comparator wave

[sifirzero1]

Can we generate 19khz square wave with 12F629 comparator? I don't know how to write the codes. Can you help me?

[temtronic]

No, the comparator is an INPUT peripheral not an OUTPUT peripheral.
You'll need to choose a PIC that has a 'CCP' peripheral
or
you 'might' be able to use TIMER1 to 'toggle' an I/O pin.
Much depends on what else the PIC has to do, as it has a very small amount of memory.

[sifirzero1]

They produce a square wave in the datasheet.

[temtronic]

It's not a 'free running square wave', like an oscillator. The comparator set's or clears the output based upon the conditions of it's 2 inputs. (it's a 'special' form of opamp ).

You cannot configure it as an ' oscillator'.

You can however configure TIMER1 with a preload of 65483, if the clock is 4MHz and that would generate an interrupt at 19KHz. Inside the ISR, you 'toggle' an I/O pin and that will have the 19KHz square wave.
Pretty sure that's the correct 'preload' value. this is from my 70 year old memory. CCS supplies lots of examples in the 'examples' folder, has to be a one or two in there.....

[sifirzero1]

The 19khz square wave processor we produce will not break down when other operations are performed.

[sifirzero1]

Can we measure frequency with timer0? Is there sample code.

[temtronic]

CCS supplies an example, using timer1 you might be able to modify for timer0, though it depends on which PIC you want to use.
You can also use Google to search.

[sifirzero1]

Can you make an example with 12f629? thanks

[Ttelmah]

Take a deep breath.

It is perfectly possible to use the internal comparator as the inverting
amplifier for a simple RC oscillator. However there is really no code
involved. The frequency and operation are completely dependant on the
external RC components added. The only programming is to setup the
comparator as a two input, single output unit.
To work reliably you need to use both inputs, so you can add hysteresis.
So Cout is fed to a resistive divider feeding part of the signal back into
the C+ input. The output is then fed back via another resistor to the C-
input, with a capacitor to ground.
The only code is the single line:

setup_comparator(A0_A1_OUT_ON_A2);

It is the top circuit here:

[url]
http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/square.html
[/url]

Using the PIC comparator.

The frequency is set by the feedback resistor and the capacitor, with
the voltage this has to charge/discharge over, set by the resistive
divider. So the values of all four components tweak the value.

You can use this without the C+ input, but the frequency then depends
on the hysteresis of the PIC itself, and this varies massively from chip
to chip. So though it can work it is very unpredictable in the frequency
it gives.

[sifirzero1]

I got the frequency. I have a little question. How can I control the frequency shift with timer0.

[temtronic]

hmm, never really thought about using the comparator by itself ! Sure seems like it is a waste of 1/2 the I/O pins of that PIC though.
And no 'computer control' of the frequency.

[Mike Walne]

[sifirzero1]

[sifirzero1]

[temtronic]

Most 'frequency counters' using PICs that I 'Googled' ,

like https://www.best-microcontroller-projects.com/pic-frequency-counter.html

use BOTH Timer0 AND Timer1.

Now if BOTH timers are available, you should be able to modify one of the dozens of frequency counters already on the Internet.

You'll have to edit the code for whatever clock speed you're running and send the result , via RS-232, to a PC terminal program. With an 8 pin PIC, -2 for power gives 6 I/O, -1 for the incoming signal, leaves 5 pins,which means you can't use an LCD module , as they need 6 or 7. You also have limited memory (code space), but it should be possible to run in that PIC.

What is the maximum frequency that you need to read ?