FREQOUT 4mhz

[HenrikOlsson]

From the manual:

FREQOUT works best with a 20MHz or 40MHz oscillator. It can also work with a
10MHz or 8MHz oscillator and even at 4MHz, although it will start to get very hard
to filter and be of fairly low amplitude. Any other frequency will cause FREQOUT to
generate a frequency that is a ratio of the actual oscillator used and 20MHz.

For simple beep type of tone from a piezo buzzer just use PWM, HPWM or "manually" run the (E)CCP module.

/Henrik.

[Art]

FREQOUT can do dual frequency (polyphonic), and that is a mess at 4MHz.
DTMF works the same way, but I’ve never had a telephony system understand it for a pic clocked less than 20MHz, no matter what I do.
For a single frequency it might be ok, but as said, PWM is non-blocking, can make the sound forever, and a much better choice for a single audio freq.

[Michael]

I may have to use PWM as it appears FREQOUT won't function with my antique 16C72. (I have a boatload of them).

The 16C72 is 8bit.

We'll see -- thanks -- will get back to you no doubt.

Also using a 2N4401 to drive the piezo, would imagine I need it ?

[Art]

I wouldn’t say “need”.
You’d get best results using any of the shrouded ones that will at least be loud at their resonant freq. That would be money better spent than on the transistor I think.
The pic could probably drive a small speaker through a series capacitor. I used a MAX232 as a buffer for a speaker, and small output transformer (MAX232 drives the audio positive and negative).

[Michael]

Not having any luck. I know the piezo is good -- I've tested it.

I'm probably missing something in set up or some register that needs to be modified?

I just put in --
PWM portc.4,50,6500

Piezo is 6500 hz. Hearing nothing.

PIC is 16C72, 8 bit antique.

[Michael]

Don't know if PWM is my only option. FREQOUT can't be used and SOUND is a sine wave right?

[Michael]

and that should be 127, not 50 for duty cycle -- typo

[richard]

Don't know if PWM is my only option. FREQOUT can't be used and SOUND is a sine wave right?

wrong
from manual

SOUND outputs TTL-level square waves. Thanks to the excellent I/O characteristics of the PIC MCU, a speaker can be driven through a capacitor. The value of the capacitor should be determined based on the frequencies of interest and the speaker load. Piezo speakers can be driven directly

I just put in --
PWM portc.4,127,6500

Piezo is 6500 hz. Hearing nothing.

pwm does not do what you have expected

@4mhz clock pwm output is 6500 cycles @200 hz


a 6500hz resonator can be driven at frequencies other than its resonant frequency

your chip has a pwm/ccp module , you could use HPWM

to get maximum noise you can drive the resonator bipolar mode between to output pins antiphased

I notice those resonators you linked have no connecter leads , how good is your soldering ?
they don't work if they have been cooked