Tiny Ladybug Sized FM Spy Bug : 9 Steps (with Pictures)

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.