Infrared - 2 Transmitters and 1 Receiver

[UTMonkey]

Hi All,

This no doubt is definitely beyond me (at the moment) but I wanted to get some input.

Can a single infrared receiver determine simultaneous signals from 2 infrared sources?

Requirement
I want to design a circuit which not only detects a break in an infrared beam but also is able to determine the direction of the object breaking the beam.

Hence the need for 2 transmitters (left + right) so:

Left Broken + Right Unbroken = potential motion L to R set L2R latch
Left Broken + Right Broken + (L2R set?) = Definite L to R, do something, clear L2R
Left Unbroken + Right Broken = potential motion R to L set R2L latch
Left Broken + Right Broken + (R2L set?) = Definite R to L, do something, clear R2L

Left Unbroken + Right Unbroken = All bets are off, clear all latches.

What do you think?

 

[blueroomelectronics]

Well with two sensors it's called a quadrature encoder.

 

[Nigel Goodwin]

Do it the other way, have two receivers and a single transmitter - or syncronise the two transmitters to send at different times, and send a digital ID each.

 

[UTMonkey]

No doubt you will have guessed how little I know about signals et al. But what would happen if both of the transmitters were placed on the same circuit in very close proximity (1cm) and contributed to an aspect of the final signal.

See attachment

 

[JTECH]

Rather use 2 beams, i.e. 2 transmitters and 2 receivers. At the receiver outputs, do the logics for the sequence of events. eg. L to R = up-counting and R to L = down-counting etc.

 

[UTMonkey]

Thanks JTECH, but what would stop the signal from one TX going into the other RX?

 

[3v0]

The problem is that you can do this several ways.

When using multiple TX RX pairs activate one TX at a time. Ignore any RX not paired with the active TX. When done fast enough the resulting information is the same as if all the pairs were active. (up to a point/speed)

You could use a single TX and 2 or more RX. That would allow you to sense direction by the order in which the RX units went silent.

A uC would make life easier.

 

[UTMonkey]

I think a Microcontroller is a definite solution.

Are you saying that the uC would would flash the TX and then check the RX virtually simultaneously(?), then if no RX signal you could assume the beam is broken?

 

[JTECH]

Thanks JTECH, but what would stop the signal from one TX going into the other RX?

Focusing directional beams and using short lengths of tubing at the receiving IR Diodes might help. Also keep beams apart (perhaps 300 mm?).

 

[UTMonkey]

300mm is a bit wide, It might be able to register me (yes I ate all the pies) but not someone like posh spice.

 

[JTECH]

True, one just have to experiment to find a reliable distance apart. 300mm was only a suggestion as an example. I am sure some of the other guys will have better and alternative solutions.

 

[3v0]

I think a Microcontroller is a definite solution.

Are you saying that the uC would would flash the TX and then check the RX virtually simultaneously(?), then if no RX signal you could assume the beam is broken?

You can setup the uC to generate the right freq via the counter/timer/PWM hardware. Once started the hardware will produce the signal without processor intervention. This makes it possible to generate the signal and detect it with the same uC. You start the signal, check to see if it shows up on the RX, then stop the signal.

 

[UTMonkey]

That sounds pretty cool, I have'nt even started looking into uC's yet but this response sounds like I had better get on with it.

Regards

Mark