Motion Sensor Device

"First I tested the device on the bench and it worked perfectly "

You mean that it was coming ON and OFF when there was a moving object in front of the sensor, on the test Bench?

If that is correct, then the sensor was working and should be OK. The problem might be from another place:

Too sensitive and some moving object in the area being covered, or some interference due to bad earthing in the building: If there are other devices (electronic) that are not properly filtered and/or earthed, they will pollute the mains wiring with spikes etc that can interfere with the sensor's circuitry (Cheap types Or too sensitive...).

Ex: Electronic ballast for fluorescent tubes (cheap quality from ...) not properly filtered or earthed...

You stated that the only pins that you left connected on the IC were V_CC and the output that drives the transistor.

Before you do anything else I suggest you go back and reconnect the ground pin of the IC. The position of the ground pin varies but it will either be the closest pin on the other side or the pin that is diametrically opposite the V_CC pin.

The IC will need power to operate and by not having the ground connected the whole IC will drift up to around V_CC which will more than likely why you are getting the 4 V that is causing the transistor to turn on and stay on.

Hi masu, yes I connected the ground pin but it does the same. When I disconnected the pins I did this one by one to see when the lights go off. The light turn off only when I disconnect the Vcc pin or the pin connected to the basis of the transistor. I understand, that I have to connect the ground of the IC otherwise the output will float.

The emitter of the transistor that drives the relay goes to ground

OK, then I gather we are working with a circuit that looks something like the one shown on the right.

If the transistor is working correctly you should see the following voltages when you have the indicated output from the IC

High Output from IC
TP1 – V_CC less 1.2 to 2.4 V depending on LED colour
TP2 – 0.1 to 0.2 V
TP3 – 0.7 to 0.9 V
TP4 – VCC less 0.7 to 1.0 V

Low Output from IC
TP1 – V_CC
TP2 – V_CC
TP3 – Less than 0.5 V
TP4 – Less than 0.5 V

If you are seeing these voltages then the transistor is working correctly.

Now getting back to the IC, if you are always seeing a voltage of around 4 V at the output pin regardless of whether it is detecting motion or not then it sounds very much like the IC is kaput, but to be certain we need to know more about it. I tried to find a data sheet for the part number you gave but nothing close came up. Are there any other numbers or symbols on the IC?

Would it be possible for you to post either a drawing or picture of the markings on the IC? If you could then I may have a better chance of finding the relevant data sheet.

Regards

Masu

Between TP1 and TP2 is the winding of the relay.

And yes there are always 4V at the output of the IC, that means the relay is always switched on.

The IC has 16 pins and under ICES49H is the number 9843K1485. No other symbols or markings.

The device was made in China for Radio Shack and CAT. No. 61-2606 is written on it. I,ll try to send you a picture.

Thank you for your help

Sorry for taking so long to reply, things have been a little hectic her, but I got the picture OK and it looks like it's a special batch of ICs that had custom part numbers put on it.

However, I did a search of passive IR drivers and the only 16 pin one I could find was an LSI Computer Systems Inc. LS6501P PIR Motion Detector. The link will take you to the data sheet for is so have a look as see if it seems to match your device.

On the other hand I have no idea where you would be able to get one of these so even if it is the right chip it may just be a further level of frustration.

Anyway, have a look and get back to us and I will have a think of what to do next.

Regards,

masu.

Hi masu, I'm sorry it is not the same but this LS6501P is a very interesting IC. If I could get one of tis I would like to make a pcb out of the schematic on the datasheet and use it instead of the bad one.

Thank you very much for your interest and the time you used to find this IC.

Best regards

Joachim

I have no idea how to get hold of them but they could come in very useful. The other option is to use a microcontroller. There are plenty of Microchip PIC microcontrollers that have inbuilt analogue to digital converters that could probably do everything you need. I'm using PIC16F90 microcontrollers to control all the lighting on a model of the Starship Enterprise that I'm building and because I purchased 20 of them I ended up paying about AU$3.⁵⁰ for them so they aren't very expensive . You will, however, need some way to program them and Microchip have starter kits called PICkit that have everything you need. I think the current one is the PICkit3 but they keep bringing out new ones all the time so it's worth having a look at their web site.

Getting back to the motion detector, I have always thought that a combined motion detector, smoke detector, Bluetooth interface, security camera, temperature & humidity sensor all built into a single unit that connects via a parallel serial bus would be very useful. By combining the functions at the detector stage you could combine the functions of security, fire detection and automation into one system rather than the usual three that duplicate and often triplicate the same thing. Being able to detect the presence of people in a room can save you a fortune in electricity by turning things off or down automatically when they are not needed.

Maybe one day when I'm totally bored out of my mind I might get of my proverbial backside and try to build one.

Take out the PIR sensor and see if the relay drops out with no sensor loaded. I had the exact same detector on my bench for a friend a few weeks ago and it turned out to be a noisy infrared sensor device. Replacements are available pretty inexpensively from China on auction sites.

Don