Branching off this thread from five years ago:
https://forum.allaboutcircuits.com/threads/motion-sensor-555-timer-project.91536/

I have a similar need, but I'm using a Radio Shack 273-0071 12V 40mA chime. I'd like the 555 to chime it for a couple of seconds and then 'shut up' for a while if motion is still detected. I'm using the same three pin PIR sensor as in the previous thread. Note that the 273-0071 has three wires - plus, minus, and "contact" (blue). + and - stay powered all the time. When "contact" is grounded, it chimes for two cycles (ding dong, ding dong.) If contact is still grounded after those two cycles, it'll chime again. So, even momentary contact would be nice for the chime to "ding dong" twice.

Can someone help me make modifications to the above linked circuit based on the new requirements? I'm aware this is pretty simple, but I've never used a 555 before, and the data sheet just makes me ask even more questions about values, etc.

Thanks!

 

Welcome to AAC!

The formula for a one shot is 1.1RC. Or you can use this graph:

(There's a typo on the graph. It should only give Ra.)

200k ohm and 10uF will give a nominal 2.2 seconds, but component tolerances need to be considered.

Is the output from the sensor a pulse? If it stays low as long as motion is detected, you'll need to AC couple to the trigger input and put a pull-up resistor on the trigger input side.

Like this:

 

Please post a link to the PIR sensor you want to use. Also, what is the power supply voltage for your application? My guess is that the PIR output rests low, and goes high (but only to 3.3 V) when triggered by something. If so, that is the wrong direction to trigger a 555. But an intermediate transistor might be necessary anyway if the 555 power is 9 V or 12 V, as 3.3 V won't be high enough to trigger it.

ak