Two 16F84 pics using one piezo?

[Ingvar]

Try making the pin INPUT right after each soundgenerating command.
You might also get away with connecting it PortA.1-capacitor-piezo-PortA.1(on other pic). This will only work if both pins are outputs and it has the potential to make very interesting sounds if both pics try to beep at the same time.

[Ron Marcus]

What would happen if you attached one pin to the center part of the piezo, and the other to the rim? When one is sending a tone, the other will be either at gnd potential, or b+. When the sending PIC changes, the same would be true of the other one. Even if there is a conflict where both were sending, the piezo would act as a mixer and create some wild effects. Just a thought...

[Ron Marcus]

Duh, Sorry Ingvar, I just duplicated part of your post.

[Ingvar]

Yeah, i got that "déjà vu" when i read your post.

It must be a good idea since we both came up with it. Now all we need is that Rubicon actually tries it and reports back what it sounded like.

/Ingvar

[sougata]

Hi everybody,

That's an interesting option posted by ingvar. However if both the PICs are in output mode then there can be current rush through (even with the capacitors in series with the pin).

Regards
Sougata

[Rubicon]

Thanks for all the reply posts.

Ingvar was right on the money with "Try making the pin INPUT right after each soundgenerating command."

I'd originally had TRISA = %11100, PORTA.1 an output but had changed it to an input before my original post. That had made the first startup beep go. Having read that due to DC bias the port should be an output and idled low I'd added a line after each SOUND command - PORTA.1 = 0 but that hadn't worked. Changing it to TRISA = %11110 made it work well enough. When the LEDs reach an end at a different time there's a regular beep. If the same time there's a slightly louder beep. If I make it beep twice or more per LED bank at either end and they reach it at a slightly different time then they fight it out with sometimes a squalk or two.

I have a question also. In the manual it stated that the SOUND command automatically makes a pin an output. I wasn't sure if it makes it a pin set as input an output for the duration of the sound then returns the pin to an input or not. From the look of it it doesn't. Does this apply to all the other commands that automatically change a pins state or are there exceptions?

I haven't tried the PortA.1-capacitor-piezo-PortA.1(on other pic) setup yet and sougata has put me off a little. If it's safe for the PICs I'll give it a go.

Many thanks,

Rubicon.

[mister_e]

i can't comment on the SOUND command but if it's like PWM, sometimes the pin return to Input, sometimes to Output state so...

As producing sound is not a big job, i suggest you to build a few line routine for that. That way, you'll be able to reach the exact resonnance frequency and get the maximum SPL of your piezo.

Don't worry, the suggested method is safe.