I'm developing a small home security project using Nerdkits, so far using it as 5v power DC supply but later will put more logics into the MCU.

I tried to use a PIR motion sensor to trigger my home wireless camera, thru the camera "Armed Input", their models are: PIR http://www.parallax.com/Store/Sensors/ObjectDetection/tabid/176

wireless cam http://www.scribd.com/doc/29523918/Foscam-us-FI8908W-manual

"Alarm Input Armed Input Pins: The input pins can be used for 1-way external sensor input. For example, you mayconnect a Person Infrared Sensor (PIR) to it for motion detection. When external sensor triggered,IPCAM can be programmed to send an email with picture or control the internal relay output.If you link a external alarm with Pin3 and Pin4,when enable alarm input armed,external alarm is enabled."

According to this, I connected PIR and camera like this:

PIR CAMERA GND -- GND VCC -- the PIR DC power OUT -- INPUT

1), PIR has been tested separately and works perfectly, say, when idle, out and gnd is 0v; when motion, out and gnd is 5v.

2), but the weird thing is: when i measure the camera input and gnd， it is always 5V ？！ Be more precisely, when PIR idle, it's 4.8v, when PIR motion triggered, it's 4.2v...

3) next, i used a 1k ohm resister to short the camera input and gnd. once it's shorted, the camera is triggered. (i can get an email)

i guess it's something wrong with the TTL voltage etc, but without knowing the camera circuit design, i've no clue how to fix it....

thanks!

The PIR sensor has a jumper wire under it. You probably have it on low trigger mode. See if you can change it.