DIY Live » Audio

DIY Spy Ear reverse engineering

Greg Lipscomb — Mon, 13 Aug 2007 18:02:14 +0000

Here is a project that I have often thought of. I hope we have all seen those amplifier spy toys for like a dollar. I have often thought of grabbing one, and using the circuit to make something cool. It would probably work as a headphones amplifier. You could even stick it into an altoids can. I am not sure if it would power a larger speaker, but I bet you could push it a little. It would have to be modified, and I have not researched it. It seems that this device is using a filter to just pick up conversation ranges and filter out background noise. Some capacitors could be changed to make it HIFI. It would not be ideal but would work.

Now this Instructable actually does a little more than just use this circuit. He actually reverse engineers this project. It is a fairly simple circuit. All you really have to do to reverse engineer something is to make a list of the parts on the circuit board, and then follow all of the traces and see where they connect.

There are several ways of doing this. On a simple one or two layer board, you could simply visually follow the traces. You could also use a multimeter to find the connections. In this article, he actually takes a picture of the front and back. He then goes to photoshop and pulls of the traces on the back of the board. He flips it around, and places it on top of the front of the board. He then visually drew a circuit.

You can see the final circuit below. Article via Make

Simple FM Radio

Greg Lipscomb — Mon, 16 Jan 2006 02:06:51 +0000

Here is a perfect simple one transistor FM radio to build. Here is a good starter DIY project for anyone interested in audio. This simple radio uses an inductor as both the oscillator circuit and the antenna. It just uses one JFET transistor. There are two designs on this site. The first one is a circuit that will run a high impedance earphone, and another that will run regular headphones. This radio can be tuned by either changing the distance between the coils in the homemade inductor, or by turning the trimming capacitor. This changes the frequency oscillations, and tunes the radio to the correct FM frequency.

…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. The simple FM radio circuit got lost during the transition from vacuum tubes to transistors. In the late 1950s and early 1960s there were several construction articles on building a simple superregenerative FM radio. After exhaustive research into the early articles and some key assistance from a modern day guru in regenerative circuit design, I have developed this simple radio kit. It is a remarkable circuit. It is sensitive, selective, and has enough audio drive for an earphone…

Read more about this cool project at somerset.net

DIY Stereo FM transmitter 2

Greg Lipscomb — Sat, 14 Jan 2006 14:37:12 +0000

I recently told about the BA1404 stereo fm transmitter integrated circuit. It is the main chip that you find in most kits (I have done kits. They usually are solder by number, and don’t really teach you anything, unless you really study them, and are therefore not much fun. It is much better to do it yourself). The Griffin iTrip uses a similar chip to this. I mentioned that the quality of this chip is pretty poor. It does too much. It has the FM transmitter built inside. Everything is too close inside the chip, and there is crossover distortion. This chip is not even made anymore.

There is a much better option to the BA1404. The NJM2035 chip does not have a built in transmitter, or the FM oscillator. This chip takes the two inputs, which should be connected through a Pre-emphasis circuit. High frequencies in a FM system contribute to noise, so the pre-emphasis circuit increases the amplitude of the high frequencies before putting them into the chip. This chip takes the two inputs, and the input of a 38KHz crystal. This chip then creates a stereo composite signal and a 19KHz pilot signal. These two signals are mixed externally, and then an mono FM transmitter can be used. Check out my simple DIY FM transmitter for how-to information on building one. Check out the pdf on this chip to read more on how to use it.

DIY iPod stereo FM transmitter

Greg Lipscomb — Wed, 11 Jan 2006 05:16:11 +0000

After posting about the simple FM transmitter, I decided that I wanted to try to make a stereo transmitter for an iPod. Something like the Griffin iTrip. This would not have to be just for an iPod, but could be for basically any stereo signal that you wanted to send to a stereo. After seeing how simple the mono FM transmitter was, I thought it would not be that bad to do stereo, but I was really wrong. A stereo signal has to be modulated together and carried on a carrier frequency. Everything has to be perfect to make it work. It is a very daunting task, and I could not do it. After a quick google search, I kept running accross stereo FM transmitter kits, and a lot of the cheaper ones use the BA1404 integrated circuit stereo transmitter. I reseached this chip on diyaudio.com (This is a great forums to search for all sorts of DIY audio stuff). I found that it is not really that good of a transmitter, and has a lot of distortion, but I figure that for what I would like to do with it, it should be tolerable.

This is the schematic for the chip. This would have to be tested first, and then a PCB would have to be made. It would be nice if it could be made really small. I am just not sure how small it could be made. If you did not mind losing stereo capability, you could always just mix the two channels together, and use the mono transmitter. This chip is no longer made, but it can still be found at various places on the net. I found a supply of them at electronics-diy.com

The pdf file can be downloaded here[ba1404.pdf]

Decode telephone touch tone

Greg Lipscomb — Tue, 27 Dec 2005 21:43:54 +0000

Here is a quick cool thing to look at. I really want to design something using telephone touch tone. It is 2 frequencied combined to make the tone, and here is an article on getting a encoder and decoder. I will do better updates after the holidays. Things are crazy now, and I am at my parents house and on dialup. It is like going back in time Anyway, check out this article. It is very good.

…Dual-tone-multi-frequency (DTMF, also known as touch-tone) are the audible sounds you hear when you press keys on your phone…Touch-tone is familiar to many (telephone), it is a mature technology, and readily available with off-the-shelf, single-chip, low-cost components. For these reasons DTMF is often used in remote control applications that typically use telephones (e.g. accessing your messages from an answering machine, retrieving your account balance info from your bank’s database)….

[Link]

DIY FM transmitter

Greg Lipscomb — Wed, 21 Dec 2005 05:08:19 +0000

This is an article that I am very interested in. It is not so important to me to have the capability of using a microphone to transmit over FM, but, I want to try to build an FM transmitter to use as a remote control.

There are other uses of this circuit. It can be used to transmit any audio signal. It is basically the same as a Griffin iTrip. There is an inductor/capacitor oscillator that can be changed to change the transmitted frequency. It has a home made inductor, and a trimmer capacitor which can be changed to change the frequency. This project can be found at tacashi.tripod.com Article submitted by Utch

Altoids pocket amplifier

Greg Lipscomb — Sat, 05 Nov 2005 16:15:20 +0000

This project was featured on Makezine, only they did not show the article. It was just the Flickr pictures of it (at least that is the project I saw). This is a neat project to make, and has several applications. First it could just be to power your headphones, or it could power a small speaker. This is an integrated circuit amplifier, which like I said earlier is still basically a bunch of transistors in series. There are some differences though. This one uses capacitors. If you put a capacitor in series with your speaker, you will cut out any DC going into the speaker. This will make your battery last longer, and your speaker won’t get as hot. You can also use capacitors as a band pass filter. I will probably one day give a tutorial on using band pass filters in our simple 1 watt amplifier to make it more efficient. (Not now though, I have said that I am in medical school, and I have a hard microbiology test on monday, So I prob. won’t update in the next couple of days, but keep coming back, and we will discuss all the parts we need for a good amplifier). For now though, check out this site. [Tangentsoft.net]

Build your own Radio

Greg Lipscomb — Fri, 04 Nov 2005 00:16:53 +0000

If you look down a few articles and see the laser radio, you may wonder how can you transmit a radio signal through light? Well in reality, you are not sending a radio signal, because that is via an electromagnetic wave, but you are modulating the light. You are actually amplitude modulating the light (AM), just like an AM radio signal is amplitude modulating the e-mag wave. If you turn the light on and off at a constant frequency (and amplitude) of on once a second, then you have a frequency of 1 hz. Likewise 60 times a second is 60hz. This type of signal would produce a certain noise in a speaker. If you change the frequency, you change the pitch of the sound that you hear coming out of the speaker. The faster you turn the light on and off the higher the pitch.

Now if you turn the light on really bright once, and then turn it on really dim the next time, you are changing the amplitude. This tells the speaker how much force to move on each beat. By varying these two things, with the light, you can convert the electromagnetic radio wave into a light signal, which can be picked up by a photo sensor, and converted into a soundwave. I have actually built my own version using an LED flashlight. I will put a how-to on this site in a few weeks. Sadly, I did bad on my last test, and my fiancee forbid me from making it until My test blocks are over.

Now what does this all have to do with the above link? Not a lot, but I think it is interesting. Now before I get a lot of emails telling me that an AM radio signal does not behave this way, I will say that it is a little different. It is at a constant frequency, and it varies the amplitude, which encodes the signal. I am not going to get into all that, because frankly, I don’t remember all the details.

I do know this. If you have a large power source, it gives off electromagnetic radiation. I used to coop for NASA at Johnson Space Center in Houston, Tx, and I worked on the vomit comet. They had an awful noise interference problem in the back of the plane because they did not use shielded power wires for the lights.

So as far as this little radio project. If you have an AM signal, and you have a coil of wires, and a very sensitive pizoelectric crystal headset, then you can convert that emag signal into a current, and can listen to it on your headset. So a very easy AM radio can be made, and here is a how-to project telling you how to make it. I will make my own possibly one day, and show you more on how to do it.

[scitoys]

1-watt amplifier

Greg Lipscomb — Wed, 02 Nov 2005 19:55:02 +0000

There is a lot of need in electronic projects for a good amplifier. Here is a small 1 watt amplifier made with simple resistors and transistors. I try to remember back to my electrical engineering days of how to do this, but can’t remember. This is a good website that tells how to use a voltage divider connected to a transistor to amplify a signal. I am thinking of one day making an altoid can pocket amplifier. This is enough for now though. It is important to understand simple circuitry before delving in to more complex circuits. It is easy to get an integrated chip as an amplifier, but all that is really is just a series of daisy-chained transistors.[link]

Transmit radio signal with laser

Greg Lipscomb — Tue, 01 Nov 2005 04:38:54 +0000

This is a how to project on transmitting audio through a laser. I remember some electrical engineering friends of mine doing this same thing. I have always wondered how it was done, but now, I see it is pretty easy. I might have to make my own version of this. Of course, I would not use a laser, cause I don’t have one. I think an LED would do the same trick. It might not have the same sort of distance, but I think I might have to get to work on this.

Link