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On Thu, 16 May 2019 07:17:26 -0700 (PDT), AK
<scientist77017@gmail.com> wrote:
No, a field effect transistor will switch with almost no current into
the gate, so their main advantage in switching applications is that
they don't load down the driver circuitry.
They have very high impedance inputs. They can be destroyed by static
electricity, so the gate shouldn't be allowed to "float," and there's
some limitations on the gate that are in the data sheet for the part
you are using. The maximum gate voltage for a lot of FETs is on the
order of ~10 volts.
A junction transistor is probably fine for your application. They are
somewhat more rugged. But unlike FETs they need current limiting into
the base or they will overload the 555 or be destroyed themselves. For
what you are doing, 1,000 ohms to 5,000 ohms is probably going to
work.
Normally you'd calculate what you need based on the gain (Beta) of the
transistor. Gain of 100 and that means the base needs 1/100 of the
current that the load will impose on the collector - but look at the
graphs, since gains are usually stated as minimum/typical/maximum for
the part, and they change with temperature, and the amount of load. If
you want to calculate it, but you shouldn't need a driver unless the
buzzer has a problem.
What kind of buzzer is this anyway? A piezo buzzer doesn't need a lot
of power, something like an electromechanical buzzer would draw a lot
of current and a 555 probably couldn't drive it directly. Unless it
is a bad buzzer (shorted).
A typical piezo buzzer uses from 5-100 milliamps depending on the
part, and the 555 should be able to source that with no problem.
from
https://electronicsclub.info/555timer.htm
The output of a standard 555 can sink and source current. This means
that two devices can be connected to the output so that one is on when
the output is low and the other is on when the output is high, the
diagram shows two LEDs connected in this way.
The maximum output current is 200mA, this is more than most ICs and it
is sufficient to supply many output transducers directly including
LEDs (with a resistor in series), low current lamps, piezo
transducers, loudspeakers (with a capacitor in series), relay coils
(with diode protection) and some small motors (with diode protection).
The output voltage does not quite reach 0V and +Vs, especially if a
large current is flowing.
To switch larger currents you can connect a transistor.
NOTE!!!
The maximum output current of low power versions of the 555 (such the
ICM7555) is much lower: about 20mA with a 9V supply.
<scientist77017@gmail.com> wrote:
On Thursday, May 16, 2019 at 8:37:23 AM UTC-5, George Herold wrote:
On Wednesday, May 15, 2019 at 5:31:32 PM UTC-4, AK wrote:
On Wednesday, May 15, 2019 at 2:46:05 PM UTC-5, Rodney Pont wrote:
On Mon, 13 May 2019 19:22:56 -0700 (PDT), AK wrote:
Electronic can be quite frustrating.
I put together a circuit for a laser alarm.
It does not work.
There is no way to tell if a design will be successful even if you follow the authors exact directions.
I will keep plugging away and reading Practical Electronics for Inventors.
Can you post a picture of the assembly so that someone can check that
you have understood how to put the circuit together?
--
Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail rpont (at) gmail (dot) com
https://www.dropbox.com/s/leak8ty4dsmw88e/Project2.jpg?dl=0
https://www.dropbox.com/s/edy9xs8p5rfm15q/Project1.jpg?dl=0
The ne555p chip got fried. I got 0 volts at pins 3 and 6.
I have one left.
If someone can step me thru this, I will risk my last chip.
Andy
Hmm, I'm too lazy to check the wires... (and don't know the 555)
How about some capacitance (0.1uF) across the supply rail.
Maybe put some resistance in the power input to limit current..
~ 100 ohms?
How much current does the beeper draw when it's on?
Here's something done with a comparator or opamp.
https://www.dropbox.com/s/gobqe2a4mfqvbuu/light-sens.JPG?dl=0
(the lower circuit scribble)
Comparator could be LM339 or similar.. but then needs a pull up resistor on
the open collector output.
George H.
I believe I have the circuit working. I had to replace the piezo buzzer with a led.
It now lights up in ambient light and turns off when I shine a laser on it.
I read that I need a field effect transistor in order to drive a buzzer.
Is that true?
Andy
No, a field effect transistor will switch with almost no current into
the gate, so their main advantage in switching applications is that
they don't load down the driver circuitry.
They have very high impedance inputs. They can be destroyed by static
electricity, so the gate shouldn't be allowed to "float," and there's
some limitations on the gate that are in the data sheet for the part
you are using. The maximum gate voltage for a lot of FETs is on the
order of ~10 volts.
A junction transistor is probably fine for your application. They are
somewhat more rugged. But unlike FETs they need current limiting into
the base or they will overload the 555 or be destroyed themselves. For
what you are doing, 1,000 ohms to 5,000 ohms is probably going to
work.
Normally you'd calculate what you need based on the gain (Beta) of the
transistor. Gain of 100 and that means the base needs 1/100 of the
current that the load will impose on the collector - but look at the
graphs, since gains are usually stated as minimum/typical/maximum for
the part, and they change with temperature, and the amount of load. If
you want to calculate it, but you shouldn't need a driver unless the
buzzer has a problem.
What kind of buzzer is this anyway? A piezo buzzer doesn't need a lot
of power, something like an electromechanical buzzer would draw a lot
of current and a 555 probably couldn't drive it directly. Unless it
is a bad buzzer (shorted).
A typical piezo buzzer uses from 5-100 milliamps depending on the
part, and the 555 should be able to source that with no problem.
from
https://electronicsclub.info/555timer.htm
The output of a standard 555 can sink and source current. This means
that two devices can be connected to the output so that one is on when
the output is low and the other is on when the output is high, the
diagram shows two LEDs connected in this way.
The maximum output current is 200mA, this is more than most ICs and it
is sufficient to supply many output transducers directly including
LEDs (with a resistor in series), low current lamps, piezo
transducers, loudspeakers (with a capacitor in series), relay coils
(with diode protection) and some small motors (with diode protection).
The output voltage does not quite reach 0V and +Vs, especially if a
large current is flowing.
To switch larger currents you can connect a transistor.
NOTE!!!
The maximum output current of low power versions of the 555 (such the
ICM7555) is much lower: about 20mA with a 9V supply.