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How can I modify a PIR so triggers faster, and then fades out? Answered

I want to make a motion-activated light that turns on immediately when someone walks by for about a second, then fades out for about one second. Most PIRs seem to stay on for a minimum of 5 seconds, then just cut off. I'm looking for a quick burst, quick fade. I'm very new to working with electronics, but my guess would be that instead of modifying the PIR itself, the PIR would be triggering something else that would be doing the timing/fading.


Jack A Lopez

5 weeks ago

I think the answer depends on what you are using for the light.

I mean, if I follow what you are saying, you want the brightness of the light to change, in a particular way, as a function of time.

For mains powered lights, made to be dimmable,


the brightness of the light will change in response to the magnitude of the RMS voltage powering it, and the usual trick for dimming this kind of light is this funny TRIAC-based circuit (sometimes called, "phase triggered", "phase controlled", etc.) that only turns on for some fraction of the period of the AC waveform.

If the light is some big array of LEDs, then that is kind of a DC thing. I mean the way to control the brightness of that would be by changing the LED current; i.e. use a constant current regulator that can be controlled by some other signal, like an analog voltage, or a PWM signal.

Actually, that feature: control via some other signal, would be probably also be wanted in the case of an AC load as the light. I mean, you would want the lamp dimmer to be a dimmer that could be controlled by some other signal, like an analog voltage or PWM.

But where do you find a signal controlled lamp dimmer? Are those easy to find? Or is it necessary to build one?


5 weeks ago

You can get standalone PIR modules.
Just add whatever you need ;)