Human hand detection over short distance

Thread Starter

zazas321

Joined Nov 29, 2015
669
Hey. I am selecting a sensor to detect a human hand presence over short distance ( 1cm-30cm). A human will be placing a hand inside a box and ideally I will be reading sensor output in a digital form with my arduino and I will need to do something with that ( not important here).

At the moment, I am using Panasonic CX-421 Infrared sensor to detect human hand, however, this does not work very well because the IR beam is quite narrow and if person puts a hand in a box in a certain angle, the sensor wont even detect that. The solution would be to use 2 or more of those sensors in different positions to detect hand.

The problem with infrared sensors is that they detect any sort of obstacle and not specifically human hand. What I need is to detect human hand and nothing else - thermo sensor would be best but I could not find a right sensor that would just return me a signal based on if there is anything warm infront of sensor not.

So in short, I do not want my sensor to trigger if there is something in its path that is not a hand and in an accident scenario where the box collapses or something else happens where the box beforms and the distance between 1 side of the box and the other side gets closer, I do not want my sensor to toggle - that is why IR sensor is not an ideal for this solution

Would you be able to suggest anything else? Ideally up to 100$ for a sensor
 

jpanhalt

Joined Jan 18, 2008
10,221
That is a very difficult problem, if you really mean a "human" hand from a live person. How will IR or any similar method distinguish a human hand from some inanimate object or even a mouse?

Our hands are warm, have moisture, and emit vapors (smells). Some ideas:
1) Detect temperature change and profile. Our hands are close to or below 37°C. A dog's paw will likely be a little warmer, but a mouse will be about the same temperature.
2) Humidity will probably increase.
3) You might use sound reflections/resonances to estimate size.
4) There may be specific volatiles from humans not often seen with other animals (https://link.springer.com/content/pdf/10.1016/j.jasms.2009.01.012 ).
5) Movement per se will not distinguish animate from inanimate. Perhaps if the hand snapped its fingers, you could detect and analyze that sound or a particular gesture by image analysis.
6) A thermal camera and image analysis.

The latter three discriminators will likely require a budget way in excess of your budget. In brief, you need to define the question better.
 

Thread Starter

zazas321

Joined Nov 29, 2015
669
That is a very difficult problem, if you really mean a "human" hand from a live person. How will IR or any similar method distinguish a human hand from some inanimate object or even a mouse?

Our hands are warm, have moisture, and emit vapors (smells). Some ideas:
1) Detect temperature change and profile. Our hands are close to or below 37°C. A dog's paw will likely be a little warmer, but a mouse will be about the same temperature.
2) Humidity will probably increase.
3) You might use sound reflections/resonances to estimate size.
4) There may be specific volatiles from humans not often seen with other animals (https://link.springer.com/content/pdf/10.1016/j.jasms.2009.01.012 ).
5) Movement per se will not distinguish animate from inanimate. Perhaps if the hand snapped its fingers, you could detect and analyze that sound or a particular gesture by image analysis.
6) A thermal camera and image analysis.

The latter three discriminators will likely require a budget way in excess of your budget. In brief, you need to define the question better.
First thanks for the answer. I did not actually mean that I require to detect "only human hand" . What I actually meant instead, is that I need to detect a warm object.

For example, if a person puts a metal rod or something else inside the box, the sensor will not trigger.

What I have recently found are those PIR sensors (simmilar to Ericgibbs suggestion)
https://www.digikey.com/product-detail/en/panasonic-electric-works/EKMC4691111K/255-6297-ND/9356941

The one problem that I see with those, is that they have long sensing distance (2m-15m) and I only need to sense within 1 -30cm distance. If a sensing distance is much larger than 30cm , I might face some problems

Perhaps I will explain a little bit more about the project:
The system that I am building is something very simmilar to "pack to light". I will have multiple boxes in close proximity and I need to know in which box a human has put a hand. The problem with long sensing distance is that I might toggle the PIR sensor by moving a warm object "close" to the box and not actually putting a hand INSIDE the box.
 

Thread Starter

zazas321

Joined Nov 29, 2015
669
What also concerms me about those PIR sensors is that they only seem to work based on "heat source movement". What if the heat source is not moving for a brief second, would the sensor toggle OFF? If so, that is no good.
 

jpanhalt

Joined Jan 18, 2008
10,221
First thanks for the answer. I did not actually mean that I require to detect "only human hand" . What I actually meant instead, is that I need to detect a warm object.

For example, if a person puts a metal rod or something else inside the box, the sensor will not trigger.

What I have recently found are those PIR sensors (simmilar to Ericgibbs suggestion)
https://www.digikey.com/product-detail/en/panasonic-electric-works/EKMC4691111K/255-6297-ND/9356941

The one problem that I see with those, is that they have long sensing distance (2m-15m) and I only need to sense within 1 -30cm distance. If a sensing distance is much larger than 30cm , I might face some problems

Perhaps I will explain a little bit more about the project:
The system that I am building is something very simmilar to "pack to light". I will have multiple boxes in close proximity and I need to know in which box a human has put a hand. The problem with long sensing distance is that I might toggle the PIR sensor by moving a warm object "close" to the box and not actually putting a hand INSIDE the box.
Can't a metal rod be warm? What if it was sitting outside in sunlight?

If you want to detect warm objects, then use a temperature detector.

The MAX31856 is digital and has 0.008°C resolution. In an open room, it easily detects if I stand near it or if the fan is on in an adjacent room that has an outside window..

https://datasheets.maximintegrated.com/en/ds/MAX31856.pdf
 

Thread Starter

zazas321

Joined Nov 29, 2015
669
Can't a metal rod be warm? What if it was sitting outside in sunlight?

If you want to detect warm objects, then use a temperature detector.

The MAX31856 is digital and has 0.008°C resolution. In an open room, it easily detects if I stand near it or if the fan is on in an adjacent room that has an outside window..

https://datasheets.maximintegrated.com/en/ds/MAX31856.pdf
It can be, but most likely, in my scenario, the objects that will be put other than a hand will not be warm. I am mostly concerned with the fact that if the box deforms (sides get closer to each other) , I do not want the sensor to toggle which is where PIR would work I guess. The only problem with PIR is movement. If persons puts a hand inside a box and holds it still, the PIR might turn OFF which would cause error because the hand is still in there
 

Thread Starter

zazas321

Joined Nov 29, 2015
669
I read the datasheet that Eric posted and you can adjust turn on time from 5-300 seconds.
That would not work for this project because I do not know when will be the next time when the person will put a hand inside a box ( might be after a couple of seconds or minutes)
 

Thread Starter

zazas321

Joined Nov 29, 2015
669
the box is about 30x20x20
The item specification suggest the sensing range is 3m-5m, so im not sure how would it work in my scenario. I do not want to detect if a hand is near the box - only when its inside. Perhaps covering a side that is facing out the box would prevent this from happening.
 

ericgibbs

Joined Jan 29, 2010
10,767
hi
Is it an array of boxes and could there be more than one person accessing a different box at the same time.?
E
What is in the box.?
 

Thread Starter

zazas321

Joined Nov 29, 2015
669
hi
Is it an array of boxes and could there be more than one person accessing a different box at the same time.?
E
What is in the box.?
Yes there will be an array of boxes. Lets say like 3 rows 5 boxes per row. So 15 boxes in total. Only one person will be accessing boxes at a time.

Inside a boxes there will be various items from various types of electronic components to plastic parts , tools and etc
 

ericgibbs

Joined Jan 29, 2010
10,767

Thread Starter

zazas321

Joined Nov 29, 2015
669
I have but the problem with IR is that they activate when they sense any object in front. In the unlikely event of box falling/deforming or any other problem with the box , I would ideally not activate the sensor.
 

Thread Starter

zazas321

Joined Nov 29, 2015
669
Also, since the box opening for putting a hand inside the box is quite big, the problem with IR or laser sensor is that they might not pick up a hand if you put it in a certain angle or certain side of the box
 

Thread Starter

zazas321

Joined Nov 29, 2015
669
So the final system will look somehow like this:
1594902155735.png

For testing, as I mentioned , I am using panasonic cx-421 sensor which is diffuse reflective sensor that is shooting an IR beam which reflects from a closest surface and returns to the sensor.

NOTE THAT THE BOXES THAT I AM USING NOW ARE SMALLER THAN THE ACTUAL FINAL DESIGN BOXES
If I put my hand straight in front of the sensor , the sensor will activate (Orange light)

1594902095334.jpeg

If a hand is slightly below the IR sensor, it wont toggle:
1594902156437.jpeg

Same happens when person puts his hand above the sensor - it wont toggle.
As I mentioned before, this could be fixed by adding a 2nd IR sensor above or below to sense the hand from 2 angles. That is not a bad solution but not ideal for me as IR detects any obstacle and I want to detect a human hand. If lets say there is like a piece of wire or any component sticking out too high from the box or too close to the IR sensor, Ideally, I do not want that to toggle the IR sensor and that is why I am looking for some other solutions if possible.
 

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