49 lines
2.8 KiB
Markdown
49 lines
2.8 KiB
Markdown
# picoAM
|
|
A simple but capable AM transmitter for the Raspbery Pi pico!
|
|
|
|
|
|
|
|
## Disclaimer!!
|
|
|
|
The Pi is not able to output enough power to disrupt anything significantly, but with a long enough antenna, will get you in
|
|
trouble and annoy othere. Please use this only for experimental and educational purposes and do NOT use this in a way which might
|
|
cause any disruption!
|
|
|
|
My antenna for this is barely large enough for half of my room to have reception. Please don't go much further than that!
|
|
|
|
**Also**, this project will overclock your pi. However, 200MHz is fine for 99.9% of picos and is SUPER unlikely to damage it unless you
|
|
leave it running for a very long time (days or something in a closed environment).
|
|
|
|
## How it works
|
|
|
|
The Pi generates a 1557kHz PWM signal, which will be the carrier wave. The frequency is not changed, only the pulse width.
|
|
(Sadly, I was not able to make an FM version because FM would require more precise frequency shifts, which the pico just can't do.)
|
|
Then, an audio input is taken in on the right side of the breadboard (blue and green wire), which is clamped and slightly loaded
|
|
so that we don't get nasty interference.
|
|
Then, this clean signal is given to the pico on pin 26. The pico does pulse width changes according to the signal, and outputs the
|
|
AM signal on pin 15.
|
|
|
|
## Circuit Diagram and explanation
|
|
|
|
|
|
|
|
The part which prepares the audio for the pico is not strictly needed, but if you use line inputs, you reeeally should have it.
|
|
It has the following jobs:
|
|
- R2 and R3 try to pull AI- a between the two voltages to be able to record the whole signal in case it is not a grounded one (not needed,
|
|
it can also just be connected to ground. this is basically just extra fanciness with nonzero but very small benefit.)
|
|
- R1 makes sure there isn't too much strain put on the input
|
|
- D1 and D2 clamp the signal to acceptable voltages
|
|
- **An extra resistor of about 50-100 ohms may be added from the AI+ point to the AI- point to load the signal.** This is optional, but
|
|
*can* clean up a little bit of noise if you have long cables.
|
|
|
|
## How to use it
|
|
|
|
- Flash the ino file using the Arduino IDE
|
|
- Cut open an audio cable and take one of the channels and the ground out of the cable's mantle
|
|
- Connect those to jumper wires
|
|
- Take a breadboard and put the pico on there, wire the circuit
|
|
- Add the audio inputs
|
|
- Add a **sufficiently long but not too long** antenna. Mine is about 2m-ish long.
|
|
- Connect the Pi to your PC using the USB port for power
|
|
- Connect the audio input to your PC
|
|
- Tune in to 1557kHz AM
|