Anyone who had a cheap set of computer speakers in the early 2000s has heard it – the rhythmic dit-da-dit-dit of a GSM phone pinging a cell tower once an hour or so. [153armstrong] has a write up on how to capture this on your computer.
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?
Before the AdLib sound card, sound on PCs was in a terrible shape. Since the dawn of IBM, all PCs included a speaker, but this PC speaker was only capable of sounding one note at a time. Chords on the PC speaker produced a weird ‘bubbling’ effect. Just a few years later, 8-bit sound could be created with the Covox Speech Thing, effectively a resistor ladder, with the parallel port on one side, and an 1/8″ plug on the other. These solutions for PC sound sucked.
It wasn’t until the first AdLib cards that superior sound showed up on the PC. Recently, [eric] had been fixing up an old IBM XT and quickly realized the original AdLib sound cards were collector’s items and far too expensive for what they were. He decided to build a reproduction Ad Lib. completely compatible and nearly identical to the original 1990 version of the best sound card on the market.
The first Ad Lib sound card is a relatively simple circuit based on the Yamaha YM3012 (OPL2) and YM3014B chips. These chips are frequently available on eBay, and [Sergey] already has a complete circuit for turning these chips into an ISA sound card. While this modern card is compatible with the AdLib Music Synthesizer Card, it doesn’t look like one. [eric] wanted a card that looked like the real thing, and sounded like one, too.
PCB design has come a long way in a generation, and where the AdLib card was once a wonder of modern technology, anyone with enough patience can now design an identical board, send the file off to China, and receive a reproduction of the first successful sound card. All the files are up on Github should you want to build your own. Now all we need is someone making modern 486 motherboards.
Using the inputs on a computer’s sound card is an old trick to fake a very simplistic, AC coupled, slow oscilloscope. You can get DC operation by desoldering a couple capacitors, but if the sound card is integrated into the motherboard it raises the stakes if you mess that up.
[TMSZ] has a better option, a ~1 dollar USB sound card which is easily hacked to work as a simple oscilloscope. Easily found on eBay, the 7.1 virtual channel sound card is identical in brains to a more expensive c-media model, but the layout of the PCB makes it easier to bypass the DC blocking caps. Software and DLL files to use the sound card with Miniscope v4 — a Windows GUI for oscilloscopes — are also linked, so getting set up should be fairly simple.
Now of course this is not lab-grade measurement equipment: the sampling rate is limited to 44KHz and the voltages must be in the typical “line level” range, under two volts. If you don’t mind a little extra noise, you can increase the input impedance with a single resistor. This extends the input range up to six volts, which covers most hobby and microcontroller usage.
So if you’re really in need of a scope, but only have a buck to spend, this may be just the hack for you! Those willing to shell out a hefty sum for a high-end headless oscilloscope should look onto the virtual bench.
Before the days when computers could play and record audio that far surpassed the quality of CDs, sound cards were very, very cool. Most audio chips from the 80s, from the Commodore SID is pretty much a synth on a chip, but you can also find similar setups in ancient ISA sound cards. [Emilio] pulled one of these cards with an ADLIB OPL2 chip on it, and used a PIC micro to create his very own FM synthesis synth (IT, translatatron, although Google is screwing up the formatting).
The Yamaha YM3812 chip, otherwise known as the OPL2, was a fairly complete synthesizer in a very tiny package using FM synthesis for some very unique sounds. Once [Emilio] had the PIC sending commands to the sound chip, he added MIDI support, allowing him to play this vintage ‘synth on a chip’ with a keyboard instead of a tracker.
Judging from the video below, it sounds great, and that’s with [Emilio] mashing the keys for a simple demo.
Continue reading “MIDI And Vintage FM Synthesis”
Are you interested in building a 20kHz 2-channel oscilloscope and a 2-channel signal generator for only $20 with minimal effort? Be sure to check out [Jan_Henrik’s] Instructable that goes over how to build this awesome tool from a cheap USB audio card.
We have featured tons and tons of DIY oscilloscopes in the past, but this effort resulted in something very well put together while remaining very simple to understand and easy to build. You don’t even need to modify the USB audio card at all. One of the coolest parts of this build is that you can unplug your probe assembly from your USB audio card, and bring it wherever your hacking takes you. After the build, all you need is [Christian Zeitnitz’s] Soundcard Oscilloscope program and you are good to go. One of the major downsides that is often overlooked when using an audio based oscilloscope, is that it is “AC coupled”. This means you cannot measure low-frequencies (including DC signals) using a sound card. Be sure to heed [Jan_Henrik’s] advice and do not use your built in audio card as an oscilloscope. With no protection circuitry, it is a sure fire way to fry your computer.
What analog projects have you built around an audio interface? We have seen such an interface used for many different applications, including a few fun medical related hacks (be sure to keep safety your first priority). Write in and let us know!
[Entropia] decided to try his hand at rolling is own sound card. He picked out a DAC chip, started his prototyping by studying the reference design from the datasheet, then went through several iterations to arrive at this working model.
He chose to base the board around the PCM2706. It’s a digital to analog converter that has built-in USB support; perfect for his needs. It’s got a headphone amplifier, but is also capable of putting out S/PDIF signals for a digital amplifier to pick up and use. Not bad for a part that can be had for right around eight bucks.
The first PCB he designed had a few electrical and footprint errors. But he was able to get it to run by adding some point-to-point jumpers, and bending the legs of his capacitors to fit the board area. With those issued accounted for he ordered a second batch of boards. These went together nicely, but the headphone output was incredibly loud. Turns out the filtering circuit had the wrong resistor and capacitor values. Changing them around, and swapping the audio output so that the correct channels were patched to the audio jack brings it to the first release version seen above.
[Darrell] is using a sound card to drive this servo motor. The motor draws power from a cellphone battery with the control signal coming from one of the audio channels. It’s not too surprising that this works since the motor just needs a PWM signal to operate and that’s what is used to create the different frequencies of sound on electronic speakers. We’re not sure what [Darrell’s] got planned for this system but he mentions that two servos can be used, one on each audio channel. If you’re not using your sound card this would be a way to stop using the Arduino for that mail checker and just use a little flag attached to a servo. When mail comes in the appropriately engineered sound raises the flag.