Ten second Automatic Light PIR Motion Sensor with 555 Timer in Monostable mode

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14:00:39

My personal design for an Automatic Light with PIR Motion Sensor. 

Replace the "Push Button" with PIR in real build. The PIR signal will send 3volt signal high when it detect human movement which is simulated by pressing the "Push Button". 

The 3volt signal will trigger the transistor (I'll plan to use TIP120 Darlington Transistor) and will activate the 555 Timer in Monostable mode.

The LED will light up in roughly 10 seconds. You can adjust the length of LED illumination by experimenting with the 100nF capacitor value.

The only thing that i'm concerned of is the 555 circuit take up so much current in idle mode (2.80mA) which is inefficient for low power operation IMHO.

published 6 years ago

tonyinselby

6 years ago

The simulator is simulating something like an LM555, a BJT-based 555. If you build this for real, try a CMOS-based 555, such as an LMC555. The datasheet for this states a maximum supply current of 400μA. You may need to add a driver transistor on the output, though, as it can supply a maximum of 100mA.

tonyinselby

6 years ago

Another couple of comments: If your PIR supplies a reasonable current in "on" state, I can't see the point in using a power Darlington. A cheap general purpose PNP like a 2N2906 should serve. Also, consider making the monostable retriggerable. Otherwise your light will blink annoyingly off every 10 seconds if the PIR stays "active" for a longer period than that.

tonyinselby

6 years ago

Oops. I meant general purpose NPN, such as a 2N2222. (Igor, how about making comments editable?)

mypapit

6 years ago

@tonyinselby ahh, i thought about replacing it with 2N2222 transistor. btw thanks about suggestion on making the monostable retriggable, haven't thought about that :-)

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