Introduction: Spy Aduio
This is a spy device that is really small and can be hidden any were it is a transmitter and your mobile is the reciver. This is a very small radio transmitter and can transmitt aduio signals up to a radius of 100 m.
For recording I recommend you to use an android phone as it has a wide band range .
They transmit on the FM band in the range 88MHz to 108MHz. It can be adjusted to transmit above or below the band and you need a radio that will pick up these frequencies, to detect them.
Since the FM band is almost entirely filled with radio stations, we will be providing details on how to adjust a radio so it will scan EITHER above the band or below the band. Most radios can only be adjusted 10MHz above or below but this will be enough to provide a "blank" space for your transmitter.
FM transmission provides perfect quality and when one of these transmitters is used in a house and received on a good quality radio, you cannot tell if the person is actually talking in the next room or via an FM link, through a radio.
If you think of this project is cool vote for me in the contest.
Step 1: Parts
4)Capacitor 4p7, 22n
For the coil use a 24 gauge coil and wind it over a thin pen.
Additional parts required to build a field strength detector to test if the bug is working.
Step 2: Final Step
Use a heatsink to enclose the circuit mount this on a 9v battery clip. Tune over the radio till u get an aduio output on your mobile. For best result use android phones. This circuit provides a clear audio output before testing it on a android use a high signal radio to find the perfect band tune the presets to get a required band as almost the entire fm band is filed with stations. For the antenna use a small 5cm copper wire . This whole circuit cane also be soldered board less on to a 9v battery clip. But use the heat sink to keep the circuit in one piece . If you don't get a signal check for the connections try changing the coil .
Step 3: Field Strength Meter
After making a transmitter, you will want to know if it is transmitting. In the case above, the circuit will only produce a carrier and this will be heard on the radio as a "quiet spot."
Rather than chasing up and down the dial, I made a piece of test equipment to let you know the bug is transmitting and the approx frequency of transmission.
It is called FIELD STRENGTH METER MkII.
The photo below shows the Field Strength Meter near the bug. The plastic knob on the trimmer allows adjustment without affecting the detecting circuit. Simply turn the knob (with the two antennas near each other) and the 3 LEDs on the project will illuminate.
Visit my instructable to get details on how to build a field strength meter.