gate/base of a MOSFET/transistor, which is supposed to switch the light on and off.
With the MOSFETs I have (RFP50N06) and the transistors I have (a MJE3005T and a TIP120), I haven't been able to get anything to pass the current it should, and when I use the transistors, it does this weird flashing routine even if nothing in the room is moving or changing.
Any ideas on how to increase the current though the MOSFET/transistor?
Comments
Go to "google" and do a search on "pir site:forums.parallax.com"
or click the link below:
"www.google.com/search?num=100&hl=en&lr=&client=firefox-a&hs=WC6&rls=org.mozilla%3Aen-US%3Aofficial&q=pir+site%3Aforums.parallax.com&btnG=Search&aq=f&aqi=&aql=&oq=&gs_rfai=
You should get almost 200 hits.
I hope this helps.
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- Stephen
Any chance your PIR is responding to the flash of the LEDs and causing a feedback problem? Can you cover the PIR to test that?
You should probably provide some details: what the output of the RadioShack PIR is supposed to be, for example. How many volts, current, etc the LED lamps needs. I suppose it's possible you're not outputting enough voltage to drive the MOSFET, for example. But that's the kind of thing we need details to determine. Also, the output of the PIR might be just a single pulse instead of a prolonged signal, so we need to know things like that.
Here's a link to his data sheet for anyone interested:
www.fairchildsemi.com/ds/RF/RFP50N06.pdf
As far as I can tell the sensor from RS is exactly the same as the one Parallax sells (http://www.parallax.com/rs). All the information I have comes from its datasheet online (http://www.parallax.com/Portals/0/Downloads/docs/prod/audiovis/555-28027-PIRsensor-v1.4.pdf).
As far as powering the LED, with my 5V supply I'm using a 1.8 ohm resistor and it gets ~500 mA. You might be right in saying the transistor/MOSFET isn't getting enough current, but I don't know how I can increase that.
I tried replacing the MOSFET with a transistor + relay. It works (turns on the light) but it does the weird flashing thing. This leads me to think that there may be power spikes that reset something in the sensor; does this make any sense?
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- Stephen
Actually, what I said was that you need to be sure your MOSFET gate is getting enough voltage, not current. It looks like 4 volts should be able to drive the MOSFET for your application, I think. If for some reason the MOSFET gate is not getting enough voltage, then it might work under low loads (for example, a single LED) but then act weird when you place higher loads on the circuit (your lamp).
Another thing you might try: maybe place some capacitors across the power supply of the PIR to help stabilize its power, to smooth out any glitches that might be happening there. I think the PIR is somewhat sensitive to power instabilities.
hope that helps,
Mark