Hello all,
Am new here and I was impressed the way people interact and help each other here.
I was making a project based on PIR motion sensor.
The circuit works as the motion sensor senses the motion, it gives output (3.3V) to the 555 timer (Pin 2) which i have used in Monostable mode.
Now the output of this 555 timer (Pin 3) is connected to the relay in such a way that as the o/p gets low, a lamp turn ON through relay.

This circuit works fine <ON BREADBOARD> and as i have expected

Now when i made this made the same circuit on a PCB it doesnt function as in breadboard. And frankly, i have checked it about 10 times and i found no mistake or shorting in the Souldering.

ISSUE is:
Whenever the Motion sensor triggers the timer (Pin 2), Pin 3 should go low. But it isnt going low. I need help.......

 

What is your supply voltage to the 555? A standard 555 is marginal in its operation even at a Vcc of 5V. How does a 3.3V pulse trigger a 555 that is running on 5V? Post a schematic...

 

Actually My supply voltage to 555 timer is 5V DC. The triggering voltage needed for 555 timer is 1.67 V. Thats why i managed to give 1.7V to the i/p (Pin2) by adding resistors between o/p of the sensor and i/p of 555.
The schematic is attached.

 

Your circuit is wrong, you need to feed a 0v trigger to pin 2, then the timer will go high for the set period, then it will go low, if pin 2 is kept low for longer than the time pulse, pin 3 will stay high permanent,

if your pir gives out a positive pulse, you need a Npn transistor to invert the pulse to make it work.

 

If your PIR put out a logic signal that swings from 0V to 5V, it would be this easy:



Note that the AdaFruit PIR has an internal jumper to make the output signal either 3.3V or 5V.

If yours is not strap-able, then you will need a level-shifter to convert the 3.3V signal to a 5V one. Like this:



Are you sure that your PIR sensor doesn't have an open-collector output?

 

Model of my PIR sensor is DYP-ME003.
I am giving it a Vcc of 5V and it's default output is 3.3V (when motion is sensed).
Now am giving this o/p voltage to pin 2 of 555 timer.
This time instead of giving the o/p directly to the timer circuit, I have given it through a NPN transistor (BC547). As suggested by Dodgydave to give inverted i/p as to get fruitful o/p.
The problem now arised was, whenever there's a trigger, the o/p gets low making my Lamp turn OFF. That's why i used another inverter at the i/p of the relay and it works fine. <again only on breadboard>

 

If you invert the input, there is no need to invert the output:

 

Ohh yes @MikeML I recognized that yesterday and that was so helpful ... Impressed by the way you explain stuff. Thanks for that
And Which circuit simulator do you use?

 

Ohh yes @MikeML I recognized that yesterday and that was so helpful ... Impressed by the way you explain stuff. Thanks for that
And Which circuit simulator do you use?

LTSpice. free download at linear.com