Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Please help modified a circuit

Status
Not open for further replies.
I did everything that you said but still the buzzer wont stop

please see this

is this the capacitor that I have to use ? the one of 47nF

it's writting on it

473
 

Attachments

  • Image330.jpg
    Image330.jpg
    2.5 KB · Views: 135
A fuzzy photo without any light is useless.
A capacitor marked 473 is 47nF.

Disconnect everything from pin 2 of the 555 except the 10k resisitor to the positive supply, the 47nF capacitor and the other 10k resistor to the positive supply at the other end of the capacitor. Ground the input for a moment like this:

The 555 should get triggered, the buzzer should sound for the timing then stop when the 555 times out.

Please stay in only one website's forum.
 

Attachments

  • 555 monostable timer.PNG
    555 monostable timer.PNG
    10.8 KB · Views: 140
I done the circuit
and I touched the * to the ground then the buzzer made sound
but didn't stop

there was no timeout for 555
 
cannibal said:
I done the circuit
there was no timeout for 555
Then either the 555 is defective, or the leakage current of C2 is too high or the value of R7 is too high.

If all your questions were on a single website then i could see the values of C2 and R7.

What is the voltage of the battery? Maybe its voltage drops too low when the buzzer is activated.
 
Replace C2 because it might have too much leakage current then it will never fully charge. Make certain it isn't connected with backwards polarity.

The minimum operating voltage for a 555 is 4.5v and yours might drop lower when the buzzer is activated. So try a 6V or 9V battery.
 
I replaced the C2 with new one (10uF)
the polarity connection checked correct

battrey changed to 9V

the problem still
buzzer won't stop when it get activated :(
 
cannibal said:
I replaced the C2 with new one (10uF)
the polarity connection checked correct

battrey changed to 9V

the problem still
buzzer won't stop when it get activated :(
Maybe the 1M pot doesn't conduct.
Replace the defective 555 IC.
 
audioguru said:
Maybe the 1M pot doesn't conduct.
Replace the defective 555 IC.

Hello

Just want to make sure before buying new 555 IC

after how many seconds the 555IC should time out ??

because I waited for 2 minutes and no time out
 
cannibal said:
after how many seconds the 555 IC should time out ??
Why ask? Simply look on the datasheet.

1.1 x 10uF x 1M= 11 seconds with the pot at max resistance. They show a graph that looks like 8 seconds.
The 10uF capacitor could be actually only 8uF or 12uF and the 1M pot could be only 800k or 1.2M so the time will be somewhere from 7 seconds max to 16 seconds max.

Since you replaced the capacitor and made certain its polarity is correct then either the 555 is bad or the pot doesn't conduct.

Before buying another 555 try a 1M resistor to replace the pot.
 
Measure the output voltage at pin 3 of the 555. With a 9V supply it will go high to about +7.5V to turn on the transistor that drives the buzzer.
Then after about 12 seconds its output will go low to about 0.1V which turns off the transistor.

Maybe the transistor is wired incorrectly or is shorted.
 
the output voltage at pin 3 with 9V supply is +7.7V
after 12 seconds it's same +7.7V
after more then 2 minutes it's same +7.7V


well I am using BC337 transistor
I wired it like the picture
 

Attachments

  • ttssioer.GIF
    ttssioer.GIF
    1.9 KB · Views: 137
Your transistor's pins are correct.
Didn't you solder the circuit together? Or is it on a breadboard that has intermittent contacts?
Make sure that pin 6 of the 555 is connected to the 10uF capacitor and 1M resistor.
Make sure that the 1M resistor connects to the positive supply.

What kind of buzzer? A mechanical one has a coil that creates high voltage spikes that needs a diode across it to stop the spikes from destroying parts in the circuit.

Did you wire the circuit exactly like this?
 

Attachments

  • 555 monostable timer.PNG
    555 monostable timer.PNG
    11.9 KB · Views: 233
I am using breadboard

and yes I connect like you show in the picture but the same problem



my friend told me that he made same circuit but less complex and it worked with him

so I took his idea and I connected to the breadboard like the following picture

but still the buzzer won't stop when it's activated


I also attached a picture of the buzzers that I am using
 

Attachments

  • CA4TAJS111x.GIF
    CA4TAJS111x.GIF
    4.9 KB · Views: 164
  • bblinks.gif
    bblinks.gif
    9.7 KB · Views: 127
  • picbuzzermytww.jpg
    picbuzzermytww.jpg
    4.2 KB · Views: 131
The new circuit you attached has the transistor connecting pin 2 of the 555 to ground when it is dark. The 555 does not time out when its pin 2 is low.

That is why I added a resistor to make pin 2 high and a coupling capacitor to pulse pin 2 low for a moment.

You forgot to join pin 6 with pin 7.

Post a pic of my circuit on the breadboad.

The left buzzer is a piezo beeper. I don't know what is inside the right one.
 
Finaly the circuit is working just fine the buzzer fixed :)


the problem was





I forgot to connect pin 6 to pin 7 :D

very big thanks to you Mr. audioguru

thanks for your time ;)
 
Last edited:
One more additional question

how to add extra photoresistor in this circuit


so if one of them is in drak mode then the buzzer will be activated even if the other pototransistor is in light mode
 

Attachments

  • CA4TAJS111x.GIF
    CA4TAJS111x.GIF
    4.9 KB · Views: 146
cannibal said:
One more additional question

how to add extra photoresistor in this circuit


so if one of them is in drak mode then the buzzer will be activated even if the other pototransistor is in light mode
Connect another transistor, LDR and 100k pot in the same manner as is shown in the diagram and connect the collector of the second transistor to the collector of the first.

Thus if one or the other LDR is in the dark, the associated transistor will be turned on.

By the way, I notice that you now have the buzzer connected to the 555 output without Q3 - as I suggest previously.
 
Good, I am glad you fixed it.

I don't think the new circuit will time out when it gets dark. The datasheet for the 555 says that pin 2 must be high for it to time out. The transistor holds pin 2 low when it is dark.

I think a coupling capacitor and resistor are needed at pin 2 like this:
 

Attachments

  • 555 timer.PNG
    555 timer.PNG
    9.1 KB · Views: 276
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top