I am building test rigs and need to trigger motion detectors remotely. I would also like to avoid using a light source. The devices I've encountered all use an Excelitas 968 pyroelectric sensor (http://www.excelitas.com/downloads/LHi%20968%20PYD%201398%20-%20High-End%20Pyro.pdf); I'd like to remove it and use simulate its signal instead. But I've struggled to find out what I'd need to do, right down to what signal the sensor itself produces.

How can I simulate this pyroelectric sensor?

  • \$\begingroup\$ Instead of removing the sensors, what about setting up a heat source and moving it across the view of the motion detectors? \$\endgroup\$ – Bort Jan 16 '18 at 13:50

Try a voltage of about 1V and blip it up or down by say 500mV for a second or so.

You can do this with a 74HC123 or a 555 and a few resistors.

That may or may not reliably trigger the downstream circuit. PIR sensors are normally paired with a Fresnel lens that causes an AC signal from motion and you may have to do more to stimulate it, depending on how immune to curtains moving etc. they have tried to make it.

The cheap circuits just use a 5 cent LM324 quad op-amp and a few passive parts, no micro. Possibly that's what you have. The datasheet shows a sensitivity quite typical of consumer Chinese PIR sensors used in motion detector lamps etc. (3300V/W)

You might want to create a more general purpose circuit with an Arduino and PWM and play with real sensors and an oscilloscope to simulate them.

  • \$\begingroup\$ that might simulate an intruder with a blow torch (lol) \$\endgroup\$ – Sunnyskyguy EE75 Dec 9 '17 at 2:17

I calculate the FET sensitivity of this device with Drain source resistors to bias into 47 kohm source follower to gnd with low noise OA with a gain of 250 you need to detect a signal just above the white noise level around 1mV sensitivity detection needed for human size at 1m moving for x seconds. (ballpark est.)

Due to the poor specs, I would not recommend this part as a Far IR detector FET or PIR as they are called.

Instead look elsewhere. I might recommend the Zilog part for price / performance ratio and a digital output.

What are your threshold limits for size of target, range and time to detect?

These particular PIR chips are not that sensitive far away and require exceptional high gain, low noise amps.

  • \$\begingroup\$ Unfortunately, I don’t select them. The devices carry these sensors and I need to replicate their signal to trigger the device. \$\endgroup\$ – steve Dec 9 '17 at 9:43

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