[Mariano] owns a late 90’s Jeep Wrangler, and had no idea just how easy it was to steal. Unfortunately for him, the guy who made off with his Jeep was well aware of the car’s vulnerabilities. The problem lies in the ignition – it can be broken out with a screwdriver, after which, the car can be started with a single finger. How’s that for security?
[Mariano] decided that he would take matters into his own hands and add a remote-controlled switch to his car in order to encourage the next would-be thief to move on to an easier target. He describes his creation as a “remote kill” switch, though it’s more of a “remote enable” switch, enabling the engine when he wants to start the car rather than killing it on command.
The switch system is made up of two pieces – a server inside the car’s engine bay, and a remote key fob. The server and the fob speak to one another using IPv6 over 802.15.4 (the same standard used by ZigBee modules). Once the server receives a GET request from the key fob, it authenticates the user with a 128-bit AES challenge/response session, allowing the car to be started.
It is not the simplest way of adding a remote-kill switch to a car, but we like it. Unless the next potential car thief digs under the hood for a while, we’re pretty sure [Mariano’s] car will be safe for quite some time.
[Chris] over at the New Hobbyist sent in his latest creation, a wireless light switch hidden within a statue bust. While shopping around for another project, he came across a wireless relay that can can be used to switch a standard 120v AC load. He bought the part without a project in mind, but inspiration quickly struck. Some of you young’uns might not remember the original Batman television series, but [Chris] certainly does. To access the Bat Cave, Bruce Wayne had to flip a secret switch located inside a bust of William Shakespeare that adorned his desk. While he doesn’t have a secret door to activate, [Chris] couldn’t think of any better way to switch on the lights in his man cave. He found a similar-looking bust of Beethoven and got to chopping his head off.
He fabricated a small mount for a push button, hiding the battery powered remote underneath, and an old 12v wall wart was repurposed to drive the wireless receiver. While not overly complicated, this is definitely a fun project and could make for a neat light switch in a kid’s room. Interested in some more Batman inspired hacks? Be sure to check out this Bat Cave-style entrance switch from a few years back.
Keep reading to see a video of his hidden light switch in action.
Continue reading “Batman inspired hidden light switch”
This collection of touch sensor information should be of interest to anyone who liked the simple touch sensor post from Thursday. That was a resistive touch sensor and is covered in detail along with AC hum sensors that trigger based on induced current from power lines around you, and capacitive touch switches like we’ve seen in past hacks. Each different concept is discussed and clearly illustrated like the slide above. [Giorgos Lazaridis] has also put together individual posts that build and demonstrate the circuits. We’ve embedded his resistive sensor demo video after the break and linked to all three example circuits.
Continue reading “Touch sensors: overview, theory, and construction”
Wanting to save space and weight on his project build [Florin] set out to find a way to add Ethernet connectivity without the magnetics. His ill-advised first try involved directly coupling two switches, frying both in the process. After some research he found that Ethernet hardware manufacturers have considered the need for devices without the magnetics and there are several application notes available on the subject. [Florin] followed the information that Realtek has for their devices and learned that they can be couple capacitively. After depopulating the magnetics from a second pair of switches he wired up some resistor-capacitor networks on a breadboard and got the connecting to work.
[Patman2700] has a nice scope for his paintball gun that uses a red dot instead of cross-hairs. The problem is that he kept forgetting to turn it off which ended up running the batteries down frequently. His solution to the problem was to get rid of the toggle switch used to turn it on and replace it will a home-made momentary push button switch. Now he presses the switch to aim and doesn’t waste juice when he’s running around, trying not to get pelted with paint.
Since this is used outside he wanted it to be water-tight. The switch is built using materials we’ve seen in previous diy switches; adhesive-backed copper sheets for conductors, foam to keep them separated until pressed, and plastic as a support. Copper is applied to the plastic base, with a ring of foam separating the base from the second layer of copper. When squeezed, the two layers of copper come in contact to complete the circuit. To make it work a bit better [Patman2700] added a dab of solder in the center of the bottom copper layer so there is less distance between conductors, and used extra foam to build up a bump in the center of the assembly for a better ‘button’ feel. The whole thing is encased in shrink-wrap with the seams sealed with super glue to keep moisture at bay.
If you’ve ever designed an embedded system with at least one button you’ve had to deal with button debouncing. This is also know as contact bounce, a phenomenon where a button press can be registered as multiple button presses if not handled correctly. One way to take care of this is with a hardware filter built from a resistor-capacitor setup, or by using a couple of NAND gates. We find that [Jack Ganssle] put together the most comprehensive and approachable look at contact bounce which you should read through if you want to learn more.
We’re interested in software solutions for debouncing buttons. This seems to be one of the most common forum questions but it can be hard to find answers in the form of reliable code examples. Do you have debounce code that you depend on in every application? Are you willing to share it with the world? We’d like to gather as many examples as possible and publish them in one-post-to-rule-them-all.
Here’s some guidelines to follow:
- Please only include debounce code. Get rid of other unrelated functions/etc.
- You should send C code. If you want to also send an assembly code version that’s fine, but it must be supplementary to the C code.
- Please comment your code. This will help others understand and use it. You may be tempted to explain the code in your email but this info is best placed in the code comments
- Cite your sources. If you adapted this code from someone else’s please include a note about that in the code comments.
As an example we’ve included one of our favorite sets of debounce code after the break. Please note how it follows the guidelines listed above.
Continue reading “Open Call: send us your Debounce code”
Forget hacking an easy button, grab a couple of those outdated CD-Rs and build your own switch for that next project. This was developed with handicapped accessibility in mind; assembled easily with common products and it’s fairly robust. In fact, our junk box has everything you need except the adhesive backed copper foil. Combine two old CD’s, covered in copper on facing sides, separated by two strips of Velcro to separate the conductors. When pressure is applied, one CD flexes to make contact with the other and complete the circuit. So easy, yet we never thought of it. We’ll add it to our list of homebrew input devices.