AM radio transmitter based on 555 chip

This project demonstrates how to build a simple AM ​​radio transmitter based on a 555 timer integrated circuit. The circuit components include: a 555 timer integrated circuit, an NPN transistor, three capacitors, three resistors, and a potentiometer. This circuit is capable of generating an amplitude-modulated signal at 600 kHz, which can be received using a standard AM receiver. The range is approximately 30-40 feet.

You will build an AM radio transmitter, and we will show you how it works. When you finish your radio, it will look similar to my radio shown in the picture above.

These are the components you will need:
- 555 timer chip
- NPN transistor
- Two #103 capacitors (0.01 microfarads or 10,000 picofarads)
- #102 capacitors (0.001 microfarads or 1,000 picofarads)
- Some short wires
- Two 1kΩ resistors
- A 10kΩ resistor
- 1/8 inch (3.5 mm) female audio jack (you may have three or more wires, but there must be at least two)
- 1/8 inch (3.5 mm) male audio cable
- AM radio receiver
 - Antenna. Your antenna doesn't have to be made from an aluminum can, but an aluminum can will do
- Breadboard

Test your radio!

To test an AM radio transmitter, simply place the antenna next to your AM radio receiver (alarm clock) and tune it to approximately 600 kHz. Then adjust the potentiometer until you can hear your music on the radio. If you use all the correct component values, the device will generate frequencies between 100-480 kHz.

If you hear strange sounds (and no audio signal) while adjusting the potentiometer, it means your radio is working, but your audio signal needs configuration. Try increasing the audio signal volume.

Not working?

Is your transmitter powered on?

Is the audio signal enabled?

Try adjusting the potentiometer.

Try increasing the audio signal.

So how does this work?

Audio signals control the timing of radio signal transmission through their amplitude. This is called amplitude modulation (hence the name AM radio) (see diagram above).

However, as kr.baker points out in his comment, "The audio is being 'modulated' on the RESET pin of the 7555. This means the signal is turning the carrier completely on or off, rather than linearly modulated. Therefore, the audio will be distorted." He raises a very good point that I had barely considered, or not considered at all. You are not modulating the signal as you would normally. Due to the lack of 'linear amplitude modulation,' the audio quality will be significantly distorted. - kr.baker

You are not transmitting AM radio frequencies.

You are transmitting at a low frequency, which can be heard at higher AM frequencies. Let's say I transmit music at a fundamental frequency of 300 kHz (KHz), which can be heard at frequencies such as 300 KHz, 600 KHz, 900 KHz, and 1200 KHz. This is called harmonics. When a radio receiver picks up a 300 KHz signal on the 2400 KHz band, the signal will be barely audible. If you pick up the same 300 KHz signal on the 600 KHz band, it will be exponentially stronger. This is why harmonics are only useful to a certain extent.

Modify your radio

I'd like you to modify your radio and post a comment below telling us what you did and how it works! It's that simple!

However, I have some suggestions:

Try changing R2 to a 3.3 kΩ resistor.

Try removing C3 from your circuit.

Try connecting the radio antenna to ground using a 1kΩ resistor.

Our radio transmitters can only transmit frequencies from 110 kHz to 480 kHz. The AM radio band ranges from 520 kHz to 1610 kHz. Harmonics are crucial for being able to hear the audio signals transmitted from our radio transmitters.