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

Step 1: What you need

• Complete Parts List [.xls]
• PCB Layout v0.24 [.png]
  
  • The PCB source is designed for etching onto copperplate, using iron on acetate (such as that described here) or using Michael Shorter's laser engraving method described here [instructables].
    
• Circuit assembly diagram for etched PCB [.png]
  
  You will also need the following tools:
  Soldering iron, kit and solder.
  Wire snips.

Comments

[sciencetor2]

are solder lines on an all purpose radioshack pcb not an option here as an alternative to etching?

[royshearer]

I'm not familiar with that - tell me more!

[sciencetor2]

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?

[jtc10512]

is that pink thing in the center the tuner?

[royshearer]

Yes, it is the trimmer capacitor, tuned with a trim tool or screwdriver.

[alexanderall]

Where does the switch go on the on the pcb?

[burdockwing]

so wait what does this exactly do?

[royshearer]

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.

[technozook]

could you post a scamatic cus i cant etch my own board

[royshearer]

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

[danger man 1]

is it possible to make this work with out a battery?

[royshearer]

I would imagine so, just use a 9v power supply in place of the battery?

[coolacid]

What goes in the Y-ish symbol between the 9V and the GND?

[cliffyd]

its for an antenna wire.

[royshearer]

 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

[______]

The slide show is out

[______]

Yup

[coolacid]

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]

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..

[expert_vision]

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.

[expert_vision]

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]

Oh right, that makes sense.

[______]

Has anybody but me built it and tested range. Range is 1 foot to 250 feet!

[guitarmaster101]

Is there mabye A possible way to make it transmit farther

[t.rohner]

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]

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)?

[t.rohner]

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...)

[hitachi8]

what is the Trimmer Cap ? UF ? 

[Beduk]

I dont know what a trimmer cap is.uf stands for microfarad

[hitachi8]

i know , i was just asking for the capacity .
exemple : 20 UF  

[royshearer]

Apologies, that should be a 4.2- 20pf Trimmer capacitor or similar

[royshearer]

Have updated parts list to 0.24.1 accordingly

[hitachi8]

Thank you , 

[engr.tahir]

 Hello! plz tell me how much area it covers???

[royshearer]

so far seems to be 6m - 20m depending on the environment.

[oc80]

could you use 12 volt instead of 9?

[royshearer]

I've not tried that, but its a sensitive circuit so I doubt it.

[spacetarget]

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.