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I wanted to know how small a FM spy bug could be build when manually assembled.

This is what I came up with, it measures about 0.05 square inches and is powered by a single 1.55V silver oxide battery.

Frankly, this is just a fun object, I don`t have a practical use for it.

I`m sure professionnally made spy bugs could even be smaller and work at higher frequencies which allows the antenna to be made smaller.

Step 1: Specifications

Watch the video to see the spy bug in action!

https://www.youtube.com/watch?v=_Na0Ac7FTbk

FREE: You will also find a link in the video description to download the complete PDF manual and Gerber files (needed for PCB manufacturing).


Power supply:

1.55V silver oxide button cell or any other voltage source from 1.1V to 1.55V

Current consumption:

less than 200uA

Operating time:

at least 48h with the smallest currently commercialized battery

Range:

Depends on the antenna, with a quarter wave length antenna about 160ft

Best suited for indoor room to room surveillance

Frequency:

FM Radio frequencies, tested at about 85MHz

Step 2: The Circuit

All the components here are the smallest that could be obtained for a reasonable price. All the components together cost about $6 US.

To the left we see a microphone which works down to a voltage of 0.9V. Its maximum voltage is 1.45V though, which is why we need to decrease the battery voltage a bit. This is done with the schottky diode.

The oscillator to the right is then modulated with the microphone output signal.

The frequency can be adjusted with C4 and/or L1. Once everything is assembled it`s easier to replace L1 or put a capacitor in parallel with it. If you watched the video on the previous page you will understand why. :-)

Step 3: The PCB

The PCB has to made with a layout editor. One can use a software like EAGLE for that (which is free for personal use) or any of the other many software solutions on the market. Some examples are Altium Designer, OrCad, Cadence etc.

The PCB could possibly be made at home but I didn`t have the courage/patience/money to try it out. This PCB was made using a pooling service in the US for a very low price.

Step 4: Solder Paste

First we grind off some of the material from the borders.

Then we need to deposit some solder paste on each pad. Solder paste is a powder metal solder suspended in flux.

To deposit the paste on to the pads we will need a microscope (otherwise we couldn`t distinguish the pads). The solder paste could be put into a syringe with a very small diameter needle or we just use a needle for that. I found it to be easier to use the needle.

The right amount of paste on each pad is important, if there is too much it should be removed before proceeding.

Step 5: The Components

Now the components are put on the board with the help of fine tweezers.

Step 6: Soldering

The board now needs to be heated. This can be done in an oven or on a hotplate. I found it easiest to glue the board on to a hotplate with superglue before depositing the solder paste and the components.

When assembled the hotplate can then just be turned on without moving the PCB, lowering the risk of accidently shifting the components.

The temperature is adjusted to about 250C (480F). As soon as the solder paste melts it will connect all the components to the PCB traces just like normal solder wire. The board should then be removed (careful not to shake it too much) and left to cool down.

Step 7: Battery

With the layout I used we could then solder a wire into two vias on the back that serves as a battery holder.

Alternatively two wires can be connected to + and - in order to connect a different type of battery.

Step 8: Antenna

The last step is to connect the antenna wire. Ideally it should be at least 1/4 wavelength long.

The wavelength is calculated like this:

Wavelength = speed of light / frequency. That means for about 100MHz we would get 75cm (about 2.5ft).

I agree this is pretty long, but the wire can be very thin which can make it hardly visible.

Have fun! :-)

Step 9:

<p>Coming soon: 916MHz, 400m range bug in a ballpoint pen.</p><p>https://www.facebook.com/Tom-Tech-1162318370524245/</p>
<p>You don't know how sad I am seeing and hearing foreigners use the US standard measuring system. :-( It makes me sooooooo sad. :-((</p><p>It's a stupid system that practically no one uses unless they're selling to Americans. </p><p>Carry on........</p>
<p>There are two kinds of people in the world, people who use the metric system and people who who been to the Moon.......and back......several times.</p>
<p>Do you know that NASA itself uses the metric system ? CQFD</p>
The German scientists behind the Apollo missions would have use the metric system
<p>I agree. Imperial System, my foot. The metric system is a LOT better seeing as it doesn't have confused measurements like 12 inch in foot, 3 foot in yard, 1760 yards in a mile... Why would America take normal lengths and make them complicated?! That's like saying 2 + 2 = 3 + 1 + 4 - 2 - 2 = 4. Honestly though, I have just one way to explain. Americans *rolls eyes*</p>
<p>The metre is defined as the distance traveled by light in a specific fraction (1299 792 458) of a second. I want to teach this to my children.<br><br>Because science!<br></p>
<p>You are being crass and narrow-minded. The Imperial system isn't American, it comes from the UK and is centuries old - the USA is only a few hundred years old. The metric system has some advantages and is used in science and technology. I was in research for 40 years and never used anything else. But the Imperial system isn't some haphazard accident: it's a perfectly natural and obvious system which takes account of everyday observations: a man's foot is a convenient measure; a thumb-joint is similar. We then say let there be twelve thumb-joints in a foot and call it one inch. And so on and so on. And base 10 is only special if you happen to like it: base 12 has much going for it, being divisible by 2,3,4, and 6. Before you dismiss something as bollocks, perhaps you should be more aware of its place in History.</p>
<p>Haha, where I live now we use both. It's weird but I got used to it.</p>
<p>This must be the smalles device on instructables I've ever seen. It would be great if you could add the assembly diagramm to know which part goes where.</p><p>Thumbs up for this beautiful piece of engeneering! </p>
<p>Thanks. When re-doing the layout it would be wise to place C4 just below L1 on the outer edge. Will make it easier to adjust.</p>
<p>Lol C4 the explosive? Nah jk</p>
there is a mistake in circuit diagram C4 and L1 got to be conected in paralel between +b and colector of Q1, circuit board tells that.<br>I gonna give a try soon, seem nice.<br>Thanks
<p>Hi, they are connected in parallel between collector of Q1 and VCC. It's just the way I drew it that may be confusing.</p>
<p>I am sorry, you are right, I was confused thinking they are conected to B. Is a nice circuit by the way!!</p>
<p>&quot; view all steps &quot; in non-functional &quot; on this instructional.</p><p>GREAT instructional, however.</p>
<p>CANCELL &quot; View All Steps&quot; problem. My cookies were not turned on. My Deepest Apology.</p>
<p>This is some great stuff! I am really impressed with the potentials of RF technologies as more as I discover them.</p>
<p>Watched the video. Didn't read anything. Good job! </p>
<p>excellent. :)</p>
<p>Very nice,</p><p>Love the ghetto battery holder ;)</p>
Thanks! :-)
Great job, thanks for sharing.
Do you sell a kit for these??
Hi, no I don't. All the parts are readily available on Digikey.com (or any of their other country specific websites). If you live in North America the whole project will cost you not more than $20 provided you have the right tools. The only thing I can provide is the board layout (gerber files) which can be uploaded to Oshpark.com for example or any other PCB manufacturer. The link for that is in the Youtube video description.

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