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Thread: FREQOUT 4mhz

  1. #1

    Default FREQOUT 4mhz

    I want to drive a piezo buzzer which I haven't done before. Read where FREQOUT may have issues with a 4mhz oscillator?

    Goal is to drive one of those button piezos at 6500 hz. Just thought I'd ask before attempting whether there will be problems.

    Will I need a driver circuit as well or can the pic drive a piezo directly ? -- THANKS

  2. #2
    Join Date
    Oct 2009
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    539

    Default Re: FREQOUT 4mhz

    If its one of those small 3v - 15v type piezo buzzers then this can be driven directly from the PIC



    Some further examples and reading http://www.picbasic.co.uk/forum/showthread.php?t=3076

    Can't really help with the frequency part, the buzzer I use as an alarm just runs at whatever its internal frequency is when DC voltage is applied

  3. #3

    Default Re: FREQOUT 4mhz

    It's not a buzzer, it's just a transducer. And like I say, FREQOUT (according to manual) is limited at 4mhz and would like to know more.

  4. #4

    Default Re: FREQOUT 4mhz

    Ok -- good link -- I'll try the PWM command instead.

  5. #5
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    Default Re: FREQOUT 4mhz

    I seem to recall the FREQOUT command is only accurate at 4 MHz. If you're clocking at 8 MHz, divide the value by 2 (and so forth). The command itself should work at any clock speed. Just take into account any divisor needed to achieve your 6500 Hz.

    If you have Mister E PIC Multi-Calc, you can use the Timer Helper to create any frequency the processor is capable of, and at any chosen Fosc.

  6. #6
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    Default Re: FREQOUT 4mhz

    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.

  7. #7
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    Default Re: FREQOUT 4mhz

    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.

  8. #8

    Default Re: FREQOUT 4mhz

    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 ?

  9. #9
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    Default Re: FREQOUT 4mhz

    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).

  10. #10

    Default Re: FREQOUT 4mhz

    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.

  11. #11

    Default Re: FREQOUT 4mhz

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

  12. #12

    Default Re: FREQOUT 4mhz

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

  13. #13

    Default Re: FREQOUT 4mhz

    I think it may be this crap piezo I'm using --

    https://www.ebay.com/itm/US-Stock-50...72.m2749.l2649

    hard to work with. maybe someone can suggest an inexpensive one that they know works well. need low cost as this may be a product idea. 6500 hz is pretty high as well.

  14. #14
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    Default Re: FREQOUT 4mhz

    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
    This is more entertaining than Free to Air TV

  15. #15

    Default Re: FREQOUT 4mhz

    Ok Richard thanks. I'll try SOUND and stick with it and yes, those transducers are something I've never dealt with -- they're a pain. Going to try something else.

  16. #16

    Default Re: FREQOUT 4mhz

    Do you think these will work on a PIC output with the SOUND command at 2300 hz ? At least they're 5V.

    https://www.ebay.com/itm/Gfortune-15...UAAOSwErFZ0-ze


    Having problems getting piezo diaphragms and driver circuits to be very loud. barely hear them in fact. --Thank you

  17. #17

    Default Re: FREQOUT 4mhz

    Those are self resonating. They will buzz at 2300hz when 5 volts is applied. Look for "transducer".

    Something like this
    https://www.ebay.com/itm/AT-12-Piezo...gAAOSwZd1Vewuj

  18. #18

    Default Re: FREQOUT 4mhz

    I realized that after posting -- thanks. Will try that part you suggested. Can't believe something so simple has been such a headache.

    Thanks.

  19. #19
    Join Date
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    Default Re: FREQOUT 4mhz

    Just to try a piezo to see if it works, just use the HPWM 1,127,2000 command and connect your piezo to the PWM output. I found some processors the SOUND command doesn't work so well for. I would be chasing my tail trying what you are with what I was working on.

    Once you know the piezo is good for a PWM output, then work on the SOUND software. My opinion, and I reserve the right to be wrong.

  20. #20

    Default Re: FREQOUT 4mhz

    Quote Originally Posted by Michael View Post
    I realized that after posting -- thanks. Will try that part you suggested. Can't believe something so simple has been such a headache.

    Thanks.
    It also helps to place a 1K resistor in parallel with the transducer when driving with a logic signal. Like the others said use HPWM. Sound and Freqout are blocking commands.

  21. #21
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    Default Re: FREQOUT 4mhz

    You could eliminate any doubt with the pic by oscillating port b yourself,
    and connecting an LED to any of the other port b pins, and changing the delay value.

    Code:
    buffer var byte = 0
    TRISB = 0
    
    cycle:
    
    if buffer == $00 then
    buffer = $FF
    else
    buffer = $00
    endif
    pauseus 1
    PORTB = buffer
    
    goto cycle

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