AM Radio using 555 timer IC

[rpk]

Eric, as a retired electronics tech I want to tell you this. When I was around 14 y/o another kid inspired me and I started repairing tube equipment form parts I salvaged from discarded TV, s and the like. I used to ride around either collecting tubes from junk equipment and using them to fix stuff in my home and then pedaling my bike to other peoples homes fixing their stuff. I would take my newly acquired tubes down to the local drugstore to test them. After tech school I started working at Digital Equipment Corp on main frame computer systems. I always enjoyed my job, I never hated going to work because it was so much fun. And at 70 y/o it's still fun. Now I fix Reel to Reel tape recorders for collectors. I use a Navy USM-281A HP oscope and a few Heathkit's that I build, a VTVM with a real tube in it, and a signal generator that I recently upgraded the circuitry in. But my favorite scope is a Tektronix 465. I hope you enjoy your hobby / career as much as I do mine and that you are able to inspire other young people to develop an interest in this creative field. I've always view electronics as the only real magic. As we used to say when someone asked us how television worked, we would answer it's IFM. It's F-ing Magic. Magic at an atomic level too. With electrons kicking one another around in a circuit. My Best wishes to you.

[itisonlyadream]

Good job of thinking outside the box. I've seen the old 555 used for almost everything, but I think this is a new application. The folks who want to see the schematic should go to your blog.

[picobyte]

That's the weirdest use of a 555 I have ever seen :)

[fidelcatsro]

2011- Nope
2012- Not yet
2013- No show
2014- On hold
2015- Still pending
2016- Hold your horses!
2017- Patience amigo!
2018- Stop asking!
2019- Get the hell out of here
2020 - Finally showed up on my recommended list!!

[AxelWerner]

Having people talking and a Pianist playing the piano to you whenever i want, without being in the same room ?!?! That's just MAGIC!! Whats next? Moving pictures??? 😁

[carmelpule]

My congratulations on the use of the 555 for this project.    It appears that you have a voltage controlled  pulse width modulator whose gain depends on slope with which one is comparing the  analogue voltage..  Perhaps if you demodulated before you changed  to  pulses rather  than keep the  biased carrier to trigger the slope, well, I wonder.
Still congratulations and  I hope you won  the competition.

[paulgrodkowski]

Hi Eric !

One of the most elegant home-built am sets I have seen !

[ao]

Nice work Erik, reminds me when I was at your age, no 555 at the time but premature OC type transistors like OC72, I'm talking about 50 years ago when I made my 2 transistor portable radio from scratch, having minimum possible equipment to do the impossible, I wish I had that radio today,  but that is just a wish.

[Patchuchan]

Most unusual use of the 555 I've ever seen.

[jeecodetv]

Woow. It's beautiful. Now I already know that 555 timer can be used to create this simple am radio.

[ayis]

classic 555 gives a classic radio! What else?

lovely....nothing better than the AM sound!

[jozefbubez]

The 555 timer since its introduction some 50 years ago has been grafted into all kinds of circuits. That said, a schematic would be good. Cheers and thanks!

[migalito]

You ought to build the receiver's complement. The AM 555 timer audio transmitter.

On mine I used a 560 pf capacitor that is in series with a 1.5 k resistor for R2 and a 1 k resistor for R1. By rights this should have placed the oscillator at around 680 Khz but my receiver that picked up the signal saw it just above 800 Khz. Later I will actually measure the frequency. I thought the discrepancy might be due to tolerances but I measured the components and its not.
For the audio modulation my idea was to superimpose the audio on the + lead from the power supply. To do this the circuit used must be linear similar to two batteries in series. What I did was use an audio transformer. I ran the + lead from the battery I used to one of the taps on the high impedance side of the transformer and ignoring the center tap I mapped the other tap on the high impedance side of the transformer to the Vcc input on the chip at the point that branches over to the subcircuit containing R2, R1 and the 560 of capacitor. The low impedance side of the audio transformer is connected to the audio source such as at the headphone jack. With this arrangement you get both isolation, and the superposition of the audio onto the Vcc voltage.
The audio from this method is quite good. I built mine to play audio books when I am far from the house and don't want to carry an expensive tablet. I've seen others try to use pin 4 and 5 ie reset and control and they kind of got some kind of modulation, but it was not understandable at all.
I just posted a video of my 555 audio transmitter on YouTube and if you do a search you can find it and hear the sound quality for yourself. The audio in the video is from a metronome, but its equally clear with music and voice too. I do have a low pass filter at the output to cut out harmonics and that is why you see the shape of the signal on the scope.

I took everything off the breadboard and I soldered all the components to a perforated board earlier today, but before I build the enclosure I am adding two more things and they are: 1: A small trimmer cap in parallel with the 560 cap or else a variable resistor in series with R2 and R1 to give some tuning flexibility. 2: I am adding or would like to add a RC network of 3 caps and resistors to change the output from square wave to more of a sine wave although it sounds awfully good as it is.

I like your receiver and will probably give it a go later.

Good luck in your contest but by now it must be over for sure since your video was posted in 2011 and this comment is from 2019.

[ZenPunk]

that little substitution effect in the beginning freaked me out the first time...clever!

[AtomicElectronCo]

nice use of a if it would make as good a transmitter?

[waaos]

when adjusting an inductor you may find a plastic or non-conductive screwdriver to be more helpful since the iron in the metal screwdriver will interfere with the tuning. 

[keithsilvers]

jst wondering why did you not try to put a on/off swicth in?

[chronobot]

It looks nice and sort of works.

Getting a 555 to work in this way is impressive nonetheless.

[brandonlaragirl]

Awesome radio bro. I have a question. How many more windings do I need to do or do I need to just add more capacitance to my coil to receive higher frequency bands. Above 1.8 MHz if I just keep adding capacitance will that do the job or do I need to wrap more magnet wire around my coil?

[CoolDudeClem]

I built this circuit but can't get it to work, I can't tune in to any stations at all, but when I adjust the bias I get a loud high pitched shriek, any idea what could be wrong? I checked for solder bridges and continuity and that all checks out to be ok.