PIR and electric lantern

PIR and Lantern

I wanted to be able to have an electric lantern turn on as I entered the room. I decided to use a PIR sensor (Pyroelectric (“passive”) InfraRed sensor) as the detector. First I had to use a breadboard and the parts to get it worked out.
IMG_6057 (1)
There is a second transistor on the breadboard as well as an LED and resistor. I didn’t use these in the project. They were left over from an Arduino project.

I am powering the PIR with 5v from a USB phone charger.  The three AAA batteries inside the lantern will light up the lantern’s LEDs.

A PIR has three pins.  DC+ in, Output, and Ground (-).  I connected the Output pin to the Base of the transistor.  At first I used a 2n3904 transistor.  This worked will when I as just using an LED on the breadboard as the light.  When I hooked up the lantern there was too much power and it bled through.

I put a guitar pick between one of the batteries on the positive side and put wires from the battery and the post where it was to touch.  It was like adding a switch.  The 2n3904 didn’t stop the electricity from flowing.  I had a 2n2222 on hand and ready that it can handle about three times as much and the 2n3904.

The schematic ends up looking something like this picture.PIR project schematic

Perhaps I should be using a resistor between the PIR and the Base of the transistor.  So far the transistor doesn’t seem to get hot or mind.

Once I had the design working I had to solder everything together. I could not find an electronics board with all the holes pre-drilled. I knew I have one somewhere. I decided to use an old iTunes gift card as the circuit board. I drilled holes in it for the PIR’s pins, as well as for the transistor. I used short jumper wires to create the wiring I wanted. To connect the DC + and – pins of the PIR I soldered short wires to them and poked the other ends up through holes drilled in the card. I used a USB cable taken from a broken mouse and plugged it in onto the exposed pins I just created. For the fires running to the lantern I soldered two wires to the collector and emitter of the transistor and poked the other ends up through the card. I then soldered longer wires to those newly created pins.

Gift card circuit board topGift card circuit board bottom

Now came the tricky part. I took a small piece of an expired credit card and glued aluminum foil on both sides. After the super glue was dry I checked to see that the foil was not touching from one side to the other. I soldered the two long wires to the aluminum, one per side. Now I had a separator that I would be able to use inside the battery case of the lantern. I removed one of the batteries from the lantern and put this little piece at the positive end of the battery while I reinserted the battery. I think using a copper clad circuit board would have been easier to work with. You know the kind I mean, copper on both sides so you can etch your own designs with some acid. I think the closest store that might have this in stock, on short notice, is about 45 miles away.

I read information about the PIR from Adafruit. (www.adafruit.com) I love the NeoPixel LEDs they sell.  They are easily programmed and are very bright.

PIR Lantern animated gif

One thought on “PIR and electric lantern”

  1. After learning more about transistors, I now know that I need to include some resistors in this circuit. I’m going to have to do some calculations and add them in. – Greg

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