Why do all PIR sensors come with a bunch of electronics attached to it

Thread Starter

zazas321

Joined Nov 29, 2015
715
Hey. I am looking for a more appropriate sensor for my application. I need to detect human hand inside a narrow area. I am currently using IR diffusion sensors panasonic cx-421 and they seem to work fine. However, they are quite expensive and have a very narrow beam.

I have been looking at PIR sensors for a while now, I have only tried this module so far:
1597812531630.png

and I can say that I do not really like the way it works. It holds the line LOW everytime its being triggered for 2.5seconds. In my application, the sensor needs to capture human hand very fast. A human putting hand inside a detecting area must trigger the sensor immediately and keep it triggered until the hand is removed. Once the hand is removed, the sensor must toggle off immidiately - no delay is accepted. I could not get this sensor to work fast enough.

Anyway, I could not really understand why these PIR sensors require so much additional hardware to function properly? I believe inside this module sits this sensor:
1597812698570.png

Looking at its datasheet, they suggest an application circuit;
1597812746838.png

Can I not wire this device directly to voltage supply and read its voltage directly from the output pin?
 

DickCappels

Joined Aug 21, 2008
6,640
Because an infrared pyroelectric sensor needs a lot of processing to detect the change of the charge on the sensor's surface. If you didn't have all that circuitry all you could get is a tiny (only a couple of tens of millivolts for a small device you) blip as infrared shined on it and when the light was removed. The circuitry amplifies the signal, detects the signal transition and pulls in the relay when the IR level changes. While you can still buy bare devices it is easier for many users to to buy a premade module than to build all that circuitry (that can be cheaply mass produced) and IR integrator.
 

ericgibbs

Joined Jan 29, 2010
11,073

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Thread Starter

zazas321

Joined Nov 29, 2015
715

Thanks for your suggestion. I have removed both of these resistors applied a blob of solder. Now I do not have a delay anymore which is cool.

However, there is another problem which Im trying to figure out now. Whenver I toggle the PIR sensor by moving my hand in front of it. It toggles the sensor output HIGH, however, after I have removed my hand away from the sensor, It still gives a few pulses for unknown reason.

Also, It does not hold the output low when I continously move the hand in front of the sensor. It just toggles the output fast which is not what I need.

I have tried placing the jumper switch in different position but did not seem to change anything?
 

ericgibbs

Joined Jan 29, 2010
11,073
hi,
As you may know the PIR module depends upon the movement of the radiating body, ie: the hand being detected due to 'shadowing' caused by the lens design.
Which in effect creates a low frequency signal which is then amplified.

You could overcome the rapid switching by driving a short delay retriggerable monostable.

E
 

PhilTilson

Joined Nov 29, 2009
86
Hey. I am looking for a more appropriate sensor for my application. I need to detect human hand inside a narrow area. ...
You don't give much information about the exact use you have in mind. If this is for some kind of safety device, why not use an interrupted beam approach, rather than a proximity sensor? Or, if the target area is reasonably enclosed, you could use reflected light from a hand. Both of these options would give you instant response and can be easily tailored to filter out 'flutter' etc.
 

djsfantasi

Joined Apr 11, 2010
6,944
You don't give much information about the exact use you have in mind. If this is for some kind of safety device, why not use an interrupted beam approach, rather than a proximity sensor? Or, if the target area is reasonably enclosed, you could use reflected light from a hand. Both of these options would give you instant response and can be easily tailored to filter out 'flutter' etc.
If I remember correctly from another thread, the TS wants to detect a hand entering a box of parts. He has a grid of boxes containing different parts and wants to track a person pulling different parts from different boxes.

He has been informed that his approach requires multiple picks for multiple parts. That is, if he needs two parts from two boxes, the person must pick them separately.

I think that the interrupted beam approach has been discussed in his other post. I don’t remember his reasoning for discarding that solution.

I think this is theThread
 

Thread Starter

zazas321

Joined Nov 29, 2015
715
Thanks for the answers all. I have not discarded the solution of using the interrupted beam sensor - in fact this is what I am using right now, but I believe there is a better way to do this.
1598242007993.png

What I use is something like that, The problem is that the box can be quite wide and most of these sensors have a very narrow detection beam. The solution would be to use multiple of those or use an area sensors that are sort of designing for this purpose. The only drawback of using these light array sensors is that they are often quite pricey ( 200-400$ per piece)
1598242096730.png
 

ericgibbs

Joined Jan 29, 2010
11,073
hi z321,
I know that you want to to detect a 'hand' inside a Lin Bin component box, could you say why this is required.?
They maybe an alternative solution.
E
 

Thread Starter

zazas321

Joined Nov 29, 2015
715
Yes. This system intends to help a warehouse operators pick&place required components to the boxes. I need to guide the operator from which box to pick an item (lighting an LED above the required item).

I need to be able to detect that an item has been picked from the box to initiate another box. I also need to keep track the number of items that I need to pick from that box and total number inside a box.

There are few options for me to detect that an item has been picked:

1. Weight sensor
2. PIR sensor
3. IR sensor

In my opinion, to make this system function properly, I need to be aware of 2 states:

1. User has put a hand in a bin
2. User has took a hand away from a bin.

If both of these states have been triggered , that means the item was taken from the box - I can proceed with an operation and toggle another box LED.

The program has a buzzer warming when a user tries to grab from a bin hes not supposed to. That is why its very important for me to keep the sensor latched when the user has put a hand inside a bin and keep it latched until he took a hand out of the box. I do not want the buzzer to activate while the person is still trying to grab an item from the bin.

I have no problems at all with the sensor that I am currently using which is Panasonic cx-421, however, this sensor only works properly for a small boxes since its beam is very small. If the big boxes are used for packing operation, I would need to put multiple of these sensors in a row ( basically making an array of sensors) to be able to certainly detect a hand. That solution is not an ideal since the price would be very high that is why I am looking for an alternative solution
 

ericgibbs

Joined Jan 29, 2010
11,073
In my opinion, to make this system function properly, I need to be aware of 2 states:
1. User has put a hand in a bin
2. User has took a hand away from a bin.
If both of these states have been triggered , that means the item was taken from the box - I can proceed with an operation and toggle another box LED.
hi z,
What if the picker fails to remove the component from the box.?
Hand in, then hand out.?
Perhaps a 3rd condition is required.
E
 

DickCappels

Joined Aug 21, 2008
6,640
Have you considered whether operation of the PIR sensor might be a problem, such as when the temperature of the machine/environment approaches that of the operator's skin?
 

Thread Starter

zazas321

Joined Nov 29, 2015
715
hi z,
What if the picker fails to remove the component from the box.?
Hand in, then hand out.?
Perhaps a 3rd condition is required.
E
That is true. The only way for me to make sure that user has taken an item from the box is to use weight sensor or have user confirm that he has taken the box by pressing a button
 

Thread Starter

zazas321

Joined Nov 29, 2015
715
Have you considered whether operation of the PIR sensor might be a problem, such as when the temperature of the machine/environment approaches that of the operator's skin?
I have considered that but havent put too much thought since I am not currently using PIR. I am using Panasonic cx-421 IR diffusion sensor.
 

ericgibbs

Joined Jan 29, 2010
11,073
That is true. The only way for me to make sure that user has taken an item from the box is to use weight sensor or have user confirm that he has taken the box by pressing a button
Hi,
You say there is a LED guide to the designated box.
If the picker has to press a button to extinguish the LED, after picking from the box, would that be good enough, assuming you have conscientious pickers.?
E
 

Thread Starter

zazas321

Joined Nov 29, 2015
715
Hi,
You say there is a LED guide to the designated box.
If the picker has to press a button to extinguish the LED, after picking from the box, would that be good enough, assuming you have conscientious pickers.?
E
The picker currently does not need to press any buttons. The LEDS work autonomously.

Once the operators starts picking operation, everything is controlled by raspbery PI server . Raspberry PI is sending a messages to remote ESP32 devices that are connected to individual bins. When raspberry PI activates a device , the green LED turns on and waits for the user to toggle the sensor. When the user toggles the sensor, the program understands that the item has been picked, turns off an LED an deactivates a device connected to that bin. Then raspberry PI sends a signal to a following device and activates another bin and that happens until the operation is completed. Once the operation is completed, everything loops back to the initial state and repeats
 

ericgibbs

Joined Jan 29, 2010
11,073
hi,
You did say:
That is true. The only way for me to make sure that user has taken an item from the box is to use weight sensor or have user confirm that he has taken the box by pressing a button
But
The picker currently does not need to press any buttons. The LEDS work autonomously
I am assuming a PI controlled LED on every box, cancelled by a picker push button on every box, after the box has been picked.

E
 

Thread Starter

zazas321

Joined Nov 29, 2015
715
I havent implemented neither the weight sensor or a push button yet. I was just saying that it would be the only way to confrim that the item has been taken.

At the moment, I just assume that everytime a sensors toggles ON and OFF, the item has been picked but as you mentioned this may not be a good idea.

So at the moment everything works automatically without any user input, the LEDS turn ON and OFF when a user toggles a sensor with a hand.
 

djsfantasi

Joined Apr 11, 2010
6,944
That is true. The only way for me to make sure that user has taken an item from the box is to use weight sensor or have user confirm that he has taken the box by pressing a button
This comment has been asked and answered, but I’m stubborn and obsessive. If the order requires three items, the picker must pick each item individually. Personally, I find this extremely inefficient.

Perhaps if a weight sensor is used in conjunction with the sensor, this problem could be mitigated.
 
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