From 5996134f2ebc7bfda5257495a96dbd778a49b93a Mon Sep 17 00:00:00 2001 From: Daniel H Date: Sun, 30 Apr 2023 14:13:02 +0200 Subject: [PATCH] Update README.md --- README.md | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/README.md b/README.md index 2610d24..9eb75f6 100644 --- a/README.md +++ b/README.md @@ -1,2 +1,45 @@ # picoAM A simple but capable AM transmitter for the Raspbery Pi pico! + +![Image of assembled circuit](https://media.discordapp.net/attachments/1077080199847489626/1102196399577247774/20230430_133433.jpg) + +## 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 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! + +## 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 + +![Image of circuit diagram](https://media.discordapp.net/attachments/1077080199847489626/1102203487363792956/SmartSelect_20230430_140248_Flexcil.jpg) + +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