Posted by Matthew
I recently found a doorknob touch alarm schematic while browsing Discover Circuits’ archives. The project was originally intended as a present for my brother’s dorm room, but a bad capacitor and the lack of a proper oscilloscope caused delays. It has not made it off the breadboard, and it probably will not until his next semester. The circuit contains a few basic elements, an flip-flop based oscillator, a set of delays, a flip-flop as a sensor, and the audible alarm.
Posted by Matthew
Scouring the Internet for information on LEDs, I accidentally stumbled upon a PDF detailing a flashlight made from PVC. For the torch, he biases ultra-bright LEDs with ballast resistors as described in my LED lighting guide. This is a simple solution, but a with a slightly more complicated circuit we can extend battery life by over ten times!
Download PDF instructions for the inefficient version
Posted by Matthew
Theodore Gray, co-founder of Wolfram Research, Inc makers of Mathematica, wrote up an amazing article on making your own light bulb. The project is quick and simple, but a little pricey:
Edison’s first mistake was living before tungsten wire was available. Tungsten is way better than carbon as a filament material, and now you can find it in any metal-supply shop… His second mistake, repeated in classroom physics demonstrations to this day, was using a vacuum to get the air out of the bulb…
Posted by Matthew
Afraid the government is trying to track you? Want to disable your old credit cards wireless signal? Need to get that new backpack out of Macy’s without getting caught? You need to disable those RFID tags.
There are several ways to deactivate RFID-Tags. One that might be offered by the industries are RFID-deactivators, which will send the RFID-Tag to sleep. A problem with this method is, that it is not permanent… The RFID-Zapper solves this dilemma… It generates a strong electromagnetic field with a coil, which should be placed as near to the target RFID-Tag as possible. The RFID-Tag then will receive a strong shock of energy comparable with an EMP and some part of it will blow, thus deactivating the chip forever.
If this zapper was bigger, then I could mess up Wal*mart’s inventory for months.
Posted by Matthew
Lately the hoopla concerning LED lighting has been overwhelming. Everyone claims this costs mere pennies to power. I decided to put a new twist on a classic science experiment to prove that LEDs do cost pennies to power. Literally.
Posted by Matthew
Previously, E-DSP visited the possibility of using your sound card as a signal/function generator. I was curious about the results, but did not have a Windows machine close by to test it. After some searching, I found a Linux alternative and was able to test the limitations of my Sound Blaster Live!
Posted by Matthew
Makezine recently posted a diy lie detector kit that uses your skin resistance (aka sweat) to detect a lie. The kit is well explained and consists of two probes you place on your palm with a red/green led readout.
This is all well and good, but sometimes a little more feedback is a bit more intuitive. We are trying to learn here.
Some time ago, Jason Bradbury created his own lie detector using only a resistor, a transistor, an led, and a multimeter. The led lights up if you are lying, but the multimeter provides more precise feedback of the skin’s resistance.
If you are really desperate, you can just clip the leads of your multimeter straight to your subjects palm. The ‘scary’ device may cause them to sweat and ruin the experiment, though. Just don’t tell your girlfriend you will shock her if she does not love you.
The galvanic skin response sensor uses a LEGO RCX brick to detect lies and also has numeric feedback. The finger straps are the best part of this project. Your subject will know you mean business when you clip these puppies to your multimeter.
Posted by Matthew
The hard drive clock is quite possibly the best diy electronics paperweight I have come across. Even though it has no particular use, it is uber cool. The clock requires a PIC 16f628 microcontroller, and old hard disk, and some miscellaneous components.
Unfortunately, the design lacks a real time clock. After a few days, you’re going to be late. He also mentions adding a fancier hourly chime. Personally, I think an old school computer beep and some circling LEDs would be perfect.
Hopefully I can find some time to convert my old 800MB drive into a $300 clock. It would be perfect for my office because the bedroom is definitely out of consideration.
Posted by Matthew
DIYLive.net dug up a simple fm radio. ‘A good starter DIY project for anyone interested in audio.’
AM radio circuits and kits abound. Some work quite well. But, look around and you will find virtually no FM radio kits. Certainly, there are no simple FM radio kits… I have developed this simple radio kit. It is a remarkable circuit. It is sensitive, selective, and has enough audio drive for an earphone.
Posted by Matthew
Justin describes how to build a DIY four part motor. It requires a battery, a wire, a screw, and a small disc magnet. The hardest part is getting the screw to hang from the battery.
The way this motor works (as shown below) is by creating a closed circuit, where the current actually flows through the magnet. When this happens, a magnetic force turns the magnet, which spins the screw.
He also posted a Google video of the motor in action. This project has always been great for procrastination or entertaining youngsters.
