Here you goView attachment 91123

I redrawn the circuit, it's more easy to see as the normal schematic.

 

I redrawn the circuit, it's more easy to see as the normal schematic.

View attachment 91158

The original schematic gave the impression that battery negative/pin 4 were floating - as in isolated from the earth associated with the tuning coil.

The circuitry around pin 7 made more sense that way.

Anyone thinking of trying it should note that the CMOS 7555 specified is just about fast enough for the MW broadcast band - the old bipolar 555 probably won't even manage the LW BCB.

 

The original schematic gave the impression that battery negative/pin 4 were floating - as in isolated from the earth associated with the tuning coil.

The circuitry around pin 7 made more sense that way.

Anyone thinking of trying it should note that the CMOS 7555 specified is just about fast enough for the MW broadcast band - the old bipolar 555 probably won't even manage the LW BCB.

The pin 4 is a reset pin and it was connected to the +V.
The pin 1 is the gnd of the 555, it was isolated from the coil ground, and it was also through the VR10K connected to +V, it seems used the +V to be the ground, but it is not really, the pin 1 is not the ground here, I'm not sure will this circuit works normal or not.

 

It don't work normal its using the 7555 to do stuff out of the box I sure I posted the link to where I found it. It tells how it works.

 

Here's how it works

Here’s how the circuit works: The AM radio signal is tuned by inductor L, which is 300 turns of wire on a 1/2 inch diameter cardboard tube made out of an old toilet paper roll, along with the 100pF variable capacitor. One end of the parallel configuration of L and C connects to an antenna (surprisingly long!) and the other end connects to a ground wire which is tied to the AC outlet ground (old books tell you to ground it to a water pipe). So far this is exactly like an AM crystal radio.

The 555 timer is configured as a pulse width modulator in a non-traditional configuration. If I used the standard approach and connected the input to the CV pin, the low impedance of the pin would prevent the circuit from receiving any radio signals. I had to invert the circuit and tie both high impedance analog pins, Threshold and Trigger to the radio signal input. This is the reason why the CMOS version of the 555 timer performs much better than the standard bipolar, which has higher input bias current.

The pulse width modulator ramp is created by the 0.01uF capacitor and the 10K bias potentiometer which are connected to the Discharge pin. The potentiometer wiper goes to the LC arrangement. With no radio signal coming in, the voltage on Threshold/Trigger ramps up until it hits the threshold, and then Discharge causes the voltage to ramp down again.

When a radio signal comes in, it gets superimposed on the ramp signal, causing the threshold and trigger comparators to trip early or late in a cycle. This variation causes the output duty cycle to vary, which we can hear as sound in the speaker.

Demodulating the signal properly requires adjustment of the bias knob, so that part of the radio signal is “clipped” and ignored by either the threshold or trigger comparators. This ensures that the negative “halves” of the radio wave don’t cancel out the positive “halves”.

Want to hear what it sounds like? Check out the video below:

 

NE555 Design Contest
http://makezine.com/2011/04/21/555-contest-winners-announced/

 

It won in Minimalist

 

The pin 4 is a reset pin and it was connected to the +V.
The pin 1 is the gnd of the 555, it was isolated from the coil ground, and it was also through the VR10K connected to +V, it seems used the +V to be the ground, but it is not really, the pin 1 is not the ground here, I'm not sure will this circuit works normal or not.

View attachment 91161

Yes indeed - I was thinking of the GND pin on an op-amp.

Might've been better if I'd called it the GND pin rather than mis-remembering pin numbers.

 

I have been known to help design custom 555 circuits.

The chip is ancient, but useful, and I like it a bit.

 

I have been known to help design custom 555 circuits.

The chip is ancient, but useful, and I like it a bit.

I was going to make it just to see how it goes been digging in my parts I know I have a 7555 some where.
I figured it be cool to use a red led as a tuning cap.
http://www.hanssummers.com/varicap/varicapled.html

 

I was going to make it just to see how it goes been digging in my parts I know I have a 7555 some where.

I seem to remember an LMC555 equivalent to the 7555 - there may be other prefixes that mean the same thing.

 

I got enough parts to open a store but there mostly in big boxes, And the stuff I use is only things I have that you can find LOL. I wish I had a place to setup shop. My twins ran me out of the living room.