SR-602 PIR sensor not working. Ideas ?

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  • Dannyx
    CertifiedAxhole
    • Aug 2016
    • 3912
    • Romania

    #1

    SR-602 PIR sensor not working. Ideas ?

    Good day folks. I'm trying to build a motion-activated light for my front door.....sounds simple enough. I had two SR602 PIRs on hand in my parts bin which I got for a similar project that never happened, so I thought these would be perfect to use here. They don't seem to work though. Either I'm doing something wrong or they're defective in some way...

    I power the sensor with a 12v wall-wart and use an SB8050 transistor and a 200ohm resistor between the collector and the "out" pin of the sensor to switch a 12v relay on and off....simple enough. It works, so there's nothing wrong with my circuit, but the problem is it keeps cycling on and off forever. What I did, according to the documentation, I changed the 0-ohm resistor to 56k to give me an on-time of around 11s. It's not perfect, but it's close enough - it's within a 2-5s error up or down, but that's acceptable. The problem is once the time elapses, the output pin stays low for about 2 seconds then comes back on by itself, again and again.....what gives ? I thought this may be like a "setup" time, but I left it alone for a good 5 minutes and it was still doing this.

    I tried the other sensor which I hadn't altered in any way and it's doing the same thing, except in smaller intervals, since it's still got that default 0ohm resistor for the on-time, so it comes on for 2 seconds, then off for 2 and so on...

    The strange part is that it only seems to do this when it's got the transistor's base connected to the output ! If I remove the resistor and let the output pin float, it works fine, as my multimeter shows !

    I tried adding some capacitors on both the output and the VIN pin, I even put a diode between the output pin and the transistor, but nothing helped ! It simply won't stay off for longer than 2s !

    Any suggestions, including some "better" small form-factor sensors ? Size is an important factor, since I could just run down to the local store and get one, but those are massive in size for my project !
    Wattevah...
  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 30917
    • Albion

    #2
    Re: SR-602 PIR sensor not working. Ideas ?

    test with a battery - incase it's caused by ripple.

    Comment

    • petehall347
      Badcaps Legend
      • Jan 2015
      • 4422
      • United Kingdom

      #3
      Re: SR-602 PIR sensor not working. Ideas ?

      have you put a flyback diode on the relay coil ?

      Comment

      • Dannyx
        CertifiedAxhole
        • Aug 2016
        • 3912
        • Romania

        #4
        Re: SR-602 PIR sensor not working. Ideas ?

        Originally posted by petehall347
        have you put a flyback diode on the relay coil ?
        Yes, it's the first thing I did

        Originally posted by stj
        test with a battery - incase it's caused by ripple.
        I shall, though I tested two different AC adapters....they could both be sh!t after all
        Wattevah...

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: SR-602 PIR sensor not working. Ideas ?

          .
          Last edited by budm; 12-18-2020, 03:17 PM.
          Never stop learning
          Basic LCD TV and Monitor troubleshooting guides.
          http://www.badcaps.net/forum/showthr...956#post305956

          Voltage Regulator (LDO) testing:
          http://www.badcaps.net/forum/showthr...999#post300999

          Inverter testing using old CFL:
          http://www.badcaps.net/forum/showthr...er+testing+cfl

          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
          http://s807.photobucket.com/user/budm/library/

          TV Factory reset codes listing:
          http://www.badcaps.net/forum/showthread.php?t=24809

          Comment

          • Dannyx
            CertifiedAxhole
            • Aug 2016
            • 3912
            • Romania

            #6
            Re: SR-602 PIR sensor not working. Ideas ?

            Originally posted by budm
            .
            I saw your original reply asked for the datasheet of the sensor. There doesn't appear to be one that's any different or containing more info than what I linked too in my starting post. All sources give the same info about choosing the value of the on-time resistor and some generic info but that's about it. For instance, one parameter which I couldn't find anywhere despite being important IMO is the maximum current the output pin can source ! It is unable to actuate a small 3v relay by itself, so I estimate it's less than 100mA.
            Wattevah...

            Comment

            • stj
              Great Sage 齊天大聖
              • Dec 2009
              • 30917
              • Albion

              #7
              Re: SR-602 PIR sensor not working. Ideas ?

              i notice the example schems for the part all show a 100uf smoothing cap

              Comment

              • petehall347
                Badcaps Legend
                • Jan 2015
                • 4422
                • United Kingdom

                #8
                Re: SR-602 PIR sensor not working. Ideas ?

                not that i think it will work but you could try a voltage divider on the relay driver transistor base .
                another thing to try is the light bulb circuit in the instructions .that at least rules out the relay circuit

                Comment

                • Dannyx
                  CertifiedAxhole
                  • Aug 2016
                  • 3912
                  • Romania

                  #9
                  Re: SR-602 PIR sensor not working. Ideas ?

                  Originally posted by petehall347
                  another thing to try is the light bulb circuit in the instructions .that at least rules out the relay circuit
                  It's virtually identical to what I have ATM, just with a relay instead of the lamp. True, the values are different...

                  Originally posted by stj
                  i notice the example schems for the part all show a 100uf smoothing cap
                  I tried adding one on both the VIN and the output, but didn't help. I THINK I saw a greater delay between cycles WITH the cap in place though, which makes sense since it takes longer to discharge into the base of the transistor...

                  Adding to the unpredictable and strange nature of the behaviour is that if I start the circuit with the base connected to the PIR, it cycles as described. If I remove the resistor to the base, it keeps cycling until I turn off the power and turn it back on again. It seems it doesn't like having something on its output pin, OR I'm drawing too much current with my 200ohm resistor, which I worked out to around 10mA for the S8050 tranny...
                  Wattevah...

                  Comment

                  • stj
                    Great Sage 齊天大聖
                    • Dec 2009
                    • 30917
                    • Albion

                    #10
                    Re: SR-602 PIR sensor not working. Ideas ?

                    unless it's buffered, i would keep it under 5ma - it's a low power device.
                    use a darlington transistor or a fet with it.

                    Comment

                    • Dannyx
                      CertifiedAxhole
                      • Aug 2016
                      • 3912
                      • Romania

                      #11
                      Re: SR-602 PIR sensor not working. Ideas ?

                      I think a 2n2222 has a higher gain, thus requiring less base current.
                      Wattevah...

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #12
                        Re: SR-602 PIR sensor not working. Ideas ?

                        So right now you have 4K7 resistor between the output pin and the Base of the relay driver transistor, correct?
                        If you hook up 4K7 resistor between output pin and ground, what Voltage do you see on the Output pin when it detects and not detects the object?
                        What is the resistance reading between Output pin and the + pin (measure when nothing is connected to the module)?
                        Last edited by budm; 12-19-2020, 03:10 PM.
                        Never stop learning
                        Basic LCD TV and Monitor troubleshooting guides.
                        http://www.badcaps.net/forum/showthr...956#post305956

                        Voltage Regulator (LDO) testing:
                        http://www.badcaps.net/forum/showthr...999#post300999

                        Inverter testing using old CFL:
                        http://www.badcaps.net/forum/showthr...er+testing+cfl

                        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                        http://s807.photobucket.com/user/budm/library/

                        TV Factory reset codes listing:
                        http://www.badcaps.net/forum/showthread.php?t=24809

                        Comment

                        • Dannyx
                          CertifiedAxhole
                          • Aug 2016
                          • 3912
                          • Romania

                          #13
                          Re: SR-602 PIR sensor not working. Ideas ?

                          Originally posted by budm
                          So right now you have 4K7 resistor between the output pin and the Base of the relay driver transistor, correct?
                          If you hook up 4K7 resistor between output pin and ground, what Voltage do you see on the Output pin when it detects and not detects the object?
                          What is the resistance reading between Output pin and the + pin (measure when nothing is connected to the module)?
                          No, I have a 200ohm resistor between the output pin and the base of the 8050....by my calculations (which could indeed be wrong), this was to give me around 10mA of base current.
                          Wattevah...

                          Comment

                          • budm
                            Badcaps Legend
                            • Feb 2010
                            • 40746
                            • USA

                            #14
                            Re: SR-602 PIR sensor not working. Ideas ?

                            If you perform the 4K7 (or 200 Ohms) connection between output pin and ground and check the Voltage at the output pin, that will tell you if it can drive the current you need or not.
                            Never stop learning
                            Basic LCD TV and Monitor troubleshooting guides.
                            http://www.badcaps.net/forum/showthr...956#post305956

                            Voltage Regulator (LDO) testing:
                            http://www.badcaps.net/forum/showthr...999#post300999

                            Inverter testing using old CFL:
                            http://www.badcaps.net/forum/showthr...er+testing+cfl

                            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                            http://s807.photobucket.com/user/budm/library/

                            TV Factory reset codes listing:
                            http://www.badcaps.net/forum/showthread.php?t=24809

                            Comment

                            • Dannyx
                              CertifiedAxhole
                              • Aug 2016
                              • 3912
                              • Romania

                              #15
                              Re: SR-602 PIR sensor not working. Ideas ?

                              WITH the transistor's base connected via 200ohm resistor, I measure 3.3v on the output pin, so it's not overloaded and dropping.
                              Wattevah...

                              Comment

                              • budm
                                Badcaps Legend
                                • Feb 2010
                                • 40746
                                • USA

                                #16
                                Re: SR-602 PIR sensor not working. Ideas ?

                                So yes, you are getting about 13mA Base drive.
                                Never stop learning
                                Basic LCD TV and Monitor troubleshooting guides.
                                http://www.badcaps.net/forum/showthr...956#post305956

                                Voltage Regulator (LDO) testing:
                                http://www.badcaps.net/forum/showthr...999#post300999

                                Inverter testing using old CFL:
                                http://www.badcaps.net/forum/showthr...er+testing+cfl

                                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                http://s807.photobucket.com/user/budm/library/

                                TV Factory reset codes listing:
                                http://www.badcaps.net/forum/showthread.php?t=24809

                                Comment

                                • Dannyx
                                  CertifiedAxhole
                                  • Aug 2016
                                  • 3912
                                  • Romania

                                  #17
                                  Re: SR-602 PIR sensor not working. Ideas ?

                                  I used worst possible Vbe loss of 1.2v from the datasheet, so in reality yes, it's probably closer to 13mA than 10mA, as the drop is less than 1.2v...
                                  Wattevah...

                                  Comment

                                  • Dannyx
                                    CertifiedAxhole
                                    • Aug 2016
                                    • 3912
                                    • Romania

                                    #18
                                    Re: SR-602 PIR sensor not working. Ideas ?

                                    Couple of other things I tried:

                                    -9v battery for power
                                    -FET instead of 8050
                                    -getting the relay off the breadboard in case the electromagnetic interference is affecting the PIR

                                    Neither worked: it still cycles....either these suck by construction, or I damaged them somehow....
                                    Last edited by Dannyx; 12-20-2020, 05:28 AM.
                                    Wattevah...

                                    Comment

                                    • Julian Tauscher
                                      New Member
                                      • Jun 2024
                                      • 1
                                      • Germany

                                      #19
                                      I had exact the same problem, running the SR602 with a CB3S Tuya Chip inside a "mini smart switch" from aliexpress. PIR was cycling on and off forever. OUT pin of the PIR was connected to TX1 (P11). So after changing it to P7 it worked normal. I have no clue what the problem was, checked for hours with impedances, capacities, oscilloscope and what not. Hope that might help anyone.

                                      What I checked:

                                      - Running just the PIR with battery and LED as Output: worked
                                      - Running with impedances and capacities within the CB3S mini smart switch: didnt work
                                      - Running with the CB3S but battery driven instead of AC power: didnt work
                                      - Running the PIR only with battery next to wifi device or AC wires: worked - no problems/interference here
                                      - changing input pin of the CB3S to P7: worked

                                      Comment

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