Instructables

Assembling a Niftymitter v0.24 board - a short range FM transmitter

Picture of Assembling a Niftymitter v0.24 board - a short range FM transmitter
This Instructable will guide you through assembling the circuit for Niftymitter, an open source mini FM transmitter. The circuit uses a free running oscillator and is based on Tetsuo Kogawa's Simplest FM transmitter.

The project is housed at www.openthing.org/products/niftymitter
 
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Step 1: What you need

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niftymitter circuit assembly v0.24.png

Step 2: Solder on the resistors and capacitors

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Place comonents flush up against the board from above. After soldering the legs onto the pads, trim of the excess.
Start by soldering all the resistors. Follow with all the capacitors and the jumper lead. Ensure that the electrolytic capacitor is oriented as described on the circuit layout diagram, the negative side away from the socket.

Step 3: Solder on the socket, coil and trimcap

Picture of Solder on the socket, coil and trimcap
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Next solder on the socket. Take care to ensure the socket is solidly soldered on. Solder on the trimcap, taking care to orient the flat side as shown. Then add the coil. The instructable for making the coils is here.

Step 4: Solder on the transistor

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Finally add the transistor, taking care to orient the pins correctly.

Step 5: Add the power connections

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Solder on the positive lead from the PP3 clip to +9V. Add a short length of wire to the ground connection.

Step 6: Prepare the switch

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Bend the positive lead of the switch LED around one of the switch pole legs as shown. Solder and trim the LED leg as shown. Bend over the remaining LED leg to make a loop.
lseemann10 months ago
nice work. i want to build one. can i replace the 9V battery with USB connector? Would it be enough its 5V 1A to power the device?
are solder lines on an all purpose radioshack pcb not an option here as an alternative to etching?
royshearer (author)  sciencetor21 year ago
I'm not familiar with that - tell me more!
well basically its a prototyping board, its a prepunched pcb grid with each hole having a copper circle around it, and you draw paths with solder rather than making a print of the paths ahead of time, would using solder as thhe conductor be an issue?
jtc105122 years ago
is that pink thing in the center the tuner?
royshearer (author)  jtc105122 years ago
Yes, it is the trimmer capacitor, tuned with a trim tool or screwdriver.
Where does the switch go on the on the pcb?
burdockwing3 years ago
so wait what does this exactly do?
royshearer (author)  burdockwing3 years ago
Niftymitter broadcasts any audio signal that you put into it on FM radio over about a 20m radius so that you can listen in using a FM radio. like an iTrip.
technozook3 years ago
could you post a scamatic cus i cant etch my own board
royshearer (author)  technozook3 years ago
Schematics can be found at Tetsuo's site here:
http://www.translocal.jp/radio/micro/howtosimplestTX.html

Or as a .png here:
http://niftymitter.googlecode.com/files/niftymitter%200.23%20electronics%20schematic.png

Or as a eaglecad .sch (not a very good one at the moment to be honest - please improve) here:
http://niftymitter.googlecode.com/files/0.23.sch
is it possible to make this work with out a battery?
royshearer (author)  danger man 13 years ago
I would imagine so, just use a 9v power supply in place of the battery?
coolacid4 years ago
What goes in the Y-ish symbol between the 9V and the GND?
its for an antenna wire.
royshearer (author)  coolacid4 years ago
 That is a hole to solder on an antenna if you fancy. I don't know much about how one should do that. Will annotate it better in future versions.
check out my new reciving and/or transmitting antenna Ins. soon today
______ ______3 years ago
The slide show is out
Yup
Nice! I made mine and tested it. I really works. It's kind of tricky to tune it, but it's awesome anyhow.
But there's an annoying buzz in the audio. I was wondering if it's something I did or if it's a known issue.
royshearer (author)  coolacid4 years ago
That's great! The tuning is tricky indeed, and definitely needs improving. Buzzing is not a known issue in the units I have made. That kind of thing normally suggests a problem with grounding somewhere in the circuit - check all connections to the negative terminal of the battery are good?
Otherwise I imagine it might be a tuning issue still, or the signal might be distorting if the input level is too loud, in which case you could try turning the volume right down on whatever your source is..
I also experience a buzz in the audio and it persist even if I unplug audio input. As a power source I use a PC PSU's 12V line with a 2.7V zener, so i get 9.3V. May be I should try a 9 V battery or 3V zener or a stabilizer.
The buzz was because of the PC fans .. LOL. Also any PC activity cause small disturbance on the PSU DC voltage lines. So the VCC has to be pretty stable(like a battery).
royshearer (author)  expert_vision3 years ago
Oh right, that makes sense.
______3 years ago
Has anybody but me built it and tested range. Range is 1 foot to 250 feet!
Is there mabye A possible way to make it transmit farther
t.rohner4 years ago
These types of oscillators are very unstable. There are better designs, which are only a little more complicated to build.
If it's your first transmitter, it's ok to play around with. (My first ones were of similar designs. That was at age 12, at age 17 i made my HAM license.)

But i don't think this one is of much practical use.

royshearer (author)  t.rohner3 years ago
Yeah the circuit is very unsophisticated, would love to improve it but do not have the know how. Can you suggest an better open alternative that would also fit into a similarly sized package (approx 27mm by 52mm board)?
On this site you can find different schematics of basic transmitters.

http://www.zen22142.zen.co.uk/Circuits/rf/lrfmtx.htm
or the main rf-page
http://www.zen22142.zen.co.uk/Circuits/rf/rf.html

The first circuit uses a capacitive diode for modulation, where your design uses the the varying capacity of the transistor for modulation. Secondly, there is a amplifying stage, which not only amplifies the rf, but also decouples the oscillator a little bit from the antenna.
But if you want something real stable, you need a crystal-controlled oscillator or a PLL circuit. These designs are much more complicated, but lately you find these small transmitters for feeding your mp3-player sound to your car stereo via FM-radio. So there are definitely some highly integrated circuits to do this in such a small size.(maybe it's easier to buy one of them, but then it's not home-brewed...)
hitachi84 years ago
what is the Trimmer Cap ? UF ? 
Beduk hitachi83 years ago
I dont know what a trimmer cap is.uf stands for microfarad
hitachi8 Beduk3 years ago
i know , i was just asking for the capacity .
exemple : 20 UF  
royshearer (author)  hitachi84 years ago
Apologies, that should be a 4.2- 20pf Trimmer capacitor or similar
royshearer (author)  royshearer4 years ago
Have updated parts list to 0.24.1 accordingly
Thank you , 
engr.tahir4 years ago
 Hello! plz tell me how much area it covers???
royshearer (author)  engr.tahir4 years ago
so far seems to be 6m - 20m depending on the environment.
oc804 years ago
could you use 12 volt instead of 9?
royshearer (author)  oc804 years ago
I've not tried that, but its a sensitive circuit so I doubt it.
spacetarget4 years ago
Good work! I like the simple board layout.  This is a great low parts count transmitter.  Yes, the more parts the more stable, but the whole idea here is simple and eazy. I have made a lot of these. Lots of fun.
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