how to control 555 resisters with PIC

[websmith]

The timing of the 555 is a function of the current drawn from these pins. Putting a transistor or FET in ths path and controlling its base/gate with PWM via a LP filter (series resistor and cap to ground) will do the job

[KB3BYT]

to Websmith...Can you suggest some values to try....
like the resistor that is between pins 7 and 8 ... can I replace the resistor with a 2N2222 NPN transistor and connect pin 8 to the collector and pin 7 to the emitter and the PIC to the base?
Do I need to put a resister between the PIC and the base? What value?
Do I need to tie a cap to ground where that resister meets the pic? what value?

Same questions about the resistor between pin 6 and 7.

555 chips use a capacitor on pin 6 and 2 tied to ground to control frequency
oscillation.

There is a variable capacitor called a varicap and some diodes can have capacitance so is there a way to replace that pin 6,2 cap with a diode or
varicap that is tied to the PIC also?

I am a retired computer programmer and I do not know electronics as well
as the electrical engineers so am limited by the example wiring diagrams
provided by the PBP manual.
As a ham radio operator I learned a bit about electronics and I dream up cool projects but I let more smoke out of components than I'd like to admit.
It seems to me that if I can figure out how to mimic variable resistors and capacitors using the PIC commands then it would open up doors to lots of
toys for me to play with.

[Darrel Taylor]

"Anything you can do, I can do better". Said the PIC to the NE555.

I can see no reason to even attempt what you're proposing. The PIC can perform any function the 555 can do, without any external components. And do a bunch of other stuff at the same time.

It would be like using a 300hp car engine just to regulate how fast your electric can opener turns. Not that someone wouldn't try that either.
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[sayzer]

"Anything you can do, I can do better". Said the PIC to the NE555.

I can see no reason to even attempt what you're proposing. The PIC can perform any function the 555 can do, without any external components. And do a bunch of other stuff at the same time.

It would be like using a 300hp car engine just to regulate how fast your electric can opener turns. Not that someone wouldn't try that either.
<br>

I have seen people using 12C508 direct drop in 555 place upside down (different supply pins ).

Compared to 555, 12C508 provides a better accuracy over a range of frequency they say. Thus, it comes to the cost at the end.

555 is about the same price of a single general purpose transistor!


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[Acetronics2]

Just play with voltage @ pin 5 ... see 555 Datasheet for that.

Other ( read complicated for the use ...) thing to do is use the " constant current config" and drive this current with the PIC.

Broadest freq range to be expected ...

Hi, Darrel

You're not right ... or right just for "classical" designs ...

Alain / ._ ._.. ._ .. _.

[KB3BYT]

I thought I made my reasons for wanting to learn how to
control the 555 resistor and capacitor rack.
This isn't a question of how to make a PIC do something better than a 555.
Its a specific question of how to control the resistors and capacitors aligned with the 555 to make the 555
do something variable.
And again....
I'm not an electronics engineer.
I am a retired computer programmer.
So I don't always understand some of the things the electronics engineers take for granted when
designing circuits so please tell me how to wire
with more detail. All my wiring I get from the PBP manual and you know how sparce that is.

[Acetronics2]

Soooo,

In your case ... I only see digital pots ( AD 7376 i.e. ) wired in parallell to existing resistors ... or instead them.

For capacitors ... small relays parallelling other values to those existing is the only easy way I see.

Of course, The PIC will drive both ... and you might get no scale-holes !!!

Sorry for the scheme ... but I consider you've to understand what you do !!!
That's it ...

Alain / ._ ._.. ._ .. _.