This AM transmitter is based on one 555 Timer IC and one NPN transistor. Using a condenser mic with 1.5V AA power source for the mic, I can transmit at a short distance to a portable AM radio. The result is a very noisy signal which produces barely audible audio transmission but it works.

I tried to embed a demo video but was unable to, so if you click on link here http://youtu.be/j5-urx1tbXE   you will see a video of my project setup to get  an idea of the quality of audio being transmitted.  I have turned the radio volume all the way up to be able to hear my voice.

CREDIT: This project is based on the AM transmitter by user RTTY21:  http://www.instructables.com/id/Easy-AM-Transmitter

The above project got me interested in the 555 timer IC. I did a project with this nifty little IC which you can see here: http://www.instructables.com/id/555-Swiss-Army-Knife-with-a-pot-photoresistor-an

There are many suggestions out there on how to get a better quality audio such as grounding the circuit to earth and/or a longer antenna. Some readers suggested OpAmps. Personally, I think this is as far as I want to go with this project. It's a cute project but there are other RF projects in my DIY queue waiting for their turn. 

There's no need for me to explain the theory behind this transmitter because it has been done in RTTY21's project page along with man useful readers' comments.  You can refer to my very short video to get a feel of how weak the signal will be without the enhancements other readers have suggested. 

Overall, it's a nice project and that's why I added it to my RF projects To-Do list. It's my first RF project ever and my second transistor project. So I am really excited about it. 

My next project may incorporate an AM radio receiver IC such as the TA7642, or I might go for ATMEL's AM/FM receiver IC the T4258 which is commonly used in car radios. Whatever piques my interest.

I am indebted to the good work of so many folks who had already paved the way for the rest of us geeks to follow.  Long live sharing :)

CIRCUIT PARTS:

- NE555P Timer IC (or any 555 Timer IC)
- BC547 transistor (or any NPN transistor)
- 2 X 0.01 uF ceramic capacitors (No. 103)
- 1 X 0.001 uF ceramic capacitor (No. 102)
- 2 X 1K Ohms resistors
- 1 X 10K Ohms resistor
- 5K Ohms potentiometer
- 1.2V X 6 AA NiMh battery brick
- Assorted breadboard wires
- Alligator cables

ADDITIONAL ITEMS:

- For the AM radio, I used a Panasonic portable radio. I was able to hear my voice when the volume was all the way up. This radio has a nice tuning feature. Once it senses a strong transmission on a given frequency, it lights up a red LED. There are audio signs that can clue you in such a sudden drop in noise at certain pot turns. This is how I knew my circuit was working even when there was something wrong with my audio transmission at the beginning. As soon as I powered up my AM transmitter and tuned in to 600Khz on the radio, I would tune in with the 5K pot on my transmitter circuit until the radio noise subsides significantly and the tuning red LED comes on.  Once I fixed the audio problems, I could hear my voice on the radio. It's very lo-fi but it works. Check the video to see how it sounds on my radio.

- For audio input, I used a condenser microphone with 1.5V battery power supply. These mics come cheap. I bought one for $5 a while ago. I used the alligator clips to connect the mic's male plug to the circuit's audio pins.

- I also used cheap headphones to listen to signs of a successful transmission without any distracting external noises getting in the way. And unless there's no one around you, the noise coming out of the AM radio can be quite annoying, especially when you pump up the volume while hunting for signs of your AM transmission.

Please note this circuit is by no means an example of good circuit design, but it's an example of the resourcefulness of its original designer(s). There are far better circuit designs for AM/FM transmission. This is simply a fun project and it must be treated as such.