This instructable will tell you how to operate Niftymitter 0.24, a small open source FM transmitter. More information on the design can be found at www.openthing.org/products/niftymitter.

This transmitter is in development and has not yet been approved by any regulators. It is a low power transmitter and works over a very short range - please ensure that by using it you are not interfering with any other nearby transmitters.

Step 1: Plug in a Source

Plug in any audio source into the 3.5mm jack socket. Set the volume on your source as low as possible.

Step 2: Switch On

Switch the transmitter on.

Step 3: Tune In

Make sure your transmitter and radio receiver are at least 2m apart to avoid tuning in to a harmonic frequency. Switch on your radio and tune the radio in to the transmitter. This should be broadcasting on a frequency between 88 and 91 MHz FM, transmitting silence.

It is difficult to be accurate here as: a) the frequency can very depending on atmospheric conditions and b) the scale on your radio might be calibrated differently to the scale on my radio, so would give a different reading of what frequency it is receiving on.

If you are having difficulty tuning in, you may need to retune the transmitter, which is described in step 5.

Step 4: Turn It Up!

Carefully turn up the volume on your audio source to a comfortable level. If you turn up too loud, the signal will sound distorted (it really doesn't need to to be very loud).

Step 5: To Retune Niftymitter

Slide out the circuit box.

Use a small 3mm slot headed screwdriver to adjust the 'trimcap'. It is best to use a screw driver with an insulated handle to minimise interference with the transmitting frequency, or ideally a trimtool such as this one from Rapid.
The trimcap is a small brass coloured component accessed by the hole marked 'tuning'. Clockwise for up, andticlockwise for down, it only requires very fine adjustment.

Step 6: To Replace the Battery

Slide out the battery tray. Unclip the battery from the PP3 clip, recycle/recharge and replace.