I have a 12x25 (300) matrix of IR sensors (to be used as proximity sensors). I need to be able to know exactly which sensor shows proximity and multiple sensors can be active at one time.
I have an Arduino Mega 2560 board with 54 I/O pins, which is obviously not enough.
Does anyone have any ideas about how to do this?
(I am relatively new to Arduino and "fancy" electronics)
Organize them as a matrix. You don't need them all at once, so 40 pins are enough to control the complete matrix. Although I don't understand how an IR sensor for itself can detect proximity.
Another way may be IO extenders, they exist in various versions using different CPU interfaces.
pylon:
Organize them as a matrix. You don't need them all at once, so 40 pins are enough to control the complete matrix. Although I don't understand how an IR sensor for itself can detect proximity.Another way may be IO extenders, they exist in various versions using different CPU interfaces.
If I use a matrix, then I could be pressing only 2 buttons, however, the Arduino would think there is a third being pressed because the rails of the matrix would intersect at another point.
Please post a link to the IR sensor, and describe how you intend to use one as a proximity sensor.
If an object is placed on the sensor, then the infrared light will bounce off and be detected by the IR receiver. The IR sensor then sends a HIGH signal.
Not a simple problem. The sensor presents either a HIGH or a LOW output signal, so a simple matrix cannot be used to combine several of them.
You can use diodes to isolate sensors sharing a single output connection, (called a wired OR connection) but you won't be able to tell the difference between one or more than one sensors active at the same time.
Here is an example of a wired OR connection for two outputs, A and B, that are active HIGH. Extend to as many outputs as you like.
The sensors will need to be multiplexed down to a smaller number of signal lines. 1-of-8 and 1-of-16 multiplexers or analog switches can be used.
The task sounds like it would be better done with CV.
If I use a matrix, then I could be pressing only 2 buttons, however, the Arduino would think there is a third being pressed because the rails of the matrix would intersect at another point.
No, because you don't check them at the same time. But are we talking about buttons now?
If an object is placed on the sensor, then the infrared light will bounce off and be detected by the IR receiver. The IR sensor then sends a HIGH signal.
No, not with that sensor. It needs some minimal distance to get a reflection. Keeping that distance is not easy, remember acrylic glas is not really transparent for IR light. Standard glas is a bit better but you'll get problem with reflections on the glas surface.
I agree with MarkT, computer vision is probably better fitted for the task, at least if my imagination of the setup is correct (the description we got yet isn't very detailed).
remember acrylic glas is not really transparent for IR light
Acrylic (PMMA) is completely transparent to near IR in my experience (certainly to IR capable cameras), I've even seen black acrylic that's fully transparent at IR, as the black dye was only blocking visible colours.
I suspect this fact is known and used by professional magicians.
My vote goes to shift registers - 300 inputs means you have to daisy chain 38 of them, but it's probably the easiest way of reading that many of those sensors.
Mind the power supply for your sensors: the schematic in that Amazon link suggests that each sensor uses some 40 mA (IR LED with 100Ω current limiting resistor plus a bit for the rest), that comes to 12A total at 5V!
MarkT:
Acrylic (PMMA) is completely transparent to near IR in my experience (certainly to IR capable cameras), I've even seen black acrylic that's fully transparent at IR, as the black dye was only blocking visible colours.
I suspect this fact is known and used by professional magicians.
The housing of IR photodiodes is black for the same reason.