Battery-Operated Motion-Activated LED Lamp

If you'd like to put a light somewhere that doesn't lend itself to being wired in, this may be just what you need.

This is a simple project to build. There are only 3 parts -- a PC board, a lamp, and a battery.

I placed one at the bottom of a dark stairway so I don't have to turn the overhead light on and off. It runs on an ordinary 9-volt (or a 12-volt) battery, so it works anywhere.

A friend put hers in the camper on her pickup truck. Another friend put theirs by the door so the room has some light as soon as they walk in. It doesn't "shut off" during the day, but the whole thing costs less than $3 plus the battery and some cheap or leftover LED's ($1).

My lights are small LED's, but you can customize it to make as much light as you need as long as it works on 9 or 12 volts. You could power higher-voltage devices through the relay, but that's beyond the scope of this Instructable.

My battery lasts for about a year. If you add a lot of LED's, your battery life will be shorter, obviously. The relay is advertised to handle 5 amps (or 60 watts), which is more than large enough for nearly anything you're planning. The relay is marked "20 Amps" but you'd be foolish to expect it to last long at that workload.

Once activated, it stays lit for about 15 seconds after it no longer senses any movement. The sensing distance is about 2 feet away.

I bought everything on eBay, nothing is very expensive.

Search for DC 12V 5A IR Pyroelectric Infrared PIR Motion Sensor Detector -- these cost under $3

Pick out some LED's. I had some left over from another project. Match the voltage to your power supply (9 volts, 12 volts, etc.) Do an eBay search for whatever kind you like. In my case, since I was lighting up a dark area, they don't have to be very powerful. I had a strip with a plug on the end.

You'll want some 9-volt battery snaps. They're 10 for $1 on eBay.

You'll need a rectangular 9-volt battery or similar power source.

I put the board and the battery inside an Altoids tin (with some duct tape on the bottom so the PC board doesn't short out on the metal case).

The LED strip is designed to produce 3 independent colors of light. When all 3 are turned on, it's just white light.

I wired the Negative side of all three LED colors to the Yellow wire (which then connects to Negative wiring when the sensor sees movement). The Positive sides of the LED's go to the Red wires.

I soldered all the wiring (YouTube videos will show you how) but if you're not up for that you could just twist the wires together and add some twist-on wire connectors, or electrical tape, or even scotch tape if you're on a limited budget ;-) or just some glue to insulate everything and hold it together. Nobody's going to get a shock or a fire out of this (unless you try using Lithium batteries or something).

You'll probably want LED's that already have wire or connectors on them if you don't want to solder. The connector on the LED strip I had lends itself to "wire wrap" -- a small specialized tool used with extremely fine wire that wraps around a small post.

Any red wire is Positive +, Black wires are Negative -, the Yellow colored wire is the "switched" wire used to turn something on and off. You'll use the Red wires to power the sensor and lamps, the Black wires to connect all the parts to ground, and the Yellow wire to switch the LED's (the "load") on and off.

You'll use the Yellow wire to do the switching, connect it to the Negative - side of the LED's (actually, you're switching the Ground/Negative side of the load on and off. This is NOT the way high-voltage home AC wiring is used, but for low-voltage it's fine). The Positive + side of the LED's goes to the Red wires.

If you want it to work backward (load is always on, then turns off when movement is detected) just switch the polarities at the Yellow wire. (Yellow wire to Positive LED lead, Black wire to Negative LED lead.) You might even think of a project where something is always on, then turns off when movement is detected. In other words, there is a "Normally Open Switch" state (turned off) and a "Normally Closed Switch" state (turned on) for the switching done by the relay. Those states are reversed when the sensor detects motion, stay reversed for as long as there's motion, then waits another 15 seconds, then goes back to its original state. Technically, you could use this circuit to have something turned on all the time, then detect motion and turn off the item that's turned on, and turn on a second load while the first one is turned off. Moments later, they would go back to their original states.

For that, you might consider adding an AC power supply, since something will always be drawing power.

Remember the sensor will work on 9 or 12 volts, your only limitation is the LED voltage specification. There are tons of 12-volt LED solutions intended for cars. This circuit could also be used wired to a car with proper fusing and care. How about an outside light that turns on when your bumper (sensor) is within 2 feet of anything?

You probably can't blow anything up if you do something wrong. If it doesn't work at first, just take a break and look at it again later. Start out simple and add more LED's later.

If you want to restrict or narrow the sensed area, you can put little pieces of tape over the sensor. For example, we have a motion-activated trash can lid in the kitchen. But it's in a tight area, and we don't want the top to pop open every time someone walks by. A little black tape narrows it's sensed area.

This control can be used for just about any small-ish load. LED's and batteries are DC, but the relay is just an SPDT Switch (single-pole, double-throw) switch, so it works with AC devices, too.

If you want the load to be located some distance from the sensor, you'd be better off extending the powered lines (red and black) rather than the sensor wiring. Extending the wires on the sensor would run the risk of having this sensitive circuit connected to a long "antenna" that could pick up other signals, causing problems with consistent results. The powered wires are less likely to pick up stray signals and respond.

There are more interesting circuit boards on eBay than you could count. Most of them are easy to use; a few seem to be intended for larger pieces of equipment and can be a little clumsy to connect to or find useful drawings and specifications. But the prices can't be beat.

Don't forget that most of these inexpensive experimenter items are mailed via ship from Asia. Expect a 6-week delivery window.