Multisensor PIR based on IKEA Molgan

[tomkxy]

@TimO said:

@tomkxy Nice write up! Do you have an idea on the accuracy of the humidity sensor within the case?

I just put it up in my one of my rooms. It works at least at a distance of about 4m. I will try to do some measure at what distance it is working. I'll post the results.

[tomkxy]

@TimO said:

@tomkxy Nice write up! Do you have an idea on the accuracy of the humidity sensor within the case?

Sorry, just saw that you asked about the humidity sensor. No, I have no idea yet. Need to make some comparison measures.

[korttoma]

@tomkxy did you really need the voltage divider? I think the sensebender does a decent job of measuring battery percentage by default.

[dynamite]

@korttoma As far as I can see the sensebender is fed by the 3 volt of the PIR. So you can not use this as a reference for voltage measurement.

[dynamite]

@TimO @tomkxy I have the Dallas sensor within the case. The reading follows the same line as other temp sensors within the same room. No big delay or something. The only downside is that the PIR is mounted on the roof, so temp is always a bit higher.

[tomkxy]

I just realized that I see a lot of false triggers. Anybody else having that experience? Any idea how sensitivity of the PIR can be reduced?

[dynamite]

@tomkxy You can change the sensitivity of the PIR. You have to change the value or R15. See here for a datasheet of the BISS001
But I do not know whether you should increase or decrease it...?
If you did not modify your PIR then the PIR will stay high for 30 SEC. What is the period between the false triggers?
Could it have to do with powering your sensebender from the powersource within the PIR and not directly from the battery?

[tomkxy]

@dynamite I see no clear pattern for the false triggers. Most of the time it is after about 7 minutes. But not strictly. Sometimes more than a half hour.. Well if I would power the sense bender directly from the battery I either would have to use a regulator or remove one of the batteries. Would the PIR still work reliable with about 2.4V? Would it make sense to try a capacitor between the 3V where I power the sense bender from to ground?

[dynamite]

@tomkxy The range of PIR is 3-5V so most probably 2.4 V will give some trouble.

[Yveaux]

@tomkxy you can just use 3 batteries to power the pir and only 2 to power the atmega and radio. Just c
Use the same ground on them, and tap the arduino power after the second battery.
I have some pirs running this way and they work just fine!

[dynamite]

@Yveaux @tomkxy You were one step ahead of me, I was just thinking of that solution. At the moment I am also preparing version 2 of the MOLGAN PIR based on Arduino pro Mini I will check on the false positives as well. But I will feed both the PIR and pro Mini directly from the three batteries.

[tomkxy]

@Yveaux @dynamite Thanks for your suggestion. I followed @Yveaux suggestion and tapped the power for the sensebender after the second battery. It is now working for 2 hours without any false triggers. I will continue the test (for test purposes the sensor is sitting in a room with usually has no movement).

[Yveaux]

@tomkxy :+1:
The same setup is working fine for me for quite a long time now!

[tomkxy]

@Yveaux Unfortunately, I still get false triggers. Do you also use a sensebender? Any ideas, what I can try. I tapped into as you suggested to the second battery.

[Yveaux]

@tomkxy I have some ProMini's (8Mhz) with regulator bypassed which are 2xAA fed in this way.
The PIRs are HC-SR501's, also with the regulator removed and 3xAA fed.
I haven't tested this setup on the Molgan's yet, but assuming the IC's are both BISS0001 I expect results to be identical.

Here's a picture of my setup:

(Btw. components on the HC-SR501 have been moved to the side to decrease the unit's depth)

[Yveaux]

FYI, I measured power comsumption on the Mogan when sleeping with and without regulator.
The power consumption was significantly less with the voltage regulator, then when directly powered from 3xAAA (regulator removed).
Therefore, my Molgan hack board design targets to use the PIR with regulator (3xAAA input) and the ATmega+nRF powered directly from 2xAAA.

[dynamite]

@tomkxy I Will put mine for a test run online tonight in the closet. If no trigger than it should be ok.
Edit: did something wrong when removing led from pro mini so some debugging is required.... No testing tonight :cry:

[tomkxy]

I googled a bit regarding PIR false alarms and found a couple of links. Apart from small bugs - which I have not in the room - air vents could trigger false alarms. Thus, I put back the plastic dome and now have sind 4 hours no false alarms. I am now convinced that my false alarms a most probably triggered by placement and may be air vents.

http://de.actmeters.com/advice/five-causes-of-pir-false-alarms/
https://www.youtube.com/watch?v=h0bp91xy5vY
http://www.hkvstar.com/technology-news/how-to-install-pir-sensor-minimize-the-false-alarm.html

[Yveaux]

@tomkxy of course you should always mount the fresnel cover. It focuses the incoming IR on the sensor and forms a barrier. Without the cover the sensor will always be more sensitive and have a much smaller field of view, increasing sensitivity even more.
If an unmodified Molgan doesn't suffer from false triggers, a modified one also shouldn't.

This is one more confirmation of the importance of describing your setup accurately :smirk:

[tomkxy]

I made a couple of additional modifications based on posts here and google results:

• put a short wait before the node goes to sleep -> based on reports from that forum
• read the motion pin twice with a small wait in between
• put a small alu foil between the radio and the PCB -> there are some reports in the internet that RF interference could cause false triggers

I had a close look at the sensor today and everything looked okay so far. However, I was moving into the room in and out. Let's see what the result tomorrow will be.