PIR sensor with nRF24L01+ transmitter gives false alarms if supply voltage over 2,98 volts

  • Hi everyone!

    I am building a sensor network system based on nRF24L01+ transmitters and I have a problem with my PIR movement detection sensor. The sensor consists of,

    • Arduino Mini Pro 3.3V with voltage regulator and LED removed
    • Seeedstudio SEN-116A2B PIR sensor with voltage regulator removed
    • Dallas DS18B20 temperature sensor

    The sensor is transmitting temperature, PIR movement status and battery voltage every 15 minutes, in between that the Mini Pro is sleeping only detecting PIR movement that is wired from the PIR out to pin 3 of Mini Pro and handled as an interrupt in the code.

    The whole setup worked for perfectly for days on 2 used AA batteries with a voltage between 2,97...2,94 volts. Then I at some point put in fresh batteries with a voltage around 3,1 volts.

    With the fresh battery voltage the PIR started to trigger by itself in about 4...5 second cycles!?!? What could the reason for this be? Any correction suggestions?

    So far I have found out the following,

    • if I disconnect power from the nRF24L01+ transmitter the PIR stops self triggering
    • a smoothing capacitor on the nRF24L01+ power pins is of no help
    • if I supply separate 3,1V battery power to the nRF24L01+ from a second battery set everything works OK
    • the problem starts randomly to occur if I supply power at a voltage over 2,98 volts and at about 3,05 volts it is continuous

    I have now spent two days trying to solve this problem with different capacitor additions in the power supply line but nothing I have tried has helped. Anyone had a similar problem and solved it?

    Any help greatly appreciated!

  • Just thinking out loud...did you remove the diode from the PIR? I removed both the PIR regulator and diode and run it off a boosted 2AA (3.3V) circuit and it works fine, so far....It seems the radio, when it powers up, causes some kind of voltage irregularity. Maybe a bigger low ESR cap? I found that adding caps between the VCC and GND pins of the radio reduced the magnitude of the voltage oscillation from a booster, but adding the 220 Β΅F low ESR cap reduced the magnitude and frequency, and improved the radio communication greatly. I know that is not your problem, but it seems that it could all be related.

  • Did you power the nRF24 direct from the 2AA batteries?

  • I have povered the circuit both from batteries, a step up converter and from an external power supply. In all cases the PIR self trigger problem starts when the voltage is higher than about 2,98 volts...

  • Contest Winner


    how do you have it wired?

    what is connected to each pin?

  • Hero Member

    Looking at http://www.instructables.com/id/PIR-Motion-Sensor-Tutorial/ I see the PIR has a BIS0001 IC on it and according to it's datasheet it has a supply voltage of 3 ~ 5 Volt.

    You write you have the voltage regulator of the PIR removed, then it is luck it is working when powering it below 3 Volt πŸ˜‰

    One other thing I see in the datasheet is:

    Description    |          Range     | Unit
    Input voltage  |  Vss-0.3~ Vdd+0.3  |  V

    Could it be that if you supply power at a voltage over 2,98 volts you come outside this range?

  • I have the same problem as long as the voltage is above 3v the sensors work right. The moment the voltage get to 2.98v I get false triggers. I run my sensor of 2 aa battery's and my sensor is setup as per this forum link http://forum.mysensors.org/topic/225/hc-sr501-motion-sensor/13. I order a step up voltage supply to see if it this will solve the problem once the battery goes below 3v.

  • I'vr git exactly the same probleme and I dolce it withe a step up 3,3v just for the PiR. I think the chip if the PIR really need 3v IR higher and below 3v it give false alert. You get exactly the same error by giving 3,3v to a 5v PiR with rΓ©gulator.

  • At first I didn't understand why this was happening I was thinking it could be voltage but was not sure till I see this discussion now I know if the voltage get to 3v its time to replace the battery's.

  • Hero Member

    Weird. I have a motion sensor node (regular Ebay PIR model) that I run off of 2xAA batteries. It has been running since early October at least, outdoor in all sorts of weather including sub-zero temperatures which could impair the batteries and that node is still alive and well.

    Unfortunately the voltage measurement (voltage divider circuit) must have failed somehow since it stopped reporting after the first week or so, but surely the voltage must have dropped well below 3V by now. Alkaline batteries have an alarming initial drop of voltage if I've understood things correctly. Also, I bought some supposedly very good batteries (top tested, from Clas Ohlson here in Sweden) and the initial voltage was in fact well above 1.6V a piece (not that it is much to brag about since the voltage drop will just set in anyway). Even a total of 3.2V did not seem to matter for the sensor.

    Just waiting for the voltage to drop low enough to trigger false alarms though. It really is inevitable and a good example of why we need a good boost/step-up circuit.

    I have my power connected to the "H-pin" btw still and have not dabbled with removing any regulator or diode.

  • @bjornhallberg can you measure the voltage on your batteries it will be great to know what you're voltage are.

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