I'd like to share a tiny radio transmitter I made from an Arduino Uno board. If you haven't heard of them, the Uno is a cheap, easy to use microcontroller board. It's essentially a tiny, very low memory computer that can be programmed to perform basic digital and analog electrical tasks. 

These boards are used widely as educational tools and in DIY settings. The first "project" people do with these is usually to make an LED blink. This would require a clever circuit if you were building it from basic components, but with this device you can do the job with three lines of code. Of course, it's more useful for more complicated tasks, like controlling sensors (back when I first got this board I used it to make a crude magnetometer (a device that measures magnetic fields) for example).
![unoradio1.jpg](https://steemitimages.com/DQmV8DBAzHYpVe5AJV6Ec8fumNSyB3s1DkW7rEJM6spsAKs/unoradio1.jpg)

I haven't used mine in awhile, but I had the idea to try and transmit on the AM radio band using one so I brought it out of storage to try out. 

## Transmissions are Oscillations!

*Any electrical oscillation produces electromagnetic waves.*

These waves might be very low power, and they might not be detectable, but they are always there. A calculator with a 20 MHz processor is radiating tiny amounts of 20 MHz electromagnetic radiation (unless blocked by shields), but the amount produced is likely undetectable. You need a properly built antenna to actually get large/usable amounts of radio waves out into the environment. 

This means that a circuit that fires an electrical signal back and forth one million times a second can be converted into a crude jammer/transmitter by attaching a long wire to the oscillator. It will then radiate 1 MHz radio waves that be picked up on radios, wirelessly. The wire is likely a very poor antenna, but it's magnitudes better than having no antenna at all.

In this post I'll be demonstrating using a wire and an Arduino Uno to produce radio waves.

## Uno Radio Waves

The Uno is a moderately sized blue board containing the ATMEGA-328 microcontroller. This chip is a large IC that can be programmed to perform some function. In a way, the Uno is just a big supporting board for this single microcontroller.

![unoradio2.jpg](https://steemitimages.com/DQmYAmLqiJj7Go8QfW5hMPe1pPAyzUe3xju8ofDmtgdJNBZ/unoradio2.jpg)
*ATMEGA-328*

The board itself provides an easy way to program and use this IC: a USB port, easy to access pins, LEDs, and more. Notably, there is a piezoelectric crystal oscillator onboard. This device oscillates at a very specific frequency, and controls the speed of the controller. In the case of the Uno, the microcontroller runs at 16 MHz (compare to the GHz+ frequencies of ordinary laptops...). 

16 MHz means that the device can run one command every 1/16 of a microsecond. I used this as the basis for generating a radio signal. 

The AM-band stretches from about 500 kHz (0.5 MHz) up to almost 2 MHz. I decided to go for the center of the band at 1 MHz to be sure my handheld radio could pick up the signal.

I wrote a simple program that is loaded onto the Uno to generate radio waves. The program tells the device to transmit the letter "V" in Morse code (this corresponds to dot-dot-dot-dash (...-)). Here's how it works (see the end of the post for the actual code if you want to use it yourself):

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The electromagnetic wave is produced by outputting a *square wave* to one of the digital output pins. Digital pins can only output two voltages: High (+5 Volts) or Low (Zero volts). So, to get a 1 MHz square wave that can be heard on the radio, we need to switch the digital pin on and off one million times a second (once per microsecond). However, the Uno time delay commands only go down to one microsecond. If we use a microsecond delay between turning the pin on and off, the output frequency will only be 500 kHz (half a MHz). 

To get around this I used the fact that we know the Uno operates at 16 MHz. Instead of using a time delay comand, after telling the Uno to turn digital pin #8 on I ran 8 useless addition commands (literally just adding 1 to a number over and over). These commands consume 8 microseconds of time, since the processor can do one command per 1/16 of a microsecond. Then, pin #8 is turned off, and another 8 subtractions are calculated (subtracting 1 from a number 8 times). Then the pin gets turned on and again the cycle continues, with a frequency of ... 1 MHz. 

![unoradio3.jpg](https://steemitimages.com/DQmQa7nDGq9Y6mC1hHL8bDVMujPYtjw1PA4M9CYRfo5xpK8/unoradio3.jpg)
*Setup for this silly transmitter. The green wire acts as a crude antenna, while the 9V battery connector connecs to digital output pin #8 on the Uno, which is being used as the transmitter output. I used the battery connector because I lost all of my breadboard wires. The image distortion is due to the fact that I took a panorama to get the entire device in one shot.*

To get the morse code transmission, I just ran the transmitter commands through a few loops to send out DOT-DOT-DOT-DASH (which is V in Morse Code). 

With the wire attached, you can clearly hear the morse code signal on my AM radio (shown as the grey box in the image) from up to a meter away - right around 1 MHz on the receiver as predicted! Since 1 MHz EM waves have a very long wavelength, a longer antenna would likely improve the signal and increase the range. You could even pick up these signals with a car radio if the transmitter was close enough.

![](https://steemitimages.com/DQmPYQa8VgJtGcFCqe2XTLiyXxbwDcwbvFsbUVcjJBfBkk2/image.png)
*This is a square wave, and it's what the transmit pin of this demonstration outputs. The vertical axis represents Voltage and the horizontal axis represents time, so this is just a picture of a switch turning on and off over and over again.*
*[Credit](https://commons.wikimedia.org/wiki/File:Square_wave.svg)*

However, you wouldn't want to use this kind of transmitter to actually send information. Coming from something called Fourier's Theorem, every wave you can make with electronics is actually made up of a sum of sine/cosine functions moving at different frequencies. The result for us is that if you put a 1 MHz square wave (which is all turning a pin on and off is) through an antenna, you won't just transmit on 1 MHz: You'll also transmit on a bunch of other frequencies, at varying signal strengths. So, using this kind of transmitter without first filtering the output to be a pure sine wave will result in you littering the radio spectrum with tons of noise on many frequencies and possibly messing with channels you didn't even know you were transmitting on. 

But even with the noisy output, I think it's a cool demo. Uno's are really cheap (I think you can get off-brand ones for around $5), so you could build one of these and try it out on your radio in about a minute.

## Code

Here's the code, if anyone's interested in trying this themselves. I did my best to comment it well so that you can follow along, but I'm not a very good programmer so don't expect the program to be amazing. Anything behind // is a comment.

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// Super simple 1 MHz AM-band blank radio wave transmitter for Arduino Uno

void setup() {
  // Initialize transmission pin
  pinMode(8,OUTPUT); // Use Digital Pin 8 for transmission. Change to whatever pin you like.
}

void transmit_1MHz() { // Transmitter Function - Custom Function
  // Run transmitter
   int j = 1; // Dummy Variable for timing
  
  digitalWrite(8,HIGH); // Turns on Digital Pin 8

  // Run 8X dummy commands to delay 1/2 microsecond (at 16 MHz clock speed)
  j++;
  j++;
  j++;
  j++;
  j++;
  j++;
  j++;
  j++;



  digitalWrite(8,LOW); // Turns off Digital Pin 8

  // Run 8x more dummy commands
  j--;
  j--;
  j--;
  j--;
  j--;
  j--;
  j--;
  j--;

  // The result is a 1 MHz square wave: The voltage is high (+5V) for 1/2 a microsecond, then low (0V) for 1/2 a microsecond. 
}


void loop() { 
  
  // This runs the transmitter on repeat
  // To help with identifying the transmission: Transmit the morse code for the letter "V": ...-

  for (int i = 1; i <= 4000; i++) { // Run for 400 milliseconds, since each transmit run takes 1 microsecond DOT
    transmit_1MHz(); // Turn on transmitter - each run takes 1 microsecond
  }
  delay(200);

  for (int i = 1; i <= 4000; i++) { // Run for 400 milliseconds, since each transmit run takes 1 microsecond DOT
    transmit_1MHz(); // Turn on transmitter - each run takes 1 microsecond
  }
  delay(200);

  for (int i = 1; i <= 4000; i++) { // Run for 400 milliseconds, since each transmit run takes 1 microsecond DOT
    transmit_1MHz(); // Turn on transmitter - each run takes 1 microsecond
  }
  delay(200);

  for (int i = 1; i <= 20000; i++) { // Run for 2000 milliseconds, since each transmit run takes 1 microsecond DASH
    transmit_1MHz(); // Turn on transmitter - each run takes 1 microsecond
  }

  delay(500);
  
}

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## Conclusion

I can already think of some ways to improve this (adding a filter, adding voice, or using the square wave output to drive a higher frequency transmitter), and I may try that in the future. Really this is just a quick demonstration that you can indeed broadcast weak radio signals with these common boards. 

Let me know if you have questons or comments, or if I made any errors. 

*Thanks for reading!*

________________
*All images not credited are my own. You are welcome to use them with credit.*

*[Read more about the ATMEGA-328 here](https://en.wikipedia.org/wiki/ATmega328)*