Vintage Push Button Radio conversion

[bigk29]

Hey Everyone,

Just looking for some help with a little project that puts a little twist on an AM Radio.
While mostly everything I have researched shows that a vintage radio can be converted, none of them use the existing push buttons to change a value in the Arduino.

So, the push button slides an Iron core through a coil to change the frequency.  I want to incorporate that inductor in a circuit that will allow me to use an FM module on the arduino.

My lack of electronic knowledge limits me. 

I know that an RC circuit can do this, but I don't know how.   
I have also looked at using a  metal detector type circuit, but because the whole radio is metal, I think there would be too much noise.

Converting the actual frequency to the Arduino isn't necessary, only that the Arduino can detect the variable states in change of the inductor using the push buttons.

Any thoughts?
Thanks

[Grumpy_Mike]

You can make the coil part of an oscillator and measure the frequency, add a capacitor so this arrangement works at the resonant frequency. Use a resistor in the ground connector of the oscillator to measure the current this oscillator takes by measuring the voltage across this resistor..

When the core is introduced into the coil the resonant frequency of the system will change and so will the current the oscillator takes.

Alternatively use an IR LED and photo transistor and mount it so the moving of the core breakers the beam.

Alternatively mount a magnet on the end of the core and have a reed switch or Hall effect switch to detect when the magnet comes close.

[zwieblum]

Measure the inductance of the coil with the arduino, that should work quite nice with this arrangement.

[GoForSmoke]

I had a little Sony AM radio in 1968 that I kept until I got FM just a few years later. It used a DIAL to tune to channels and another for volume control. The only switch was ON-OFF. From outside you had the switch, volume, tuner and a display of frequencies with a red needle showing where the tuner was set.

[Robin2]

So, the push button slides an Iron core through a coil to change the frequency.  I want to incorporate that inductor in a circuit that will allow me to use an FM module on the arduino.

Pleas post a picture of the push-button mechanism. See this  Simple Image Guide


If you could fit a micro-switch behind each button I reckon the whole thing would be a lot simpler.

...R

[bigk29]

Thanks for the replies everyone!

@Grumpy_Mike - Your first idea is what I was thinking of because it allows you to use the tuner knob to the desired 'station', and then allows you to use to still use the mechanical memory buttons.

So for the circuit you described, does it matter how big the resistor and capacitor?  

The radio has three coils, two have two separate wires wrapped around the cardboard tube, and the last coil is just one.  I was going to use the last tube with the one wire wrapped around the tube and isolate it.

separte@zwieblum - I had looked at that circuit, but the schematics that I viewed also added an additional chip to get it to work.  

I am going to try and post a picture..

[Grumpy_Mike]

So for the circuit you described, does it matter how big the resistor and capacitor

Yes.
The resistor should be small but big enough to drop a measurable voltage when the oscillator is running.
The capacitor is for changing the frequency and putting the oscillator at the resonant frequency. It will normally form a resonant frequency with your existing circuit. However, what I described will just give you an indication that the button is pressed. It seems like you want to use the analogue information given by the amount the coil's core is inserted into the coil.

That is possible by using the voltage drop, but I would keep the front end circuit of the AM radio running and just measure the frequency of this oscillator. It is likely to be the frequency the radio is tuned to minus the local oscillator which is normally 470KHz. You can then do a simple mapping with this result to derive your FM frequency.

[GoForSmoke]

I would just sense button presses and use the FM module to receive radio.
The coils are inside the radio, unseen, can they be used with the module (I ask incredulously)?