Hi all,
I am a newbie to electronics and have been having fun with LED's. I bought a PIR motion sensor to play with. After I got it, I noticed that the output current is 10ma with a max Vin of <6v. I put it on a breadboard and using a white LED with 4.5v to the "in" of the PIR , it puts out a little light so when I walk in the bedroom, I can get in bed without turning on the overhead or waking my wife. But now I want an output of 25ma so the light is brighter by a bit. I read the transistor section but am still confused. Can anyone draw me a quick circuit that I can add to this to make the LED brighter? I am using a three battery battery pack with alkaline batteries.

Thanks for reading,
Robert

 

don't forget the current-limiting resistor for your LED. Have you tried one of the super-bright LEDs?

 

Radiohead,
All I can get out of the PIR sensor is 10ma so a hi output LED won't work. I want to add a circuit to the Vout of the PIR sensor to boost the 10ma to 20-25ma to brighten the 5mm white LED. Maybe a joule thief?

Robert

 

well..its a simple task..but it depends on whether u know how a BJT works. Its a transistor and it takes a current input at the base and multiplies it with a DC gain to give a certain current at the collector. Of course, i just gave u a very coarse overview of it and to implement it u would need a working knowledge of a bjt.

To answer ur question, attach the base of the bjt to the output of ur ciruit via a 1K resistor and connect the emitter terminal to the ground. Connect the collector to the VCC( the +V of the power supply) and add a current limiting resistor to the in series with a LED which is connected to the collector.

Ive attached a diagram below. See if this helps.

 

It looks to me that the input from the PIR isn't enough to bias the transistor (turn it completely on). How much voltage are you using?

 

By the way, are you using the Parallax PIR module # 555-28027?

 

If so, it outputs single bit TTL/CMOS compatible logic. Instead of using this to try to bias on a transistor, use the pulse to trigger a 555 (in a one-shot config) and turn on an LED. See the 555 tutorial in the blog section of this site.

 

hmmm the 555 timer in monostable mode seems like a good idea but it'll consume far too much power just to remain in the operating mode. I think if claychps figures out what voltage is he getting out of the PIR then he can easily use either of the implementaion..keeping in mind that he only needs to brightly light the led.

BTW..since your a senior member..im guessing you might have some prior knowledge of 555 timer chips..can u take a look at this thread :
http://forum.allaboutcircuits.com/showthread.php?t=44721

 

Thanks for the replies. Radiohead, I am using the PIR from Adafruit and it uses the BISS001 PIR IC. From the specs, max current output is 10ma and Adafruit suggests no more than 6vin. I am using 4.5v from three alkaline batteries, barely enough to light the white LED with 2.6VF. I'll try the transistor circuit that Chimera suggests and up the Vin to 5v. That should help even tho the better half likes it just as it is...lol. Again, thanks guys for taking the time to help a real Newb.

Robert

 

Let me breadboard something. I'll get back to you.