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Basic Electronics » PIR motion sensor to trigger home wireless camera problems

March 23, 2012
by victor
victor's Avatar

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!

March 23, 2012
by 6ofhalfdozen
6ofhalfdozen's Avatar

Hiya Victor,

I have read both your posts and the datasheets a couple times and I am stumped. Something is wrong, but not sure what.. A couple things did come up that might help track down the issue. hopefully you have a good multimeter!

A. What is the jumper setting on the PIR? Hi or Lo? If it is Hi, does setting it to Lo fix the problem? (datasheet says in Hi mode can send constant 5V if repeatedly triggering, where as Lo will send 0v-5v-0v pulses even then constantly triggering)

B. What are the voltages across your grounds? So what is the voltage across the camera input ground and the breadboard ground?? Ideally from camera input ground to breadboard ground should be a very nice steady 0v, but if they are off, that could play havoc with the sensor/inputs. Also, if you can tell, what is the voltage from the camera power's ground to the breadboard ground?

C. When you jumpered the 1K resistor from camera input to ground: which ground? camera input ground (ie pin 3 to 4?) or camera input to breadboard ground? Also, when you did this what was the state of the PIR? (and to check the state of the PIR while testing, you can wire a parallel indicator for the PIR that goes from PIR output to LED to >500 ohm resistor to breadboard ground, this will tell you when PIR is indicating person, without pulling too much power as to not let the camera see the output too.. the LED will be dim..)

C. The pins for the camera seem really wierd. Have you check the voltages across the various pins on the input to the camera? (ie 1 to 2, 2 to 3, 3 to 4, and so on?? ) While the camera looks pretty pricey, the pinouts seem kinda odd. It makes me wonder if the manual was translated from some other language and might be worded somewhat misleadingly. Obviously this is a long shot and if you do any testing of that you will need to be super carefull as swapping what signals go where can be a good way to kill nice electronics.

D. What is the "motion detect sensitivity" on the camera set to?? Is it possible this is too high or too low??

E. Any chance you could post a picture or two of your setup/wiring? there might be something the eye can see that words have a hard time getting.

just some thoughts, hopefully helpful.

March 23, 2012
by victor
victor's Avatar

6ofhalfdozen , Thanks a lot! I ground my camera and PIR together so they should be the same. It was in the first post but the formating was messed up. here it is:

PIR CAMERA

GND -- GND

VCC -- the PIR DC power

OUT -- INPUT

March 23, 2012
by 6ofhalfdozen
6ofhalfdozen's Avatar

Victor,

I am still a little confused on your wiring. I am a little slow today, sorry. I will blame it on all the heat in March when it should be cold and good for thinking.

Anyhow, when you said "the PIR DC Power" under the camera column, does that mean you are using the VCC to power the PIR on the + pin and then jumpering from that pin to the Camera DC Power input on the barrel socket? or was that a typo and should read "camera dc power". If you are not using the barrel plug to connect to the camera, is it possible you are touching the ground portion of the socket with the 5VDC and leaving everything at 5Vdc? (i think ground is the outside ring not the pin on the camera power socket, it's hard to see in the datasheet)

stumped again, but something else to think about...

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