Step 1: Parts and Tools
- Philips Spot-On Motion activated LED lamp (or similar)
- Multi - turn trimmer pot (optional)
- Laser diode module (preferably high power >10mW, any color)
- ~15mm focal length miniature lens (optional)
- Laser printer acetate film
- Record-your-own-message greetings card, or just the sound module out of one
- FM music transmitter
- 3 x AAA battery box
- Altoids tin or other enclosure
- Soldering iron
- Desoldering vacuum
- Dremmel or other multitool (for customising the enclosure)
- Junior hacksaw
- Access to a laser printer or photocopier
Step 2: Motion Detector (1 of 3)
Begin by unscrewing the back panel and exposing the circuit board. Remove the batteries and wiggle the board to free the battery contacts on either side and the board should slide right out of the casing.
Step 3: Motion Detector (2 of 3)
- Desolder the battery contacts using a desoldering vacuum
- Desolder the three LEDs in the same way
You can keep the 3mm white LEDs for another project, and solder on a 3xAA or 3xAAA battery box at this point if you like.
The LEDs on this lamp are cathode switched, meaning that the transistor responsible for turning them on is connected to the cathode pins of the LEDs. The anodes are connected essentially straight to the +ve battery supply through a series resistor to control the current passing through them. For this reason, we'll be using the cathode pads for the LEDs to switch the different parts of our system on when the sensor triggers.
I decided I wanted to be able to alter the on time of the system as the on time that's set by default is quite long. I picked up a copy of the chip used on the board (it's a BISS0001, datasheet is here if you want to take a look). By a process of deduction and following the traces on the PCB, it turned out that R18 was the resistor I needed to change in order to alter the on time. I replaced it with a multiturn precision pot (1K 10 turn I think), which is easily available and pretty cheap from any electronics hobbyist shop. That way, I could adjust the on time until I was happy with it.
Step 4: Motion Detector (3 of 3)
Step 5: Laser Projector (1 of 5)
The diode I used was ripped from a 15x DVD writer and is capable of putting out over 100mW of light at 650nm, which is a nice ruby red. A word of caution:
BEWARE WHEN USING HIGH POWER LASER DIODES!! The amount of light they put out at their peak is decidedly dangerous to your sight and that of those around you!!
The beam of the laser in this project will be expanded to such an extent that it will be eye-safe once complete, but be super careful about knowing where the beam is pointing when you power it up until it's safely expanded.
For the purposes of this project, I just used a simple resistor to stop my diode from blowing up when connected to the 4.5V power supply, but you can buy modules already housed with a collimating lens and driver if you so desire. DO NOT under any circumstances connect your diode directly to the batteries! That is a one way ticket to laser diode burnout.
Step 6: Laser Projector (2 of 5)
The lens I used had a focal length of around 15mm and was pulled out of the same DVD writer that the diode came from. I glued it straight to the front of the laser module with a few dabs of hot glue, trying my best not to get any glue in the path of the beam itself.
I had to unscrew the rear portion of the module housing to give enough distance within the Altoids tin for the beam to expand.
Step 7: Laser Projector (3 of 5)
I did my modifications with a Dremmel and a diamond cutting disc attachment, but there are many other ways to do it.
Step 8: Laser Projector (4 of 5)
The images were trimmed close around three of the sides, but the third side had an extra piece of acetate left on with a small tab at the top and bottom (sort of a fat 'T' shape overall). The tabs can then be slotted into the slots that were left in the tin to hold the image in place, and allow for easy adjustment or swapping out for a different image later. You will need to flex the acetate image to allow the tabs to slide into the two slots. When you close the lid of the tin, if you tuck in the top tab so that it goes under the lid, this will help to keep the image in place even more securely.
Step 9: Laser Projector (5 of 5)
Step 10: Audio Transmitter (1 of 2)
The first thing to do is get the boards out of their respective enclosures. The audio recording module is easy, but the transmitter might be harder depending on how well it's sealed inside whatever enclosure it came in. In the case of the audio module I used, I was able to remove the entire section of the PCB that held the batteries and solder wires to carry power to the board, which reduced the size significantly.
In the case of the FM transmitter, the mini USB and audio jack were desoldered and wires soldered on in their place, and a couple of sections were removed with a hacksaw to reduce the size a little. In the case of the transmitter I used, the shield connection of the audio jack was also the aerial connection for the transmitter (the shield of the audio cable acted as the aerial).
Step 11: Audio Transmitter (2 of 2)
As far as the transmitter was concerned, I wasn't keen to have a long aerial wore trailing out of the tin, and it couldn't be hidden inside as the tin completely shields the signal. The solution I settled upon (which is decidedly non-optimal, but it works), was to solder a wire connecting the ground connection of the audio input (which doubled as the aerial connection) to the tin itself, so that the tin became the aerial. This works surprisingly well, although the range is reduced a little.
Step 12: Putting It All Together
The audio module was left with all buttons, the microphone and record LED in place so that the box can be repurposed by recording a different message and changing the acetate image. The module and all it's associated bits fit quite snugly in the remaining space in the tin.Take a look at the image of the final layout to see how it all fits together.
I would advise that wires are kept as short as possible, as they have a knack of finding their way into the hinge and getting pinched if you're not careful.
Step 13: Finishing Up
Below is a video of the box from a victim's perspective. It looks somewhat brighter in person, but you get the jist!
I hope you find something of worth in this little project, and please hit the comments if you have any questions!