It’s incredibly simple to do – simply plug in a set of headphone to the sound card’s microphone jack, leave a mobile phone nearby, hit record, and wait. The headphone wire acts as an antenna, and when the phone transmits, it induces a current in the wire, which is picked up by the soundcard.
[153armstrong] notes that their setup only seems to pick up signals from 2G phones, likely using GSM. It doesn’t seem to pick up anything from 3G or 4G phones. We’d wager this is due to the difference in the way different cellular technologies transmit – let us know what you think in the comments.
This system is useful as a way to detect a transmitting phone at close range, however due to the limited bandwidth of a computer soundcard, it is in no way capable of actually decoding the transmissions. As far as other experiments go, why not use your soundcard to detect lightning?
If you are interested in electronics or engineering, you’ll have noticed a host of useful-sounding apps to help you in your design and build work. There are calculators, design aids, and somewhat intriguingly, apps that claim to offer an entire instrument on your phone. A few of them are produced to support external third-party USB instrument peripherals, but most of them claim to offer the functionality using just the hardware within the phone. Why buy an expensive oscilloscope, spectrum analyzer, or signal generator, when you can simply download one for free?
Those who celebrate Christmas somewhere with a British tradition are familiar with Christmas crackers and the oft-disappointing novelties they contain. Non-Brits are no doubt lost at this point… the crackers in question are a cardboard tube wrapped in shiny paper drawn tight over each end of it. The idea is that two people pull on the ends of the paper, and when it comes apart out drops a toy or novelty. It’s something like the prize in a Cracker Jack Box.
Engineering-oriented apps follow this cycle of hope and disappointment. But there are occasional exceptions. Let’s tour some of the good and the bad together, shall we?
It was one of the more interesting consumer tech stories floating around at the turn of the century, a disposable cell phone manufactured using a multi-layer folded paper circuit board with tracks printed in conductive ink. Its feature set was basic even by the standards of the day in that it had no display and its only function was to make calls, but with a target price of only $10 that didn’t matter. It was the brainchild of a prolific New Jersey based inventor, and it was intended to be the first in a series of paper electronic devices using the same technology including phones with built-in credit card payment ability and a basic laptop model.
The idea of a $10 mobile phone does not seem remarkable today, it’s possible that sum might now secure you something with features far in excess of the Nokias and similar that were the order of the day at that time. But when you consider that those Nokias could have prices well into three figures without a contract, and that the new features people considered exciting were things like integrated antennas or swappable coloured plastic covers rather than the multicore processors or high-res cameras we’re used to today, a phone so cheap as to be disposable promised to be very disruptive.
The product’s wonderfully dated website (Wayback Machine link, we’ve skipped the Flash intro for you) has pictures of the device, and the video below the break features shots of it in use as its inventor is interviewed. But by the end of 2002 the Wayback Machine was retrieving 404 errors from the server, and little more was heard of the product. No sign of one ever came our way; did any make it to market, and did you have one?
With the benefit of fifteen years hindsight, why did we not have paper mobile phones as part of the ephemera of the early years of the last decade? It was not a product without promise; a ten-dollar phone might have been a great success. And the description of a cheap laptop that talks to a remote server for its software sounds not unlike today’s Chromebooks.
Some of you might claim the product was vapourware, but given that they demonstrated a working prototype we’d hesitate to go that far. The likelihood is that it did not find the required combination of component price and manufacturing ease to exploit its intended market segment before its competition improved to the point that it could no longer compete. If you have ever taken apart a typical mobile phone of the period you’ll have some idea of why they were not cheap devices, for example the RF filter modules of the day were individually adjusted precision components. And paper-and-ink printed circuit boards are still a technology with a way to go even now, perhaps the idea was simply too far ahead of its time. Meanwhile within a relatively short period of time the price of simple candybar phones dropped to the point at which they would tempt the $10 buyer to spend more for a better product, so the window of opportunity had passed.
CMOS imaging chips have been steadily improving, their cost and performance being driven by the highly competitive smartphone industry. As CMOS sensors get better and cheaper, they get more interesting for hacker lab projects. In this post I’m going to demonstrate a few applications of the high-resolution sensor that you’ve already got in your pocket — or wherever you store your cell phone.
CMOS vs CCD
First lets quickly review image sensors. You’ve probably head of CMOS and CCD sensors, but what’s the difference exactly?
As the figure above shows, CCD and CMOS sensors are both basically photodiode arrays. Photons that hit regions on the chip are converted into a charge by a photodiode. The difference is in how this charge in shoved around. CCD sensors are analogue devices, the charge is shifted through the chip and out to a single amplifier. CMOS sensors have amplifiers embedded in each cell and also generally include on-chip analogue to digital conversion allowing complete “camera-on-a-chip” solutions.
Because CMOS sensors amplify and move the signal into the digital domain sooner, they can use cheaper manufacturing processes allowing lower-cost imaging chips to be developed. Traditionally they’ve also had a number of disadvantages however, because more circuitry is included in each cell, less space is left to collect light. And because multiple amplifiers are used, it’s harder to get consistent images due to slight fabrication differences between the amplifiers in each cell. Until recently CMOS sensors were considered a low-end option. While CCD sensors (and usually large cooled CCD sensors) are still often preferred for scientific applications with big budgets, CMOS sensors have now however gained in-roads in high performance DSLRs.
[Seandavid010] recently purchased a 2004 Volvo. He really liked the car except for the fact that it was missing some more modern features. He didn’t come stock with any navigation system or Bluetooth capabilities. After adding Bluetooth functionality to the stock stereo himself, he realized he would need a secure location to place his iPhone. This would allow him to control the stereo or use the navigation functions with ease. He ended up building a custom iPhone mount in just a single afternoon.
The key to this project is that the Volvo has an empty pocket on the left side of the stereo. It’s an oddly shaped vertical pocket that doesn’t seem to have any real use. [Seandavid010] decided this would be the perfect place to mount his phone. The only problem was that he didn’t want to make any permanent changes to his car. This meant no drilling into the dash and no gluing.
[Seandavid010] started by lining the pocket with blue masking tape. He then added an additional lining of plastic wrap. All of this was to protect the dashboard from what was to come next. He filled about half of the pocket with epoxy putty. We’ve seen this stuff used before in a similar project. He left a small opening in the middle with a thick washer mounted perpendicular to the ground. The washer would provide a place for an off-the-shelf iPhone holder to mount onto. [Seandavid010] also placed a flat, wooden paint stirrer underneath the putty. This created a pocket that would allow him to route cables and adapters underneath this new mount.
After letting the epoxy putty cure for an hour, he removed the block from the pocket. The stick was then removed, and any gaps were filled in with putty. The whole block was trimmed and smooth down for a more streamlined look. Finally, it was painted over with some flat black spray paint to match the color of the dashboard. An aftermarket iPhone holder allows [Seandavid010] to mount his cell phone to this new bracket. The cell phone holder allows him to rotate the phone into portrait or landscape mode, and even is adjustable to accommodate different sized phones.
[Tim] drives a 1995 Mitsubishi TS Magna, which is equipped with a less than stellar accessory package he lovingly calls a “poverty pack”. He outfitted his ride with an aftermarket head unit that can support the Bluetooth A2DP profile, provided he buys the ridiculously overpriced kit sold by Pioneer. Reluctant to shell out more money on an audio kit than his car is worth, he whipped up his own Bluetooth kit for far less than Pioneer’s asking price.
He had a set of Nokia Bluetooth headphones that he was willing to part with, so he disassembled them to see how he might interface with his car stereo. Connecting the headset to his head unit was a relatively easy task, but he had to work a bit harder to get his Bluetooth receiver powered properly.
After both undervolting and then nearly cooking his wireless audio rig, [Tim] managed to get things operating to his liking. He says that the audio is a touch quieter than he would like at the moment, so he will likely be revising his design in the near future. For now however, he can stream tunes from his phone while he cruises around town.
[Dimitris] decided to build a homemade alarm system, but instead of triggering a siren, sending an SMS message, or Tweeting about an intrusion, he preferred that his system call him when there was trouble afoot. He says that he preferred a call over text messaging because there are no charges associated with the call if the recipient does not pick up the line, which is not the case with SMS.
The system is based around an off the shelf motion detector that was hacked to work with an old mobile phone. The motion detector originally triggered a siren, but he stripped out the speaker and wired it to a bare bones Arduino board he constructed. The Arduino was in turn connected to the serial port of an unused Ericssson T10s mobile phone. This allows the Arduino to call his mobile phone whenever the motion detector senses movement.
The system looks to be quite useful, and while [Dimitris] didn’t include all of the code he used, he says others should be able to replicate his work without too much trouble.