In this Instructable we will cover:
- The Schematic and some basics of how it works
- Parts needed
- Getting the PCB layout onto a prototyping board (pegboard)
- Laying out the components on the board
- Tools needed to assemble the kit
- Soldering everything together.
Below is the schematic from our friends at Upverter.com.
Step 2: Parts List
- 1x 22 k Ohm Resistor $0.07
- 1x 330 Ohm Resistor $0.06
- 1x 1000 pF Ceramic Capacitor $0.06
- 1x Omnidirectional Microphone $1.29
- 1x 1.0 uF Aluminum Electrolytic Capacitor $0.32
- 350mm (1 foot) of 20/22 AWG Sold copper or Magnetic Wire
- 1x BC547 Bipolar NPN Transistor $0.07
- 1x Coin Cell Battery Holder $0.60
- 1x .022uF Ceramic Disc Capacitor $0.16
- 1x 47 K Ohm Resistor $0.06
- 1x 10 pF Ceramic Capacitor $0.08
- 1x SPST Slide Switch $0.37
- 1x Variable Capacitor 9.8 pF to 50 pF $0.48
- 1x Dual mini breadboard $2.19
- Altoids Smalls Tin
- CR2032 Cell Battery
Step 3: Pegboard Layout
- PCBs for the layout won't be available for some time so users need to be able to make this themselves on a Peg board
- Becuase a Pegboard layout is needed the traces had to be routed on a single side.
- The whole project is going to be mounted in an Altoids Tin to conceal it
If your going the Peg board route then print the PDF file out and cut it to size. Overlay it onto the Peg Board and hold it up to the light to get the component holes lined up with the Peg Board's grid. Then tape the layout in place. Be sure the copper grid is on the bottom of the peg board and the layout is taped to the top. Go ahead and take a pointed object like the lead from one of the parts and poke out all the component holes.
Step 4: Tools
- Soldering iron
- Needle nose pliers
- Wire cutters
- Wire strippers
- Helping hand/PCB clamp
- Small flat head screwdriver or Probe
- Solder braid/pump/bulb
- Magnifying glass
- Electrical Tape
- Small Phillips Head Screwdriver
- FM Radio
Now to start putting everything together.
Step 5: Sizing the Pegboard
I used a ruler to line up where i wanted to score the board. Then i took a box cutter and Scored along the edge of the ruler a couple of times. Then i took my pliers and snapped the edge off. Use a file or 100 grit sand paper to clean up the edges. Then drop it into the tin to see how it fits.
Step 6: Placing the Resistors
With the resistors in place, bend the leads out so they will not fall out when you turn the board over to solder them into place. When working with pegboard like this i like to use the leads of the components to link the traces from one component to another. So bending you leads in the direction of the nearest component they will be linked to is a good idea.
With the resistors in place flip the board over and solder them in place. Don't worry about soldering the ends of the leads down as traces until we get all the components in place. But go ahead and use your pliers to bend them around to where they need to go and cut off any access so its out of the way.
Step 7: Placing the Capacitors
As for the Ceramic capacitors make sure you have the correct ones going into the correct spots. The Capacitors will be labeled on there bags but not on the components themselves. So double check the capacitor and where it goes on the board.
- C2 - 1000 pF
- C3 - 10 pF
- C4 - .022 uF
- C5- Variable Capacitor
Like before bend the lead out a bit in the direction they need to go. Flip the board over and solder the leads into place. Then route the leads and trim as needed.
Step 8: Transistor and Mic
Make sure you have the transistor lined up correctly. As you can see in the reference image the flat side of the transistor needs to be facing to the right. This puts the Emitter on the bottom, Base in the middle and Collector on the top. Bend the leads out a bit and move on to the next component.
Feel free to leave the switch off if you want. It will make fitting it into the Atoids Smalls tin a bit easier. I've left off the switch here so we'll need to bridge the solder trace area where the switch would be. If you decide to use the switch it will need it's leads bent in ever so slightly so they will fit into the board. The leads of the switch won't be long enough to bend towards other components. But friction will hold it in place while you solder it.
The mic will drop into place without any issue. Bend the leads as needed and your ready to solder everything in place.
Step 9: Making Your Inductor and Antenna
Now take a 50mm piece of the wire and solder one end of it to the 1st turn on L1 near the top of the board. This will be your transmitter's antenna. If you are using magnetic wire then be sure to scrape the coating off the end of the Antenna wire and the turn you'll be soldering it to before soldering it in place. If you are using regular wire then strip the end. Wrap the end into a little hook so you can hook it around the first turn and solder it into place.
Step 10: Battery Clip
Now take the battery clip itself and place it on the board so the battery can be inserted into the right hand side of the board. Notice the 2 tabs in the back of the clip. The need to be towards the middle of the board. When placing the clip it will be a tight fit between it and the coil. Solder the clip in place and we are ready to make the traces.
Step 11: Soldering the Traces
Take your time and do one trace at a time. Like they always say "measure twice and cut once". In this case check and verify the trace placement twice and solder once.
Step 12: Wrapping It Up
If you decided to use the switch you will need to measure out where the switch will stick out so you can cut an opening for it in the tin. A 1/4 inch drill bit should be sufficient for making a large enough hole for the switch. For best reception you will want the antenna to be on the outside of the tin so feel free to drill a small hole to allow the antenna to stick out.
We only want the board to sit in the Altoids tin. It shouldn't be permanently mounted since you will have to remove the board in order to change the battery. Of course the board could have been made smaller but then it would be difficult to put together as a kit.
So there you have it a nice little FM Listening Bug you can use to spy on your friends. Pair this with my Electronic Bug Detector Kit and you have a fun little electronic hide and seek game. Create multiple bugs and hide them all over the place. Or you can just use the bug as an FM wireless mic and have fun playing Radio DJ.
NOTE: To date i haven't been able to get this design to actually transmit to an FM radio. I found the original Schematic at this web site and assumed it was a functioning design. I used the More Stable design for this project. Maybe the BC547 transistor needs to be replaced with either a 2N3904 or a 2N2222. The Coil may also be too big as well, but i don't have the available time to troubleshoot the project any further.
UPDATE (10/5/2012): I found a problem in the board layout. The transistor is pictured on the layout backwards. I'll be working on a new prototype soon and make sure everything actually works before updating the instructable. I'll keep you all posted.