I have attached the PDF file in the last step to this Inst'able for those without a pro membership.
Step 1: Parts and Prep (Small Stuff)
==These are the small components you will need==
- 555 timer chip
- NPN transistor
- two #103 capacitors (0.01 microfarads or 10,000 picofarads)
- #102 capacitor (0.001 microfarads or 1,000 picofarads)
- some short wires
- two 1 Kilohm resistors
- 10 Kilohm resistor
- 1/8 inch (3.5 millimeter) female audio jack (yours may have more or less than three
wires, but it must have at least two)
- 5 Kilohm potentiometer
==see next step for bigger components==
Step 2: Parts and Prep (Bigger Stuff)
==These are the bigger components you will need==
- 1/8 inch (3.5 millimeter) male audio cable
- AM radio receiver
- Antenna. Yours doesn't have to be made out of a pop can, but the pop can works
(see previous step for the small components)
Step 3: Schematic!!
==Now that we have all of our components ready, lets put this together!==
I suggest constructing this on a breadboard first.
If you don't have a breadboard, you are definitely missing out!
If you have any questions... ASK!
P.S. Don't forget to SUBSCRIBE! : )
Step 4: Testing 1, 2, 3...
==Test your radio!==
To test the AM radio transmitter, simply set the antenna next to your AM radio receiver (Alarm clock) tuned to approximately 600 KHz. Then play with the potentiometer until you can hear your music on your radio. The frequency generated by this devise will be anywhere from 100-480 Kilohertz if you used all the correct component values.
If you hear weird sounds when you turn the potentiometer (and do not hear the audio signal) That means that your radio is working, but your audio signal needs to be configured. try turning the volumed of your audio signal up.
Not working? ASK ME!!! place a comment in the comment section below! : )
Otherwise try these for troubleshooting:
~Is there power applied to your transmitter?
~Is the audio signal on?
~try turning the potentiometer.
~try turning up the audio signal
My antenna, power supply, and audio cable aren't connected to the circuit in the photo above.
Step 5: How... WHY?!?
==So how does this work??==
The audio signal is controlling when the radio signal is being transmitted using its amplitude. this is called amplitude modulation (hence A.M. Radio) (See picture above).
However, as kr.baker pointed out in the comments,
"The audio is "modulating" the RESET pin on the 7555. This means that the signal is turning the carrier completely on or off, as opposed to linear amplitude modulation. Consequently, the audio will be distorted."
He raises a very good point that I hadn't given much or any thought to. You aren't modulating signals like they normally would be modulated. The audio quality will be greatly distorted because of this lack of having "linear amplitude modulation" - kr.baker
for more on the subject of amplitude modulation, go HERE
==YOU AREN'T TRANSMITTING AM RADIO FREQUENCIES!!==
You are transmitting at a low frequency that can be heard at higher AM frequencies. Lets say I transmit music at a base frequency of 300 Kilohertz (KHz) This music can be heard at the frequencies of 300 KHz, 600 KHz, 900 KHz, 1200 KHz,... (etc.) This is called harmonics.
When the radio receiver's picks up a 300 KHz signal on a 2400 KHz band, the signal is heard only faintly. If you were to pick the very same 300 KHz signal on the 600KHz band, it would be exponentially stronger. This is why harmonics are only useful to a degree.
for more on the subject of harmonics, go HERE I HIGHLY recommend this wikipedia page.
==for some more radio information, see the next step!==
this picture shows amplitude modulation. image from http://www.ofcom.org.uk
Step 6: Improving your radio!
I want you to modify your radio and post a comment below that tells us what you did and how it worked! it's that simple!
Although, I do have some suggestions:
- Try changing R2 to a 3.3Kohm resistor.
- Try cutting C3 out of your circuit.
- try connecting the radio antenna to ground through a 1Kohm resistor
Step 7: Extra Info.
The radio transmitter we made can only transmit at frequencies from 110KHz to 480KHz. The AM radio band is from 520KHz to 1610KHz. Harmonics are essential to be able to hear audio signals transmitted from our radio transmitter.
==I buy almost all of my electronic components at MOUSER.com==
==If you liked this, SUBSCRIBE!==
==I'm making more instrucables just like this one!==
I sincerely hope you don't hurt yourself while making this project! That being said, you are solely responsible for everything that happens while constructing this project. If you believe that you are not responsible for your own actions, then god help you. : )