555 AM Transmitter

Intro: 555 AM Transmitter

This is a very simple easy to make AM transmitter if you don't want to use inductors or capacitors and don't mind not having extreme power. The best part is everythinf you need to build it is at Radio Shack.

STEP 1: Building the Circuit

Once you have all the parts the circuit is very simple to construct (on a breadboard anyway). The simple seven component schematic is below.

A decoupling capacitor is needed for battery operation =]

STEP 2: Tunning the Circuit

Once its assembled you have to tune it and then adjust the audio in ground for optimum audio level and clarity. The pot on the left (or the one thats hooked to the IC) adjusts the frequency. It really doesn't adjust it that much ±30 kHz and is for fine adjustment only. Since the frequency is near 540 kHz sweep the radio and the right pot (audio ground). Once you hear it your done, but the radio has to be a little loud because there is no pre amp on the transmitter

STEP 3: Specs and Troubleshooting

Range: 2m
Power: 5-15V
Freq: 530 kHz - 640 kHz possibly higher

Troubleshooting:
If your tuning it for the first time do not use a portible radio it dosn't work well wit them.
If you know its getting power and you can't tune in try stepping away from it or touching parts of it to act like an antanna (I coulden't get wire to work)
Also it might not be enough amps i never mesured how many it took, but it likes computer power supplies and 9.6V packs.
If you want better audio put an inductor between the IC's output and audio in.

Comments

[PRO DR MR BOB]

What dose 2m mean is it 2 meters or 2 miles in the specs of the trasmiter

[yousef777]

mean is it 2 meters

[bo'connor1]

By portable radio, do you mean battery powered or socket powered?

[cbatenga]

What is the purpose of using a 555 ic in an am transmitter? im just curious about it, i hope you can help me.. thanks a lot.. :)

[jazzzzzz]

It acts as the oscillator. So it produces the 500 kHz for transmission.

[LSD3]

I am building remote motion/IR sensors that would simply make a 5ms transmission. The receiver converts the frequency to a 4 to 20 ma and the PLC can now assign the location of the transmission. I am an industrial automations guy and any help in the low power transmitter area is appreciated.

[jazzzzzz]

So are you using separate IR sensors going to one receiver for the PLC. If so what are the specs of the receiver. (or do you need to make that to?)

[LSD3]

I thought I would use a 10 meter base station with side band. The units would simply transmit a binary address on a single frequency much like morse code. This would identify the unit which was disturbed. I own a mountain and simply want prewarning of egress on my property. Any modulation into an Analog to digital converter could be inputed into the PLC (also existing) and grid location plotted on the HMI.

[jazzzzzz]

I had a project much like this in mind, with a computer I'm not lucky enough to have an HMI. Unfortunately the 555 maxes out at about 1 MHz. If you plan on building the transmitters from scratch there are many ways to go about it. I like building them with logic and timing IC's.(no  real reason why)
If your going IC the 74HC5555 is quite nice(89MHz at 25°C).
The problem is most IC's are going to give a square wave with a lot of harmonics and not so much power. A Colpitts or Hartley would be better. Also easy to get componants for.

Do you have microcontrollers and a programmer for the addressing?(if not i have a backup plan). Are you using a PIR sensor for detection?

[rob0t]

Hi I'm new here.
Thanks Lectric Wizard for other circuits, always good to have a few to compare.
Good job Jazzzzzz.
But I fail ;).
Audio pot:
__
[_]
| | |Ground
| \+5v
audio+

Audio- to 3.

Yes?

[jazzzzzz]

I believe I went audio + to Pin 3.
Since audio is technically AC it will depend on the audio source.
If the source crosses zero (true ac) it wont make a difference I would just try it both ways, it is the best way to be sure

[rob0t]

Mh, you'd answered!
I tried.. all the ways! I was having trouble with audio jack, which was the live pin, and what was just a pin (to fix).
The audio pot really changes volume too, which is cool.

Now, why would you think my 5v setup was not working?
Antenna problem, i.e. I was too far, and using 9v boosts anyway the signal, so I assume the 5v was for me too little (too far).
I will have to try 5v again, very close, on top of radio.
Or, 100uF cap between output& gd might help.

Cool anyway!
My first working project in MW! :)


Thanks Jazzzz.

[jazzzzzz]

I'm glad you got it working.

what were you using as a 5V source?

[rob0t]

A 5v mains adaptor. 500mA. Too low?

[jazzzzzz]

No but the ripple from that adaptor will make the 555 very angry (I assume its a charger) some decent capacitor filtering should fix that. And inductance for good measure.

[rob0t]

Forget that!
I used 9v (instead of 5v) and voila!

Cool! :)

[Lectric Wizard]

Here's a quick schematic I threw together to show how to really amplitude modulate a 555. Lots of calculators online to figure out values so I didn't bother.

[Lectric Wizard]

like this ?

[Lectric Wizard]

Are you connecting the audio "shield" to the output & the audio "hot" to the pot ? It's unclear in the schematic & may be the cause of the confusion

[jazzzzzz]

I will have to derive one for you (assuming the potentiometer is the only variable)
I will post it as soon as possible