PIR sensor project

Rleo6965

Joined Jan 23, 2012
9
The reason LM555 was not triggered was due to high output voltage near your +VCC and far from 1/3 VCC that needed to trigger the LM555 Trigger Input.

I suggest that you place resistor in series to R15 to ground. Acting as voltage divider.. You can try 10K for both R!5 and R?? that I suggest. Result trigger voltage will be 1/2 VCC near the 1/3 VCC that LM555 trigger voltage required. It's now easier for the LM358 to pull down it to below 1/3 VCC and therefore trigger LM555.

Pls try to place pullup resistor 4.7K on Output pin of LM358. It's also a open collector comparator.
 
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Thread Starter

fila

Joined Feb 14, 2011
64
The reason LM555 was not triggered was due to high output voltage near your +VCC and far from 1/3 VCC that needed to trigger the LM555 Trigger Input.

I suggest that you place resistor in series to R15 to ground. Acting as voltage divider.. You can try 10K for both R!5 and R?? that I suggest. Result trigger voltage will be 1/2 VCC near the 1/3 VCC that LM555 trigger voltage required. It's now easier for the LM358 to pull down it to below 1/3 VCC and therefore trigger LM555.

Pls try to place pullup resistor 4.7K on Output pin of LM358. It's also a open collector comparator.
Thanks for the suggestion but I am using an LM393 and it now works fine. LM358 is a dual operational amplifier, not a comparator.
 

Thread Starter

fila

Joined Feb 14, 2011
64
LM555N is causing me some major problems. I've been reading some datasheets and forums and I've learned that it (and 555's in general) creates some huge current spikes during transitions. That spikes are totally ruining my circuit operation.
I connected some bypass capacitors (22 μF electrolytic in parallel with 0.1 μF) across it's Vcc pin and GND pin but it didn't help me at all. I've reached the deadline with my project and the whole circuit is soldered. I just want to know would it help to replace the LM555 with CMOS 555.

Just for the information the project is not a complete failure. Circuit sometimes works correctly but to often it gets re-triggered because of the 555 current spike.

So in general is the CMOS 555 more effective than the standard 555 when it comes to supply current spikes and to what extent?
 
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