IoT Visitor Counter
Two ultrasonic sensors in a doorway, an Arduino working out which way you walked, and a NodeMCU putting the room’s occupancy on the internet.
Built at Tinkerers’ Lab, IIT Bombay in 2019, to answer a question the lab kept asking out loud: is anyone in there?
Counting people is easy. Counting them directionally is the problem, and one sensor cannot do it — a single beam tells you something crossed, not which way it went. Two beams a short distance apart can, because the order in which they break is the direction of travel. The logic is entirely in that ordering, and the failure modes are all the human ones: two people abreast, someone loitering in the doorway, someone changing their mind halfway through.
The Arduino keeps the count and drives a 16×2 LCD. A NodeMCU does one job — push the number to Adafruit IO — which keeps the network code off the microcontroller doing the timing-sensitive work. The enclosure was 3D printed.
The same directional trick, two sensors and their ordering, is what the spin coater uses to know which way its motor is turning. I did not notice that at the time.
This one is archived — the feed it published to is long gone.
Gallery
0202
