[Simon] has been using his home alarm system for over six years now. The system originally came with a small RF remote control, but after years of use and abuse it was finally falling apart. After searching for replacement parts online, he found that his alarm system is the “old” model and remotes are no longer available for purchase. The new system had similar RF remotes, but supposedly they were not compatible. He decided to dig in and fix his remote himself.
He cracked open the remote’s case and found an 8-pin chip labeled HCS300. This chip handles all of the remote’s functions, including reading the buttons, flashing the LED, and providing encoded output to the 433MHz transmitter. The HCS300 also uses KeeLoq technology to protect the data transmission with a rolling code. [Simon] did some research online and found the thew new alarm system’s remotes also use the same KeeLoq technology. On a hunch, he went ahead and ordered two of the newer model remotes.
He tried pairing them up with his receiver but of course it couldn’t be that simple. After opening up the new remote he found that it also used the HCS300 chip. That was a good sign. The manufacturer states that each remote is programmed with a secret 64-bit manufacturer’s code. This acts as the encryption key, so [Simon] would have to somehow crack the key on his original chip and re-program the new chip with the old key. Or he could take the simpler path and swap chips.
A hot air gun made short work of the de-soldering and soon enough the chips were in place. Unfortunately, the chips have different pinouts, so [Simon] had to cut a few traces and fix them with jumper wire. With the case back together and the buttons in place, he gave it a test. It worked. Who needs to upgrade their entire alarm system when you can just hack the remote?
Bode plots – or frequency response graphs – are found in just about every piece of literature for high-end audio equipment. It’s a simple idea, graphing frequency over amplitude, but making one of these graphs at home usually means using a soundcard, an Excel spreadsheet and a multimeter, or some other inelegant solution. Following a neat tutorial from [Dave Jones], [Andrew] came up with a very simple way to make a Bode plot in real-time with an oscilloscope, a microcontroller, and a few off-the-shelf parts.
The basic idea behind [Dave Jones]’ impromptu Bode plotter is to configure a frequency generator to output a sine wave that ramps up over a period of time. Feed this sine wave through a filter, and you have amplitude on the vertical axis of your ‘scope and frequency on the horizontal axis. Boom, there’s your Bode plot.
[Andrew] did [Dave] one better by creating a small circuit with an Arduino and an AD9850 sine wave generator. Properly programmed, the AD9850 can ramp up the frequency of a sine wave with the Arduino outputting sync pulses every decade or octave of frequency, depending if you want a linear or log Bode plot.
It’s a nifty little tool, and when it comes to building test equipment from stuff that just happens to by lying around, we’ve got to give it up for [Andrew] for his really cool implementation.
[Keith] got his hands on a few grandfather clocks. Apparently the price tag is greatly reduced if you are able to get them second-hand. The mechanical timepieces require weekly winding, which is a good thing since you’ll also need to correct the time at least that often. But this drift got [Keith] thinking about improving the accuracy of these clocks. He figured out a high-tech way to adjust the timepiece while it’s ticking.
The first thing he needed was a source of super-accurate time. He could have used a temperature compensated RTC chip, but instead went the more traditional route of using the frequency of mains power as a reference. The next part of the puzzle is to figure out how to both monitor the grandfather clock and make small tweaks to its pendulum.
The answer is magnets. By adding a magnet to the bottom of the pendulum, and adjusting the proximity of a metal plate positioned below it, he can speed up or slow down the ticking. The addition of a hall effect sensor lets the Arduino measure the rate of each swing and calculate the accuracy compared to the high voltage frequency reference.
Check out this nice simple method of achieving a 1Hz timebase. This is basically a lesson in dividing crystal frequencies in circuits to get the desired result. In this case, they are starting with a 32.768KHz crystal and dividing it down. Instead of using an NE555 like many projects, he chose to go a direction that would yield results less prone to drifting with temperature variation. The method chosen was a CD4060 frequency divider, basically just a chain of flipflops. The divider is one step short of getting to the desired result so an additional flipflop has to be added. This is pretty basic stuff, but a great read. They go into detail as to how it all works and why you would use this method.
Pssst, hey, remember that time I told you to just use a 1Hz crystal? yeah, we can laugh at that again.
[Charlie X-Ray] is having some modern fun with the phone system by pulling dialed numbers from the audio track of YouTube videos (translated). The first step was to find a video where a telephone is being dialed and the sounds of the keypresses are audible. You can’t tell those tones apart, but a computer can. That’s because each number pressed generates a combination of two out of seven closely related frequencies. [Charlie] isolated the audio using Audacity, then wrote a python script to generate a spectrogram like the one above. By matching up the two dark nodes you can establish which two frequencies were played and decode the phone number being dialed. So how does this work again… find audio of a phone being dialed, decode the number.. profit?
[Emmanuel Roussel] is coding a version of Tetris for the IM-ME. Before you get too excited, he hasn’t actually written the game yet, but instead started with the familiar theme music. The IM-ME has a piezo speak on board so it’s just a question of frequency and duration. [Emmanuel] developed an Open Office spread sheet that calculates each note’s frequency and the timer value needed to produce it. He then created a data type that stores a note and its duration and used an array of those structures to store the song. If you’ve ever wondered how to cleanly code music this is a wonderful example to learn from because right now the code doesn’t have anything other than that code to get in the way.
The ground work for this was established in the other hacks we’ve seen. Now we’re left wondering who will finish coding their game first. Will it be [Emmanuel’s] Tetris or [Travis’] Zombie Gotcha?
The back story behind [Mike] experimenting with plants as AM radio transmission antennas antennae is rather interesting and worth the short read. But for those who just want the facts, [Mike] took an ATMega324, modified the PWM output into a sinusoidal AM signal (using a simple form of RLC circuitry), and connected the circuit to a plant no plants were harmed in the making of this project. The results? Well we’re not ones who would spoil the surprise, you’ll have to see for yourself in the video after the jump.
Continue reading “Plantenna: the plant antenna”