how to control 555 resisters with PIC

[KB3BYT]

I can do that.
Thankyou.

[skimask]

I had the same type of thing awhile back, thought I needed to use a 555 and a pot to generate a variable freq output. I used a 12F675 and 2 buttons to make a nice square wave, one button increased freq, the other decrease freq. 8 pins, 1 pin power, 1 pin ground, internal oscillator, 2 pins for buttons, 4 pins left over, 2 pins at main freq (inverted from each other), the other 2 pins running at 1/2 and 1/4 of the main freq. Was able to adjust it from 0hz up to around 200khz. Worked like a champ, took the same amount of board space, and I suspect took less time to program that PIC than it would've to calculate the correct values for a 555 to get a 50% duty cycle square wave.

My 2 cents....
JDG

[KB3BYT]

OK OK OK
a pic can do anything a 555 can.
Again...
I ask how the right way to do this task of using a PIC to
control the resistance and capacitance of external circuits... for a real good reason.
There are lots of example circuits that show how to build discrete component projects. There must be a 1000 of them out there.
BUT
when I want to do a PIC controlling project to interface those circuits... I don't really find ANY examples.
So...
I ask here if anybody knows a good way to make the
replacement circuitry to interface a PIC where a resistor or capacitor is found in a circuit....
because its the resistors and caps that are always attached to dials with pots and variable caps.
Forgetting the 555....its all those other circuits I want to learn to interface.
I just used the 555 as the example because there are sssssssssssoooooo many web sites devoted to showing the 555 pins layout...where plus and minus and ground lays compared to the pins....so anyone could find good references.

[skimask]

Ok,Ok,Ok,...I smell what you're cooking...

Well, for controlling programmable resistors, maybe check out the XICOR type programmable resistors (X9241 for example). XICOR makes them in various values (for instance one version might start at 0K and go to 1K, another might start at 0K and go to 100K). You can control them in PBP using I2C commands (just like accessing an external serial eeprom chip as shown in the PBP manual and wired up in almost the same manner), or, for that matter, a couple of the XICOR types only need 'up' and 'down' pulses to change their resistances. I can't remember thier numbers off the top of my head.

Relatively simple-ish chips to use. I used them for voltage dividers in front of small amplifiers before. Worked good for me. And the resistance value seen by the external circuit would be completely independant of the PIC circuit controlling it (except of course for power/ground type lines).

As far as change capacitors values, like they've said earlier here, small DIP
relays switching different capacitors in/out of the circuit is about the only way to go. I wouldn't try to use a 4066 (correct number???) which is a multi pole digital switch, but it has built-in resistance due the MOSFETs in it, which will screw with the values quite a bit (I know, I've tried it).

JDG

[KB3BYT]

thanks for the info

[skimask]

thanks for the info

If you really wanted to get crazy, you could easily drive an R/C aircraft servo to turn a rotary switch connected to a bank of capacitors (ya know, ka-chunk, ka-chunk, ka-chunk) and another servo to drive a linear pot. Drive servo's is easy with a PIC also. At least you'd have something mechanically silly to watch, something a tad bit over engineered.
JDG

[Acetronics2]

If you really wanted to get crazy, you could easily drive an R/C aircraft servo to turn a rotary switch connected to a bank of capacitors (ya know, ka-chunk, ka-chunk, ka-chunk) and another servo to drive a linear pot. Drive servo's is easy with a PIC also. At least you'd have something mechanically silly to watch, something a tad bit over engineered.
JDG

Hi Skimask

before ... just learn how to fly models with old non proportionnal radios ...

THEN you can talk about all that ...

Ah ... look at the little ( humour ) difference between AD7376 and the XICOR X9xxx ...
One can be used ... and the other NOT here.

Alain

Hi, KB3

As the capacitor have one terminal to be grounded, you can use Mosfets like 2N7000 or BS 170 instead of the relays.
But it will introduce a small parasitic capacitor ... if it doesn't matter, that would be simpler to build.

Alain