[16F871] Power on RA4 before power on vdd?

[Acetronics2]

Hi, Buzz

Why not use a stupid N Mosfet ( 2N7000 or BS 170 ) to switch your Buzzer ???
It would provide all the insulation you need ...

just invert your output level ( better for Power-on response of the Buzzer... hmmmm ? ) or use a P-Mosfet ( BS 250 ) and buzzer between Drain and ground ...

Alain

PS : 13v ... doesn't make you remember something about programming your PIC ??? ... jam at sight !!!

[Buzzz]

Yes, a stupid mosfet or even a cheap ass transistor could be the solution. Problem is, that I already have a PCB, and even with redesign really no space for extra components, not even a TO92...
So that's why I would like to fix this with just a piece of wire between the (now unused) pin RA4 and the buzzer.

[Acetronics2]

Never soldered some components on your copper tracks and played with the cutter ??? ...
Time to learn !!!

Alain

PS: why not put your "piece of wire" to the 5v instead of 7v2 ??? just a track to cut ...
5v Buzzers also exist !!!

[Buzzz]

Normally, I would agree with you. I am very familiar with cutting traces and stuff (built several ground-planed spiderweb transmitters and so on ). Problem is, that this design is already completed, several PCB's have been made, and I wouldn't like to rework them all with cutting traces and stuff. Feeding the buzzer with 5V gives me too much sound-loss.
I know I am starting to be a pain in the ass, but the solution like in my opening post would suit me best. I think I am going to sacrifice a PIC, and just see what happens. The 7.2V voltage probably wont't be the problem, the only thing I am afraid of, is that the PIC might not like the 7.2V being present when the Vdd-voltage regulator is switched off. I'll just see what happens, if it fries my PIC, I probably cannot bypass the extra FET-idea...

edit: unfortunately 5V buzzers are too "quiet". I ordered like 7 or 8 different types, but I didn't like any of them...
...my demands are just way too high...

[Buzzz]

All this effort for nothing...
The buzzer appears to draw just over 30 mA's of current, even at 5V. So I will need a tranistor/fet anyways. So thanks for all your help, I am going to "spiderize" my PCB's....

[Melanie]

Why a Buzzer instead of a Piezo sounder which is cheaper, draws near no current of consequence and can be driven directly from a PIC via something as small as a 100nF decoupling Capacitor? Another consideration is some buzzers have a serious back-emf problem which will blow your PIC's I/O (or even an external transistor) in no time flat unless you add suppression (more PCB real-estate eaten away).

[Acetronics2]

All this effort for nothing...
The buzzer appears to draw just over 30 mA's of current, even at 5V. So I will need a tranistor/fet anyways. So thanks for all your help, I am going to "spiderize" my PCB's....

Hi Buzzzz

I understand ... I was caught on this, somtimes ago ... But I was lucky ( or careful ??? ) , it was just the proto board ...

Alain

[Mike, K8LH]

Just a thought -- we use miniature Soberton GT111P speakers which can be connected directly to a PIC pin on 3.3v or 5.0v products and they work quite well...

Good luck with your project... Regards, Mike

[Bob_W]

I'll just see what happens, if it fries my PIC, I probably cannot bypass the extra FET-idea...

edit: unfortunately 5V buzzers are too "quiet". I ordered like 7 or 8 different types, but I didn't like any of them...
...my demands are just way too high...

Take a look at these http://www.mallory-sonalert.com/cata...lert_index.htm
The've got a whole bunch of sounds, and all the 5 volt ones will run directly from RA4 - no diodes, no hacking, no popped PICs.

[Buzzz]

Thanks for the help and ideas! I'll go and see what will suit my project best!

[Melanie]

> unfortunately 5V buzzers are too "quiet"

I thought this way once. But trust me, if you hit the correct resonant frequency of a Piezo transducer, you'll bring the house down! Your mobile phone Ringer loud enough set to full volume? It's probably running at 3v!