my digital station changer [help]

[mstechca]

alright, I have come to determine that the digital station changer that I made has effectively altered the frequency (without pressing the button at all). Sometimes, I replace the button with a wire and connect the hanging end of the wire to ground as if I was pressing a button.

What I have noticed is that the longer the wire, the longer the unwanted "antenna". As soon as I cut the wire in half, the frequency all of the sudden changed.

All that time, the wire was connected to the clock pin of the 4024 and also tied to a 27K pull-up resistor.

I tried changing the resistor to 1.8K. The wire this time did not act as an antenna, but I cannot change stations when I press the button several times. With the 27K resistor, I can change stations.

Do you think a capacitor, as well as increasing the resistor value will help me?

It's probably something simple with digital electronics I am not aware of.

 

[Nigel Goodwin]

It's probably something simple with digital electronics I am not aware of.

How can it be something you're not aware of?.

EVERYONE who has replied has told you repeatedly, IT WON'T WORK!.

Why do you have trouble understanding that?.

Audioguru suggested a method that WOULD work, use the same digital setup to switch resistors, and use the voltage from them to alter a varactor diode (nice call Audioguru!).

 

[mstechca]

Nigel, you must have not been experimenting with the 4024 chip at all.

If I can get the chip to change radio stations, all I can see it being is the matter of adjusting or adding a component to the clock pin of the chip.

If anyone else has tried to make a digital FM transmitter, tell me about it.

the only thing I can do now is use no wire leads and pray to god that the station changer works, with all components on PCB.

I do not want to add extra resistance to my digital circuit (as audioguru suggests) because I believe it will reduce (at least) range.

 

[audioguru]

I think the CD4024 counter IC is counting many clock pulses with each push of the button due to contact bounce. The clock input needs a debounce circuit.
I also think the CD4024 counter IC will power-up in a random count pattern because it doesn't have a power-up reset cap and resistor.

If you think God will help you make your circuit work then you could wear black clothing and walk across a busy highway at night.

 

[chemelec]

It is one thing to Ask for Help. It is another thing to LISTEN when help is given.

If you don't want the help, Don't Ask for it.

mstechca, Sounds like my X Wife.

 

[Nigel Goodwin]

Nigel, you must have not been experimenting with the 4024 chip at all.

No, never used one, but I understand what it is and how it works.

If I can get the chip to change radio stations, all I can see it being is the matter of adjusting or adding a component to the clock pin of the chip.

As EVERYONE has told you, it won't work, it's not switching the capacitors IN and OUT, it's merely switching them to logic levels. It will have some unpredicable effect on the tuning, but you've already found that!.

If anyone else has tried to make a digital FM transmitter, tell me about it.

Many people have, but they do it properly!, using a PLL and crystal control.

the only thing I can do now is use no wire leads and pray to god that the station changer works, with all components on PCB.

There's no way it can work properly, because the original design is completely flawed.

I do not want to add extra resistance to my digital circuit (as audioguru suggests) because I believe it will reduce (at least) range.

You believe (as usual) completely wrong, as already suggested lookup varicap or varactor diodes, you use the voltage from the resistors to change the capacitance of the diode. As Audioguro kindly pointed out, you don't require specific varicap diodes, any reverse biased diode will do.

 

[mstechca]

in that case, I'm on my own.

 

[Roff]

Have you found Harry's Homebrew pages? If you follow the links to his transmitters, you will find a couple of good examples of varactor-tuned FM transmitters.