2 metre range sensor question

[kazimier]

hello

quick question - was wondering if anyone had much experience getting a good infra red signal working over a 2 metre range... need to build a circuit using ideally an infra-red emitter and receiver that can work across a 2 metre range and give an interrupt every time the beam is broken, i have done this kind of project before but never across such a long distance and am having problems getting a consistent result. I have played with the sonar sensors which work well across this range but annoyingly enough i need to retrofit this into a door frame which has a pair of  2 core cable running to either side, so need to use some kind of transmitter / receiver setup which only uses 2 wires for each one. any ideas?

thanks in advance

[Grumpy_Mike]

I would use a modulated IR beam and a reflector on the other side of the door. A TSOP4038 is the right sort of sensor for that.

[kazimier]

hey mike

thanks for your reply - sensor looks great but uses 3 pins.. it is really annoying trying to find a 2 pin solution to this problem - hence been looking at solutions like this: http://www.optekinc.com/datasheets/OPB100Z.pdf but the range is just not there / and not consistent..
will keep looking

[Grumpy_Mike]

One way of getting a two wire solution is to arrange things so that when the beam is broken a load is switched across the two wire power supply. Then at the other end you measure the voltage drop across a current measuring seriese resistor to detect a beam break.

[kazimier]

thanks again -
i actually managed to get the desired result by using a much more powerful IR led - seems to work - it is just real fidgety aligning the two over such a distance..