laser alarm

[patrickabella851]

Works by sensing the light from the laser hitting the photoresistor which lowers the resistance, once the beam is broken the
Resistance increases and the 741 chip senses that the resistance is now higher than the 1k resistor. This results in the chip sending a
Pulse to the 4017, which sets off the buzzer and turns off the power to the photo-resistor so the buzzer will not stop when the beam is
Back on the sensor. To reset the circuit the laser must be back on the photo-resistor while you push the reset button.



please help... its seems not working......

 

[BioniC187]

What exactly is not working?

 

[Joe G]

give this a read through.

**broken link removed**

 

[patrickabella851]

i tried to simulate this circuit diagram to CIRCUIT WIZARD application the buzer did not go on... seems there is some components lacking... i need ur expertise plz...

 

[patrickabella851]

I think one resistor is missing that should be used to reduce the voltage on 741 OP Amp’s + input pin 3 to ground. Power source pin to IC 4017 and its connection is not shown. Output pin 4 of 4017 is wired OR with reset switch to Battery directly and this will discharge Battery quickly during reset. I think, this circuit is to be corrected by some expert editor and all such designs are to be reviewed before placing on the web...... can any one re construct the circuit plzz.. its our project in school..

 

[Joe G]

That is why I posted that link, its very descriptive, the missing resistor would be the other half of your "ref voltage divider". just a pot would work fine for your circuit, but give that link a read, a similar circuit is in there. it will be well worth a couple minutes of your time, you'll learn alot

 

[patrickabella851]

https://www.circuitstoday.com/super-sensitive-intruder-alarm... another laser alarm circuit is working jus need a reset button .... thanks guys!!