MOSFET Question (Buzzer, Motor Drive, LED Driver) - Advice.

Hello everyone I hope you are having a good day. I had three questions that correspond to the 3 sections of the schematic shown below.

Question 1.) There is a piezoelectric buzzer that is shown below that gets connected to a microcontroller through resistors R9 and R10.

Here is the part:

http://www.digikey.com/product-s...

Usually on a beeper I would just apply power and the device would make a sound. Here is looks they are driving each end of the buzzer separately. Would it be possible to just ground one side and toggle power to the other side? Thanks for any thoughts on this.


Question 2.) Here I am not seeing how Q2.A is effecting Q14.B. To me it seems the path from the 5.0V rail to R12 to R46 is independent of Q2.A how it is currently shown.


Question 3.)

A.) This section here is supposed to be the "LED Drive" driving some LEDs.. If you look at Q3.B when this gets turned on all this does is pull the 5.0V through the 270 ohm resistor to ground. What am I missing here? This seems to serve no purpose.

B.) If you then take a look at Q3.A this FET also seems to serve no purpose. The 5.0V to R17 then goes directly to R59 and R60. These connections then go out to the LEDs. There is no path to ground through the FET Q3.A.. Just trying to do a sanity check here.



http://i1228.photobucket.com/albums/ee460/MrBlueCalifornia/Buzze_Test_LED_Drive_zpswgj67j9w.jpg

You might need to zoom in on the image.

Thanks.

-Bob

 

[Phil Hobbs]

On 05/17/2016 11:16 AM, electronicsman2016@gmail.com wrote:

Hello everyone I hope you are having a good day. I had three
questions that correspond to the 3 sections of the schematic shown
below.

Question 1.) There is a piezoelectric buzzer that is shown below
that gets connected to a microcontroller through resistors R9 and
R10.

Here is the part:

http://www.digikey.com/product-s...

Incomplete link.

Usually on a beeper I would just apply power and the device would
make a sound. Here is looks they are driving each end of the buzzer
separately. Would it be possible to just ground one side and toggle
power to the other side? Thanks for any thoughts on this.


Question 2.) Here I am not seeing how Q2.A is effecting Q14.B. To me
it seems the path from the 5.0V rail to R12 to R46 is independent of
Q2.A how it is currently shown.

It's a poorly drawn schematic, which makes it confusing. When Q2A turns
on, it pulls the junction of R12 and R46 to ground, which turns on Q14B.
R46 is there to limit the base current of Q14B, which would otherwise
be very large.

Question 3.)

A.) This section here is supposed to be the "LED Drive" driving some
LEDs. If you look at Q3.B when this gets turned on all this does
is pull the 5.0V through the 270 ohm resistor to ground. What am I
missing here? This seems to serve no purpose.

B.) If you then take a look at Q3.A this FET also seems to serve no
purpose. The 5.0V to R17 then goes directly to R59 and R60. These
connections then go out to the LEDs. There is no path to ground
through the FET Q3.A. Just trying to do a sanity check here.

All of these snippets have wires that go noplace--they look to have been
snipped out of a larger schematic. Don't waste a lot of time on it.

BTW if you crosspost using a real newsreader, folks won't have to read
the same post on multiple groups. This is definitely more of a
sci.electronics.basics post, so I'm crossposting this reply and setting
follow-ups to SEB. That's the canonical method of getting more eyeballs
on something when you're not quite sure where it belongs. That avoids
duplication and shows consideration.

http://i1228.photobucket.com/albums/ee460/MrBlueCalifornia/Buzze_Test_LED_Drive_zpswgj67j9w.jpg

You might need to zoom in on the image.

Thanks.

-Bob

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Tim Wescott]

On Tue, 17 May 2016 08:16:26 -0700, electronicsman2016 wrote:

Hello everyone I hope you are having a good day. I had three questions
that correspond to the 3 sections of the schematic shown below.

Question 1.) There is a piezoelectric buzzer that is shown below that
gets connected to a microcontroller through resistors R9 and R10.

Here is the part:

http://www.digikey.com/product-s...

Usually on a beeper I would just apply power and the device would make a
sound. Here is looks they are driving each end of the buzzer separately.
Would it be possible to just ground one side and toggle power to the
other side? Thanks for any thoughts on this.

I can't get photobucket to behave -- they seem more interested in being
click-bait than letting me look at the pictures.

There's two popular kinds of piezoelectric beepers: passive and
integrated. The passive ones are just the piezo element, possibly in a
housing, that need to be driven externally. That's probably what you
have. The active ones are basically a passive piezo element integrated
with an oscillator -- those are the ones that just beep when you apply
power.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

 

[ehsjr]

On 5/17/2016 11:16 AM, electronicsman2016@gmail.com wrote:

Hello everyone I hope you are having a good day. I had three questions that correspond to the 3 sections of the schematic shown below.

Question 1.) There is a piezoelectric buzzer that is shown below that gets connected to a microcontroller through resistors R9 and R10.

Here is the part:

http://www.digikey.com/product-s...

Usually on a beeper I would just apply power and the device would make a sound. Here is looks they are driving each end of the buzzer separately. Would it be possible to just ground one side and toggle power to the other side? Thanks for any thoughts on this.

Some piezo beepers require an oscillating signal to drive
them, others have an oscillator built in, as Tim mentioned.
If by "toggle" you mean provide an oscillating signal from
0 to 5 V fast enough, then yes, you could ground one side
and "toggle" the other to get it to beep. You'd be better
off to think of it as Tim described.

Question 2.) Here I am not seeing how Q2.A is effecting Q14.B. To me it seems the path from the 5.0V rail to R12 to R46 is independent of Q2.A how it is currently shown.

As Phil said, turning on Q2 ground the junction of R12 and R46.
R46 brings the base of the PNP (Q14) to ground. The 10K ohms
resistance limits the current into the base of Q14, protecting it,
as Phil mentioned. That turns Q14 on, which switches the voltage
at PTEST from ground to +5.

Question 3.)

A.) This section here is supposed to be the "LED Drive" driving some LEDs. If you look at Q3.B when this gets turned on all this does is pull the 5.0V through the 270 ohm resistor to ground. What am I missing here? This seems to serve no purpose.

It looks like you are missing part of the schematic. As you noted, per
the schematic, Q3B does nothing but draw current through R270 for
no apparent purpose.

B.) If you then take a look at Q3.A this FET also seems to serve no purpose. The 5.0V to R17 then goes directly to R59 and R60. These connections then go out to the LEDs. There is no path to ground through the FET Q3.A. Just trying to do a sanity check here.

Q3A does have a path to ground - pin 1 is connected to DGND.
Without seeing the LED wiring, can't tell if turning Q3.A on
will turn the LEDs on or turn them off.

Ed

http://i1228.photobucket.com/albums/ee460/MrBlueCalifornia/Buzze_Test_LED_Drive_zpswgj67j9w.jpg

You might need to zoom in on the image.

Thanks.

-Bob

 

[Jasen Betts]

On 2016-05-17, electronicsman2016@gmail.com <electronicsman2016@gmail.com> wrote:

Hello everyone I hope you are having a good day. I had three questions that correspond to the 3 sections of the schematic shown below.

Question 1.) There is a piezoelectric buzzer that is shown below that gets connected to a microcontroller through resistors R9 and R10.

Here is the part:

http://www.digikey.com/product-s...

Usually on a beeper I would just apply power and the device would
make a sound. Here is looks they are driving each end of the buzzer
separately. Would it be possible to just ground one side and toggle
power to the other side? Thanks for any thoughts on this.

it's not a beeper, it's a loudspeaker, they need a continuous wave to
produce continuous sound.

no, toggling won't work with a piezo speaker, but connecting to power
and ground alternatively will, or if you put a resistor or inductor in
parallel...



--
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