IR Proximity Detector

infrared proximity detector

Hi all.
I need help for a problem.
I have a little device that can turn on a LED when a person gets closer to it. The LED remains on for just 1 second.
I made reverse engineering and the schematic is in the attachment.
What I would need is that the LED could be on for all time the person is in front of the detector, not just for one second.
Is that possible? And if yes, how could I change the schematic?
Thank you all in advance.

ir proximity detector

7 transistors to detect a IR signal?....Just use one TSOP1738 and you'll get a low pulse continuously till it get the IR direct or by reflection. Good luck.

ir proximity sensor circuit

I suspect that this is a sensor for detecting body heat. The TSOP1738 is used for remote control operations, I believe. Since there is no concentrated IR source to detect, I wonder if the TSOP device would be useful.

These simple detectors are really just monitoring the entire heat distribution of the area they can see. They react to changing IR patterns.

The front end portion of the X10 motion detector is a similar circuit using a dual opamp. See the link below for the schematic.

https://www.edcheung.com/automa/ms14a.htm

The problem with the simple circuits is that after a short time, the hot body gets averaged into the background thermal profile. (If the circuit cannot track the background profile, then you get lots of false triggers due to temperature changes or sunlight heating up objects.)
Therefore, it is not easy to detect someone standing in front of the sensor for a very long time. Instead, you have to detect only the abrupt changes. When the body heat IR increases rapidly, you assume the person is present and turn on the LED. When the body heat IR decreases rapidly, you assume the person walked away and turn off the LED.

Since the X10 devices are inexpensive, I would suggest getting one of those to play with and modify. I would suggest that you will have to replace U1 with a micrcontroller that does the timings you want.

infrared proximity sensor circuit

Thank you both for your suggestions.
Banjo, you explanation is really interesting. Maybe the circuit I posted here is a pyroelectric one. I could realize that after a few search, and your post confirms that. It can't monitor the human presence, but only movements.
At this point let me explain better what I need. I would like to build a proximity sensor for a car alarm.
Do you think a IR proximity sensor like this one:
https://www.electronic-circuits-diagrams.com/alarmsimages/19.gif
could be good for my purpose?

ir proximity detector schematic

OK, The alarm link you provided is a reflective IR system since it has both a transmitter and a receiver. While this circuit could detect a person or really any reflective object for any length of time, is it really suited for a car alarm?

Think about all the possibilities:

1. Someone parks really close to your car, this will probably cause a false alarm.

2. Someone stands close to your car while talking on the phone for a long time, this will also cause a false alarm.

3. The crook could approach your car from any direction, yet reflective IR is very directional. How will you cover 360 degrees of area?

Typical car alarms use either a touch sensor or detect the interior lights coming on when a door is opened. This is a much more stable type of alarm. Below is a link for a sample device. There are many others.

**broken link removed**

If you are trying to protect a car in an enclosed area like a garage or carport, then consider a IR beam and reflector setup.

ir proximity sensor in presence of sunlight

Banjo, you're right.
I realized it's not a good idea to use that kind of circuit.
I will use something older but more stable.
Thank you for your help.

Can I use this car alarm circuit to measure distance? from 8cm to 40 cm is OK for me and 4cm presicion.

dumanmehmet said:

Can I use this car alarm circuit to measure distance? from 8cm to 40 cm is OK for me and 4cm presicion.

Click to expand...

May be a difficult task. Coz using IR, you can easily detect obstacles by reflecting IR or obstructing the path, but measuring distane is a bit tricky. You may sonsider Ulatrsonics for distance mesurements almost precisely.
Cheers

I have a project and I can only use IR LED. You are right ultrasonic sensor is the best but if it measures I have to make it. Do you know any circuit diagram that can measure distance? Regards.