12VDC PIR Sensor and lighting circuit

Thread Starter

Eric Moseley

Joined Dec 6, 2017
3
Hello everyone,
I'm fairly new to all this so please excuse my ignorance.

I am trying to power a PIR sensor with a deep cycle 12vdc battery and get everything to light up a 12Vdc bulb. Basically an outdoor timed motion sensor light. Now I have an idea how to hook this all up, however I'm a little fuzzy on how to work the PIR sensors 3.3V output to power the 12Vdc bulbs. Would a relay work, because I have a relay laying around? Do I need to use transistors/resistors? Is there a better way I don't know of, ha. Thanks for any assistance!

PIR sensor: https://www.amazon.com/gp/product/B012ZZ4LPM/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1
Bulb: https://www.amazon.com/gp/product/B01MY6U83G/ref=oh_aui_detailpage_o07_s03?ie=UTF8&psc=1
Relay: https://www.amazon.com/gp/product/B00VNDFEIG/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
 

Thread Starter

Eric Moseley

Joined Dec 6, 2017
3
Thanks for the help, one more thing if you don't mind.
I will set it up like the image below, at least it looks like it will work to me. However I do wonder if I could remove the relay/diode all together and just use the PIR's output to drive the light. Thanks again.
 

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JohnInTX

Joined Jun 26, 2012
4,206
Thanks for the help, one more thing if you don't mind.
I will set it up like the image below, at least it looks like it will work to me. However I do wonder if I could remove the relay/diode all together and just use the PIR's output to drive the light. Thanks again.
No, you'll need the sort of driver transistor shown by @Dodgydave and in your sketch. The reason is on pp3 of the datasheet. It shows the output swing as 3.3V max. Besides the lower voltage, it is a logic level output and doesn't have the current capacity to drive a relay. Sorry.

You could just use a bigger transistor that would drive the LED bulb directly and skip the relay.
 

Thread Starter

Eric Moseley

Joined Dec 6, 2017
3
So if I were to use a 2n2222 (which is ~70V @ ~600MA) transistor with a 1K ohm resistor that could power the bulb directly?

Apologies for pestering, but using a transistor alone to power the circuit would be fantastic and is blowing my mind.
 

ElectricSpidey

Joined Dec 2, 2017
1,193
No, you will need something bigger, something that can handle 1.5 amps, and at least 1 watt. A TO220 package most likely.

Get a small TO220 heat sink just to be safe.

And you might need a different base resistor depending on the transistor, you want to make sure you drive it into saturation.
 

ElectricSpidey

Joined Dec 2, 2017
1,193
On second thought, I would probably use a MOSFET in this circuit.

Advantages…

No need to heat sink at that current.
Much less v-drop
No load on the PIR.

I think what you would need is called a low level MOSFET but I can’t say for sure, but I’m sure somebody else can steer you in the right direction.
 
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