Hi y'all

I'm putting together a PIR sensor circuit that will trigger a 555 timer in monostable and run a set of LEDS for about 5 sec all on a 3v cr2032 button cell battery and than reset until next motion is detected.

The PIR module I have is a 8845 module from TI that is specifically built for low voltage applications down to 1.8 V.

The timer is the TI LMC555 good down to 1.8 V as well.

Im trying to do it all on one button cell but have run into a re triggering issue where the PIR module re fires continuously one 5 sec cycle after another. I can make out a brief glimmer in between each cycle.

The timer and pir module both act great when not connected to one another.

When PIR Module has its own supply(another 3v) with common ground and the 555 and LEDS have the other 3V supply the system works good.

When the PIR module and 555 share positive supply and the LEDs has its own supply it has the same triggering problem.

This makes me think I have a problem with the way my 555 timer is setup. I have experimented what seems like endlessly and just can't seem to get it to work and like I said things work great separately until the 555 and PIR share the same power supply.

Any solutions?

S1 = PIR Module

EDIT: When I run the circuit with two 3V in series I still get the same problem so don't think it is a low voltage problem.

  • \$\begingroup\$ Your schematic can't work. There are no base resistors for the BJT's and current limiting for the LEDs. You also cannot drive LEDs at 1.8V or less without special drivers. \$\endgroup\$ – Jack Creasey Aug 27 '18 at 3:32
  • \$\begingroup\$ @JackCreasey Sure it will work. Then one or the other will get hot and go poof. Maybe it will take several minutes, maybe not. \$\endgroup\$ – user253751 Aug 27 '18 at 3:46
  • \$\begingroup\$ @immibis Then you seem to have a different definition of a circuit that will 'work'. which I would not necessarily use, and would not recommend to others. . \$\endgroup\$ – Jack Creasey Aug 27 '18 at 14:21
  • \$\begingroup\$ @JackCreasey I think it's important to elaborate on what is meant by "not work". Because otherwise Brendan is likely to plug it in, see that the LED lights up when it should, and think you're a liar. \$\endgroup\$ – user253751 Aug 27 '18 at 22:10

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