Alternative to Ultrasonic Array (LIDAR?)

[wfarid]

I'm currently using 5 Ultrasonic HC-SR04 sesnors in a row that spans 90 cm. They are mounted under a shelf, parallel to the floor. They are connected to an arduino uno & relay circuit that turns on a light when someone gets within range.

The main issue that I'm having with this setup is reliability. Sometimes the HC-SR04s will pick up the person and if they stand too still they will forget that the person is there. I have the polling quite frequently, but it seems to be more of hardware issue than software one. I've done a work around (setting up a 4 second timer), so that it's not rapidly switching on/off but even with the 4 second buffer sometimes the sensors won't detect objects.

I realized that the HC-SR04 don't like certain fabrics and get all sorts of crazy readings when they detect them. Which is unfortunate since this is supposed to detect people (who typically aren't roaming around naked).

PIR's would have the same problem of detecting someone standing still (since they only register changes).

What is the alternative to an ultrasonic rangefinder array?

I was looking at Pulselight's Lidarlite2 but it seems to have too narrow of a range (in terms of detection width, more like a small narrow beam).

Thanks for your thoughts!

 

[shrtrnd]

I don't know what-all they're using anymore, but the inexpensive security lights here (About $10 US),
people use to detect people in their driveway or on front porch, then activate a light, seem to work just fine.
I'd check into whatever they're using as a sensor. I assume it's infrared. In your application, the simplest thing
might be the best. Consider mounting a light beam with a mirror reflector at the other side of your detection zone.
Someone enters the zone, breaks the light beam, and activates a relay to turn on the light for as long as the
light beam is broken (with an appropriate delay-off). Stores here used them extensively in the old days to detect
a new customer arriving to trip a buzzer. You just want it to remain active until the person leaves the beam.
(You'd use a couple of mirrors if the detection zone covers a wide area.)
Somebody else here will probably offer you other ideas.
My opinion is that the simplest is often the best.

 

[wfarid]

I believe those lights that you are referring to use PIR, which I believe have an issue with lack of movement. If someone decides to stand still for 10 seconds, the PIR won't register them. Am I understanding the limitations of pir correctly here?

 

[shrtrnd]

No. You're stuck in high-tech logic.
What I'm talking about is a simple light source beam, that strikes a photocell detector target.
When the light beam is interrupted by the body of a person, the photocell trips a relay to activate an annunciator,
or in your case, a light for the person the photo-relay detects.
It's very low-tech, but not that long ago were used in most stores to let the owner know someone had entered his shop.
To cover a wide area, multiple mirrors could be positioned to direct the light source beam to the photo-detector.
Radio Shack used to sell the light-source and photo-detector as a pair for about $15 US. I've still got a couple
sets of them in my garage. They could be used as an alarm, or simple people-counter when the beam was broken.
I don't know if it would work for you, but it's cheap and simple.
When someone breaks the beam, for however long they're there, the photo-detector would activate a relay to turn the
light on for the person breaking the light-beam. You could use a delay-off of however many seconds once the person leaves
the area, and the light-beam striking the photo-detector again, would de-energize your light source for the person no
longer at the counter/table.