555 Timer Radio Receiver

Changes have been made to this instructable, these changes are denoted by asterisks ( * )

A single station 555 timer radio from a few simple and common parts. Switches between an oscillator and AM radio receiver. A few things I should warn you about before you get too excited...

1. This is a simple circuit I built by accident, it does not mean it is the best way to build it.
2. I'm still new to circuit mathematics so it have a few problems or calculations that could help find a better solution for this circuit.
3. It's currently a single station radio (I don't actually know the range because I think I live within a 1/4 mile of the station I'm receiving from)
4. It's really static-y and voices are a bit garbled (the first time it worked i thought it was just the capacitors discharging and having the trimmer resistor in between resistance values), I believe you can get it in a better quality with a few more electronics but i haven't tested that theory out.

If you can help me in any way, leave a comment and don't leave comments that don't actually help any other readers reading this instructable.

Also note: I do in fact know the pics are pretty low quality, I'm still getting used to my new camera.

Step 1: The Parts You'll Need

*3 resistors - *220 ohm, *100 ohm, *1 Megohm
*3 capacitors- 2 x .01 microFarad, *10pF ( .00001 microFarads = 10 picoFarads) You can use a 10 microFarad capacitor if you do not have a 10 picoFarad capacitor (you can get them in a value packs at Radio Shack)
approx. 6 or more inches of single solid-strand wire (or an antenna)
1 LED (optional)
1 555 timer IC chip
*2 trimmer resistors or potentiometers- (It's ok if this isn't exact) 83 kilohm
*1 8 ohm speaker (not a 'beeper', a piezospeaker will work but it's not really worth it because it's very quiet)
1 9v battery and 9v battery connector (note: What I'm using is a 5v (wall) power supply from a different breadboard but a 9v will do just fine)

Step 2: Putting It Together

Let me remind you the pin with the dot/depression next to it is the 1st pin and you will count counter-clockwise around the board to the 8th pin (across from the 1st pin).
Below is the actual schematic for the circuit.

Ok first to start off, we'll apply our power and ground to the respective 8th and 1st pins. *After close inspection of a rather dangerous difference in circuit functionality I found it urgent to add that if you're using a 9v battery you need to put a trimmer resitor or potentiometer between the positive side of the battery to either the power rail on the breadboard or to the 8th pin on the timer chip due to the fact that a 9v will begin to heat up your 555 timer chip incredibly fast, and if left exposed to the overdose in voltage, could lead to a burned out chip or fire. All you need to do with this "power trimmer" you just need to resist enough voltage for safe operation (trimmer should resist about 1.8 ohms). For this step you may want to use a multimeter, but you don't NEED one to trim it well, simply place your finger on the chip when you apply voltage and use a screwdriver to trim the power down (increase the resistance of the trimmer). If you're voltage is too high you will burn your finger so i suggest having cold water somewhere nearby for that. You will also need to disconnect the power and turn up the resistance and let the chip cool before trying again.

Next we connect our *220 ohm resistor to our power (you can also use the 8th pin) and 7th pin. Then connect the 100 ohm from the 7th pin to the 2nd pin. Then connect a jumper wire from the 2nd pin to the 6th pin.

Third we'll add the *10pF capacitor to the 2 pin and ground.

Fourth we take our .01 microFarad capacitor and connect it between the 5th pin and power.

After that we will connect a jumper wire from the center pin of our trimmer resistor/potentiometer to * the 4th pin. Then we connect one of the other two outside pins of the trimmer resistor to *ground (either trimmer pin will work).

Before adding the fun stuff we will need to connect our *antenna (which allows the radio to work without having to touch the circuit physically) to the 4th pin by way of a .01 microFarad capacitor as then connecting the 1 Megohm resistor to the 4th pin and power.

Finally we connect our speaker and LED to the 3rd pin of the 555 timer chip by way of jumper wires and connect the two negative terminals to ground.

EDIT- Added two paragraphs: Alright so I've received a comment about needing to explain how this works. I can give an explanation as to how it works but it's not the most likely to be right. You may wonder "Why?", which I simply by saying, this is the first 555 timer radio I've found on the internet and I'm not the most advanced electronics person so I'm still learning the ins-and-outs of this circuit. Therefore I'm giving only my GUESS as to how it works. (To those can explain this better please post comments so I can get this following statement corrected).

Theory:
  Starting off this circuit a simple astable multivibrator, essentially it creates a tone in a certain frequency (controlled by the resistors) and a certain octave (by the Trigger pin capacitor). the other pins serve as different "effects" for the output (by changing how the internal components of the chip work together), an example that I newly discovered, using a 100 mf capacitor on the threshold pin (pin 5) in a multivibrator circuit you can create a half-siren (it "fades" the tone in and mantains a tone level afterwards). But enough about effects let's get back to the theory of operation. Stated above the circuit is based of a multivibrator which operates as a certain tone (which according to the calculation F (frequency) = ((1/.693(R1 + 2*R2)C1)/1000000) ) is 343 MHz at this point, but more is to come for this signal. The .01 microfarad capacitor, to my knowledge, doesn't do too much to the circuit's output except to make it slightly more even and less static-y. The true magic comes from the reset pin (pin 4) which connects to an antenna, capacitor, and resistor. The antenna, of course, gathers the signal received from your fellow radio station  and this signal is temporarily stored in the capacitor which acts as a low-pass filter (I'm pretty sure it's low-pass) to take out some of the high pitched signal sounds, and apply the lower tones that we can hear. The resistor and tuning capacitor (which I still think is just a potentiometer) act as a tuner. How you may ask? By taking in a microvolt of the battery voltage (assuming it's a brand new battery you may have a 9 microvolt power supply to the reset pin which i believe keeps the pin in a short reset mode and as the tuning capacitor is tuned the resistance changes, which is apparently in parrallel with the Megohm resistor and the voltage across the pin is therefore approx. half the total resistance. Now this oscillation between reset and signal ( I think) happens fast enough that it sounds connected (think of it as if you took your tv and muted and unmuted the sound at a fast speed, that's pretty much what I'm saying here, you may not notice the difference because the difference in sound and silence would slip by our brain's interpretation speed). Now you may be asking "Well, what does the multivibrator have to do with this signal/no-signal thing and how are we able to hear the sound if it in the Megahertz band?" I'm glad you asked because it's rather simple, remember that Megohm resistor on the reset pin? Well that resistor is somehow connected to the trigger pin (judging by the influence it played in other cases of multivirbators I believe that's correct) and rest of my theory trails off there becuase I really don't know how that would work out, but if that's correct that would take the 343 MHz down to about 343 Hz. then the extra capacitor on the antenna brings the octave up. The capacitor acts like a basin and your voltage acts as a water tap, if the water flow stays relatively the same, a kitchen sink being smaller would fill faster than a bathtub, and as the capacitor's value gets smaller it charges faster, thus bringing the octave up. The last bit of how the multivibrator is relevant to the circuit is this, the now 3.43 kHz signal coming from the output pin can be described as a range the speaker can put out, like how bugles have different ranges for the different keyed instruments the range of the multivibrator changes what we can hear and what we can't hear through the speakers, the latest configuration gave me the best results for listening but it may need some more tweeking, though there may be some some problems with raising/lowering the range beyond good listening levels.

Sorry, that took so long to read but that's as detialed as I could think of to explain how it works.


Step 3: Testing It Out

All you have to do is connect your power and ground to the respective terminals of the 9v battery connector. If you're lucky you will get an AM radio signal in a crackly fashion over your speaker. Like I said before, it definitely needs improvement, so leave a comment and I'll change it as soon as I can.

Tip: I got a fairly good signal by tuning my trimmer to 55.5 kilohms.
The reception will be pretty much the same throughout a building but you will need to do a LOT of work positioning the antenna ( works almost like positioning rabbit ears)

(I'm trying to put a video of it working here but I'm having trouble, I'll put it in as soon as I can.)

If you aren't so lucky and can't get a radio broadcast on it, it still works as an oscillator, you may need to pull switch some things around to get a nice frequency that you can see working. I recommend pulling the 1Megohm resistor and just connecting pin 4 to power.
If you want to learn more about 555 timer circuits you can go to the following site.
http://home.cogeco.ca/~rpaisley4/LM555.html

If you want to try and get other radio stations I suggest you read the info at the following site as well as the one above so that you can tune your radio to different stations. This is unconfirmed but I have tried other frequencies from the low AM radio bands to high FM bands but i still get the same signal, so if you get different stations let me know and I'll add that here.
http://electronics.howstuffworks.com/radio-spectrum1.htm

Changes made on the potentiometer position (July 26th, 2009) is credited to 8bitprodigy

Happy building!

source: http://www.instructables.com/id/555-timer-radio/