The Ultimate FM Transmitter (Long Range Spybug)
By ASCAS on July 13, 2014
Introduction
Hello There! I'm Angelo. I'm 15 and I love to build projects during my pastime! I plan to become an engineer someday and work for a company that innovates new products. My #1 inspiration is my grandpa! He was a great engineer and the best grandfather a geek could ever have. He used to pick me up from school, and we would shop at hardware stores before heading home to build projects together. After he passed away, I continued my hobby in his honor. Most of my projects focus on Electronics, Woodworking, and Robotics. I've been making projects for a while and have gained a lot of knowledge through my experience. I now compete in the annual "National Robotics Competition" and earned last year's championship title. I will be one of our country's representatives in this year's International Robotics Olympiad in Beijing.
Have you ever wanted to broadcast your own radio station within the neighborhood? Ever get curious about where people get those "Surveillance Bugs" from spy and action movies? This small and simple FM transmitter is the toy that geeks have always wanted.
FM transmitters can be complicated to build, but this tutorial teaches you how to make a foolproof FM transmitter. It includes the PCB layout and schematics. It has a range of up to 1/4 mile or more and is great for room monitoring, baby listening, and nature research.
It's been a while since I last posted a project. I apologize for the late replies, especially for the projects I promised to post. I've been busy with TV interviews lately. I'm back now with a hoard of unpublished guides!
Please Watch: Celebrating the 1st episode of my new YouTube channel! It's my first time documenting a project with videography. I hope you enjoy the video! Please leave a comment below; I would appreciate some advice regarding the video.
Disclaimer: This project is for educational purposes only and is not intended to interfere with present radio channels. Neither the site nor I am liable for careless actions. Please check the legality before attempting the project in your area.
Technical Specifications:
- 1/4 Mile Radius Range
- Powered By A 9V Battery
- Lasts For Several Days
- Adjustable 87-108MHz
[Image: Two images of the assembled FM transmitter circuit powered by a 9V battery.]
Step 1: Gather The Parts
All of these parts are available at any branch of RadioShack!
Miscellaneous:
- Copper Clad PCB/Perfboard
- Solid Gauge #18 Wire
- Electret Microphone
- 1/4 inch Bolt
Transistors:
- 2N3904 General NPN Transistor (2x)
Capacitors:
- 15pF or 40pF Trimmer Capacitor
- 100nF Ceramic Capacitor (2x)
- 10nF Ceramic Capacitor
- 4pF Ceramic Capacitor
Resistors:
- 1M Ohm 1/4W Resistor
- 100K Ohm 1/4W Resistor
- 10K Ohm 1/4W Resistor (3x)
- 1K Ohm 1/4W Resistor
- 100 Ohm 1/4W Resistor
Tools:
- Pliers
- Soldering Iron
- Hot Glue Gun
[Image: An image displaying various electronic components including resistors, capacitors, transistors, a microphone, a bolt, and wire, alongside tools such as pliers, a soldering iron, a multimeter, and a voltage detector.]
Step 2: PCB & Schematics
I designed a compact PCB layout for Art Swan's miniature FM transmitter circuit using Fritzing. Use this step as your reference for the assembly.
About The Circuit: This is the exact description from Art Swan, the circuit's Author: "This miniature transmitter is easy to construct and can be picked up on any standard FM receiver. It has a range of up to 1/4 mile or more. It's great for room monitoring, baby listening, and nature research."
Download Link: PCB Layout and Schematic
[Image: A Fritzing software view of the PCB layout and a circuit schematic diagram.]
Step 3: Print The PCB Layout
Download the PDF file then print it with your printer's standard settings.
Download Link: PCB Layout PDF
[Image: An image showing a printer outputting a PCB layout. Another image depicts cutting the printed layout with a ruler and craft knife.]
Step 4: Develop The PCB
I'm using something called presensitized PCB fabrication, which is different from the toner transfer method. If you're not familiar with presensitized PCBs, it's better to go with the toner transfer method.
Presensitized PCBs: I expose mine directly to a 10W fluorescent lamp for 5:20 minutes then use a dilute solution of Sodium Hydroxide to develop the exposed PCB.
Here's a separate tutorial for the PCB fabrication: The text describes PCB fabrication as a basic skill for various engineering disciplines, achievable in 10 minutes, using a high-quality photosensitive agent. (Original text in Chinese).
[Image: An image of a PCB being exposed to a fluorescent lamp, a kitchen timer displaying '00:03', a PCB being developed in a blue tray with a chemical solution, and a bottle labeled 'Sodium Hydroxide'.]
Step 5: Etch The PCB
Pour Ferric Chloride onto a plastic tray then start to etch the PCB.
[Image: An image of a PCB being immersed in Ferric Chloride for etching in a blue tray.]
Step 6: Clean The PCB
Use a swab and Acetone to remove the photo-positive layer/toner.
[Image: An image shows cleaning the PCB with a swab and Acetone.]
Step 7: Solder The Components
Use Step #2 as your reference. Solder the smaller parts first. Start with the resistors, capacitors, transistors, coil, antenna, and then the 9V battery clip.
[Image: Several images illustrate the process of soldering components onto the PCB, including close-ups of soldered parts and a tray containing various components.]
Step 8: Construct The Coil
Strip a solid gauge #18 wire. Use a 1/4 inch bolt and turn the wire 7-8 times.
[Image: Images demonstrate winding a coil around a bolt using pliers.]
Step 9: Adding The Antenna
Solder a hook-up wire to the antenna pin, which is located on the 2nd transistor's collector pin. Use a maximum of 8 inches and a minimum of 5 inches.
[Image: Images showing soldering an antenna wire to the PCB.]
Step 10: Recycle A Battery Clip
The key to this compact transmitter is the ingenious battery clip. You can get one by dismantling a scrap 9V battery.
[Image: Images showing dismantling a 9V battery to extract the battery clip.]
Step 11: Glue Them Together
Apply a generous blob of hot glue to hold the clip and the transmitter circuit together.
[Image: Images show applying hot glue to secure the battery clip to the transmitter circuit.]
Step 12: Tune The Transmitter
Turn on your radio then tune it to your desired channel frequency. You'll get more range from vacant channels. Do not touch the coil; just turn the trimmer capacitor until you hear feedback from the radio.
[Image: An image shows the completed transmitter connected to a radio for tuning.]
Step 13: Don't Forget To Leave A Comment [Stay Tuned]
I've always dreamed of starting a continuous DIY video channel. I hope this goes out well. Please leave a comment below. Thank you!
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