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circuit breaker alarm

Alistair Ballantyne

Nov 16, 2020
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Hi, I'm keen to make a simple circuit beaker alarm and thought the following layout ideal.
Although the site (electronics hub) shows the buzzer sounding when the beam is broken I just cant get it to work.
When powered up the buzzer just sounds consistently.
No idea what I am doing wrong.
Any help and guidance appreciated.
Thank you.
1711471631916.png
 

bertus

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Nov 8, 2019
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Hello,

Wich opamp are you using?
Wich buzzer are you using?

It can be that the buzzer broke the opamp.

Bertus
 

Alistair Ballantyne

Nov 16, 2020
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Hello,

Wich opamp are you using?
Wich buzzer are you using?

It can be that the buzzer broke the opamp.

Bertus
Sorry should have specified - LM358 and simple 90db buzzer.
The circuit calls for a 5v source which I made using a simple 7805 conversion.
But makes no difference 5v or 9v.
Why would the buzzer break the op amp?
Should I remake the circuit with a new LM385 and replace the buzzer with an LED?
 

bertus

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Hello,

How much current does the buzzer take?
Are there specifications of the buzzer?
If the current of the buzzer is to high, the opamp may break.

Bertus
 

AnalogKid

Jun 10, 2015
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First guess, the photodiode is not passing enough current to pull up the non0inverting input above the pot setpoint.

Pin 5 is low >> pin 7 is low >> buzzer is on.

Link to the original circuit page - ?

ak
 

Alistair Ballantyne

Nov 16, 2020
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Hello,

How much current does the buzzer take?
Are there specifications of the buzzer?
If the current of the buzzer is to high, the opamp may break.

Bertus
I'm afraid I have no idea of current consumption.
Ill try a new 385 with an LED without buzzer and see how that goes.
 

Harald Kapp

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At 5 V supply, the max. output High voltage of the LM358 is ~ 3.5 V:
1711474218500.png
That means the buzzer is supplied by ~1.5 V (5 V supply - 3.5 V output of the opamp). That may be enough to make it buzzzzzzzzzzzzzzz.
You could
  1. use another opamp with rail-to-rail output that goes all the way up to 5 V.
  2. use a zener diode in series between the opamp and the buzzer. Something around 1.6 V or so. Additionally use a resistor in parallel to the buzzer , [imath]1 k\Omega[/imath] or so. The absolute value is not critial. This resistor helps to bypass the leackage current through the zener diode.
 

Alistair Ballantyne

Nov 16, 2020
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First guess, the photodiode is not passing enough current to pull up the non0inverting input above the pot setpoint.

Pin 5 is low >> pin 7 is low >> buzzer is on.

Link to the original circuit page - ?

ak
what should I do to determine that?
 

Alistair Ballantyne

Nov 16, 2020
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At 5 V supply, the max. output High voltage of the LM358 is ~ 3.5 V:
View attachment 63171
That means the buzzer is supplied by ~1.5 V (5 V supply - 3.5 V output of the opamp). That may be enough to make it buzzzzzzzzzzzzzzz.
You could
  1. use another opamp with rail-to-rail output that goes all the way up to 5 V.
  2. use a zener diode in series between the opamp and the buzzer. Something around 1.6 V or so. Additionally use a resistor in parallel to the buzzer , [imath]1 k\Omega[/imath] or so. The absolute value is not critial. This resistor helps to bypass the leackage current through the zener diode.
What op amp would you recommend?
The zener diodes I have are 4.3v. That ok?
 

Harald Kapp

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What op amp would you recommend?
Here's a selection of so called rail-to-rail (r2R) opams.

The zener diodes I have are 4.3v. That ok?
No. That is way to much. The buzzer will "see" only 700 mV when the output of the opamp is low. 300 mV are insufficient for proper operation of the buzzer.
Instead of a 1.6 V zener diode you can use 3 run-of-the-mill diodes, e.g. 1N4148, in series. These will drop +1.8 V ...2.1 V. Good enough for this application.
 

Alistair Ballantyne

Nov 16, 2020
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Alistair Ballantyne

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Great thanks!
Presume you make in two sections - transmitter and receiver?
Great thanks!
Presume you make in two sections - transmitter and receiver?
I'm despairing here - no idea what I'm doing wrong.
Built the circuit using TSUS 5400 emitter and BP41 photodiode.
Used a BC548 instead of 2N3904 but made sure pin 1 collector is connected to buzzer and pin 3 emitter connected to ground.
The buzzer just constantly sounds when powered - no beam breaking involved.
The emitter on different breadboard but pointed to the IR receiver face of the BP41.
Any thoughts please?
1711715532574.png
 

Alistair Ballantyne

Nov 16, 2020
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I like garlic bread with my spaghetti... :cool:

Here you go kiddo.
I like garlic bread with my spaghetti... :cool:

Here you go kiddo.
Well that's extremely helpful.
If I thought for one minute I was going to be formally assessed on the neatness of my wire cutting then I would have made a more strenuous effort.
However, I just wanted to create the linkage to see if the circuit worked before soldering.
If I deployed commonly used jumper wires then the "spaghetti" would be worse.
Can you clearly see which wires link to which component? I think you can despite a less than meticulous positioning on the breadboard.
Whilst we are being pedantic may I inform you that your statement "its a lot more better" is appalling English.
It is technically called tautology which the Oxford English Dictionary describes as follows:
"The use of two words or phrases that express the same meaning, in a way that is unnecessary and usually unintentional".
All I wanted to know from you experts is where I have gone wrong.
If that is the extent of your help then please don't bother.
Seriously, don't bother.
 

bertus

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Hello,

I do not see where the wiper of the potmeter is connected.

For better understanding of the layout of a breadboard, have a look at the following picture:
breadboard-connections.jpg
Also have a look at the attached PDF.

Bertus
 

Attachments

  • breadboard.pdf
    289.4 KB · Views: 1
Last edited:

Delta Prime

Jul 29, 2020
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I was just worried about excessive power connected impedance.
The inductance of the leads that couple the power supply to the operational amplifier.
it is essential to properly decouple or bypass all power-supply leads to amplifiers without internal decoupling networks. Good design practice includes using a fairly large value solid-tantalum
electrolytic capacitor from the positive and the negative power supply to ground if you're going to go rail to rail operational amplifiers.
Power supply lead length of your jumper wires on your breadboard are critical because lead length inductance will cancel out your coupling capacitors capacitance value allowing any transient voltages to damage your circuits operational amplifier.
Take a look at this circuit it's pretty much bulletproof.
photo_1711726033065.pngphoto_1711726192766.png
 

Attachments

  • Forrest Mims-Engineer's Mini-Notebook Optoelectronics Circuits (Radio Shack Electronics).pdf
    4.1 MB · Views: 2

AnalogKid

Jun 10, 2015
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The #1 schematic shows 1/2 of an LM358 for the opamp, and you mention the LM358 in other posts.

BUT . . .

The opamp in post #16 is a 741, and the wiring is correct for a 741. However, a 741 will not run correctly on 5 V. Per the datasheet, the minimum Vcc is 10 V (or +/-5 V).

The photo also shows a resistor from the inverting input to Vcc. I think I know what you are trying to do here, but the pot wiring is incorrect.

Please post a new schematic.

AND, since no one else has said it - cover the photodiode and see what happens. Probably nothing given the other circuit issues, but . . .

ak
 
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