PiR Sensor strange behavior with radio transmissions

[razor]

Hi folks

I was trying to make a node hosting a PiR Sensor and a photocell.(to enable light on move or at night).
The node is reporting light level every 10s.
After fewhours trying to understand why a motion message was sent after each data transmission I discovered something really weird:

the PiR sensor is sensitive to 433 HW full power transmission !

MY PiR sensor is the one from Felix modded for low power.

Even when just connected to 5v and Gnd, at 20cm distance I can see thanks to the Voltmeter that the PiR is activated everytime a node packet is sent.

Motionmote is sending data only when triggered by the motion so not impacted.

Any idea on how protect the PiR from such "noise" ?

[Felix]

So what exactly is your hardware setup?
BTW this behavior was discussed in the forum in the past.

[razor]

So what exactly is your hardware setup?
BTW this behavior was discussed in the forum in the past.

A moteino RFM69HW 433 stacked on a switchmote 2x10A kit
no ATC, default power settings
nothing else as I removed the photocell to debug that.

PiR GND     ->     GND on moteino
PiR VCC     ->      VIN on moteino (5.25v from the PSU)

then to capture the PiR action:
Voltmeter on  GND and on PiR OUT

0v reading when nothing happen
5.2v for 3sec when something move
5.2v for 3sec after moteino packet sent

PiR is on 20cm cables so 20cm far from the antenna more or less.

Power to the PiR remains stable.

[razor]

same behavior when the PiR is on the 3.3v pin.

[Felix]

SwitchMote + PIR?  Interesting 
20cm cables most likely a problem, with the cheap chinese PIRs they will act like antennas. If you have the keep them so long I'd wire a 10K pulldown on the OUT of the PIR and see if that helps.
Also try ATC, it will not hurt, instead I would recommend it on any node to keep them as quiet as needed, within your chosen range.
The PIR Vcc should be at least 4v or so if you use a stock one (the regulator+diode are not removed from it).

[AcE Krystal]

I'm having same problem.
I'm making ~30 nodes, but some of the PIR's keep triggering. I already got rid of the most caused by a K30 CO2 sensor on every one of them, by adding some caps (0,01uF + 22uF). But it is still not gone. It even kept occurring while the PIR is the only thing connected to the monteino.

I have spent many hours no to find the precise cause, but I just can't find any!
- Switching PIR's, Monteino's, cables, breadboards, power adapters, with or without other sensors, with or without caps (0,01uF / 22uF, or mulltiple of the same), adding flyback diode. I tryed it all multiple times but I just can't find any patern to it.
- I did find out i can see a drop of 5,09 to 5,07V on my scope every time a 433 message is send, and that the PIR (almost) alway's triggers when a 433 message is send. But this drop is so small... it shoudn't be the main problem. a connected K30 (with the caps) has a much bigger drop on my scope but does not trigger the PIR.
Shielding?
At some point I was convinced it had to do something with the radiation that triggers the PIR electronics. Specially since the PIR seems trigger most often/alway's when placed in some specific place with clear sight to the monteino. I'm using 10CM cables. When I place the 10CM cable between the RFM69 and the PIR the PIR seems to (most often) work fine, but with direct sight to the RFM69 chip it gets triggered. So I added som alu-foil on the back of the PIR, and grounded it... but this did not help. So I got a other PIR with a different power source (not from the same breadboard) and this proved my theory wronge... the PIR with its own (same type of) power supply did not get triggered. So then it is not radiation, but really some noice? in the power lines caused by a 433 message.

I tryed a lot of things but just can't find out what is happening.
The best I can get at the moment is placing the PIR rather close the the Monteino, with the 10CM cable folded way close to the RFM69 antenna. We did this at the beginning just to stow away the cable, and somehow it gives us 2 problem modules every 6 modules we build. But it irritates me that some have this problems and some don't, while there is no explanation for it. But I get the idea that if a PIR works, it is just on the edge of working or not.

Does someone has any idea how to fix/suppress this?

Below picture of some testing. The 3rd from the front has the PIR cable under the K30 CO2 sensor alongside the RFM69 antenna, and strangely enough this gives the best results.
On the scope you see a detected 433 message drop. The PIR is connected to the 5V rail.
We also removed the Diode from the Monteino, since this dropped the voltage to much for sensors like the K30.

[WhiteHare]

From what I've read, that type of PIR modules is extremely sensitive to changes in voltage.  It's inherent in the design.  It continually looks for any small change in the voltage of the left side of the sensor element as compared to the right side of the sensor element as an indication of motion. 

[Felix]

I bet the long cables are picking up EMI like an antenna.
I don't see these effects on the MotionMote with the chinese PIRs and no users are having this issues, although the PIR and Moteino are in close proximity.
The new PANASONIC PIRs seem to be much better at this type of situation but I don't have empirical numbers to back up that claim.

[perky]

You could try putting a flat ferrite EMI suppressing core over the cable (I'd suggest trying either end, even both). My guess like Felix is the cable picks it up (conducted or radiated) and it gets rectified somehow to produce power supply noise at the PIR. If you have any ferrite toroid cores laying about try winding the cable through it a couple of times. You could also replace the wire antenna with a small 50R dummy load resistor to see whether it's radiated pickup, or move them far apart.

Mark.

[john4444]

Hi Ace,

I believe that your testing with the isolated supply indicates that the triggering is not caused by transmitted RF.
If noise on the supply is actually the situation then I would recommend isolating the supply to the PIR.
To isolate the supply to the PIR, add some resistance in series with the + supply.
I'd start with a 1K.
In addition, you will need 0.01, 0.1 and 10uF caps between + & gnd, close to the PIR.
The above will be a fairly simple and low cost test to see if "noise" on the supply is the issue.
(It is also possible that you may need to add resistance to the gnd connection.)
But, do that as a last resort. High ground resistance can cause other bizarre issues.)

Good Luck

[joelucid]

I had documented related issues in my magic carpet project: https://lowpowerlab.com/forum/projects/tino-magiccarpet-the-automatic-heated-carpet/

[captcha]

You could try putting a flat ferrite EMI suppressing core over the cable (I'd suggest trying either end, even both)

I use them on RG-58 coax for HF (<30MHz) and on CAT5/CAT6 Ethernet cables, but how effective would ferrite cores be at UHF?

[perky]

Choose the right ferrite material and pretty good, here are some flat cable cores from Laird that go up to 1GHz (suitable for 30MHz-1GHz):
http://www.lairdtech.com/products/28r1779-100

[captcha]

that go up to 1GHz

Niiice...   I always thought they were quite exotic when you go over 100MHz...  pricing isn't too bad..

Thanks for the link.