Making the electronics for a Doppler motion sensor

There are many different sensors that can be used to detect motion in a given environment. Passive InfraRed (PIR) sensors are the most used today, as they work by detecting moving heat signatures. However, they are less reliable in the hotter days and obviously only work for animals and humans.

Sensors like the one shown in the above picture started to appear on the internet, they use the doppler effect to detect motion. I (limpkin) designed the electronics you need to add in order to get them to work.

Here is a simple explanation of the doppler effect: if you send an RF signal at a given frequency to a moving target, the reflected signal’s frequency will be shifted. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession. [Read more...]

SenseLamp automates rooms by replacing light fixtures


Would you believe that this beautiful light fixture is actually a hacked together home automation project? Okay, so this wire mess is the second of three versions that [Christian] built. It replaces a light fixture in the room, but if you look closely you’ll see that there is a compact fluorescent bulb included in the build. The laser-cut frame acts as a bit of a lamp shade, while providing a place to mount the rest of the hardware.

The final version cleans things up a bit, and adds a footprint for the PIR motion sensor that he forgot to design into this version. The idea is that each lamp monitors motion in the room, switching the light on and off again as necessary. A light-dependent resistor ensures that the bulb is only powered up if the room is dark so as not to waste electricity during the day.

The build includes a sensor package that reports back temperature and humidity data. Communications are provided by a WR703N router rolled into each of the four units installed in his house. With this kind of hardware at his disposal it should be a snap to control every IR remote control device in his house via the network by adding an IR LED and some code to the lamps.

Nerf Sentry Gun for the Apocalypse


If you’ve ever wanted to shoot someone with a Nerf gun, but just didn’t have the energy to get off the couch, this hack may be for you. It’s also a good way to ward off zombies if another apocalypse, Mayan or otherwise, is on the horizon.

Although the effects are very cool, as seen in the video after the break, the method for making this setup was quite simple. The requirements for this project were that the gun could not be permanently modified, and everything had to fire automatically. These restrictions may have contributed to the simplicity of the design as many of us would start breaking things before we had to.

Instead of some elaborate hack, the trigger was tied back in the firing position at all times. A relay was then used to interrupt the power supply to the mechanism allowing an Arduino equipped with an infrared sensor to automatically control the firing. The setup is explained after the break, but skip to around 1:55 if you’d rather just see the guns in action. [Read more...]

An umbrella stand that tells you the weather forecast

This project takes an umbrella stand and gives it the ability to let you know if you need to take an umbrella when you leave the house. The image above is a concept drawing, but a first prototype was built and seems to work quite well. See for yourself in the video after the break.

The project was put together by openPicus. They sell a prototyping module called the Flyport which provides a WiFi connection to your projects. This board connects to a set of LEDs which are used to illuminate the translucent plastic umbrella stand. But you might not notice the color change if the LEDs were always on. Also designed into the system is a PIR motion sensor. When you walk toward the door to leave for the day it switches on the appropriate color — green for clear, blue for raining, and red for storming — catching your attention in time to grab an umbrella as you pass by.

You don’t need to spend a bundle to pull off a hack like this. You can scavenge for a PIR sensor, use one color of LEDs just to tell you when rain or storms are forecast, and an ENC28J60 is a cheap and easy Ethernet alternative to using WiFi.

[Read more...]

Motion sensing fog machine

Our favorite holiday is just around the corner, so there’s no surprise in seeing a few builds to scare children turning up in the tip jar. [Greg] also loves Halloween and apparently puts on a good show – he always uses a fog machine on his porch on All Hallow’s Eve, but triggering it at the right time is always a pain.

This year, [Greg] decided to build a motion-sensing fog machine. His machine featured a wired remote with a light to signal when the fog machine is ready and a button to start the pump. This remote runs at 120V AC, but [Greg] figured he could stick a small USB phone charger in the remote and power an ATtiny85 microcontroller.

The actual circuit is just a piece of perfboard, a large, old relay from Sparkfun, and a PIR sensor [Greg] picked up last year. Whenever the PIR detects movement, the Tiny85 activates the fog machine for 5 seconds and disarms itself for another 10, until it sees movement again. Just the thing for a little interactive ambiance for [Greg]‘s Halloween display.

Video after the break.

[Read more...]

Another Automatic Air Freshener Use


We’ve seen air fresheners used for many hacks here at hackaday. This one is a bit different as it uses the PIR sensor assembly to turn on LEDs in sequence, rather than reversing a motor. Generally, the motor would be reversed by the fact that this assembly is reversing the voltage on a motor (see [H Bridge] on Wikipedia), but instead it turns on one set of LEDs and then the other.

This works because a diode (the “D” in LED) only allows current to flow one way. The LEDs are reversed with respect to the voltage source, making them come on in sequence. An Arduino or other microprocessor could of course be used to accomplish the same thing (see this [HAD] post about harvesting the PIR sensor only). However, if you had $10 or less to start your hardware hacking career, this is yet another way an air freshener can be hacked up to do your bidding.

Be sure to see the video of this simple hack after the break, used to “LED-ify” a Star Wars AT-ST painting. If you’re interested in using the gears and motor of an air fresher as well, why not check out this post on remotely triggering a camera with the internals from a time-based model? [Read more...]

Dual PIR photo trigger by crossing the streams

Motion sensing can be quite effective when taking photographs of wildlife. But how can one be sure that the motion was at the center of the frame? A PIR sensor picks up motion in its entire viewing range. It’s not really something that can be aimed. But if you use two PIR sensors you can monitor a focused area for motion.

The trick is to use a logic circuit. By building an AND gate you can trigger based on motion in the area which is overlapped by both of the sensors. In this case the AND gate is built from a voltage divider. The outputs of the PIR sensors are connected above and below the divider’s connection to the photo trigger. Both have a protection diode, and the divider is tuned so that both PIR outputs must come one in order to raise the trigger input above the voltage threshold. So much for never crossing the streams.

[via TriggerTrap]