Infrared Beam Break Project

Hi All,

I don't get much time for electronics but I really enjoy it when I do.

I just wanted to give an update of my latest project, it seems to be a common project on this forum and from the advice supplied I thought I would show you how far I have got.

Most beam break projects require the use of a "tube" to act as a collimator, I was able to find a sleeved cable grommet (Image1) which looks ideal.

Thing is I am not sure I need it as the IR Emitter I am using is the SFH4503 which according to the data sheet has a 8 degree emitting angle - please take a look at the datasheet and see what you think https://www.electro-tech-online.com/custompdfs/2008/10/84848.pdf

Anyway, take a look at the final project and let me know what you think, the infrared receiver is a Vishay TSOP34838 https://www.electro-tech-online.com/custompdfs/2008/10/46678.pdf (the resistor wheel allows me to control the current to the IR emitter)

The test environment is basically the back room of my house which is roughly 3 metres wide, from the initial test results I get the impression that the emitter I have can do a lot LOT better.

One query I do have though is that although the beam break circuit works fine I find that If I am within 12 inches of the emitter no beam break is detected. Having thought about this for a while I am guessing it is because the power of the beam is strong enough that at that distance it reflects off everyday clothing?

So I am going to try next to not only increase the distance but also reduce the 12 inch blind spot, one thing I may try is to reduce the duty cycle of the modulated pulse to see what happens.

Other ideas perhaps are to enclose the circuit in a dark box with perhaps a strip of infrared filter.

If anyone has any suggestions I would be very grateful.

All the best!

Mark

hi Mark,
I use the shorter version of the sleeved grommet to do exactly the same thing, there is one on the TX end as well as the RX.
Over a period of a few months the grommets tend to sag and partially block the beam, thats why I use the shorter ones.

The close 12" operation could be due to reflection from a surface behind the the detector, light does get thru the detector from behind, as its clear.

Also I use the detector diode with a 'dark' plastic body [daylight filter]

If you post your TX and RX circuits I may have a few ideas to increase the range, if thats of interest.

Hi Eric,

Thanks for your imput, the circuit itself isnt actually drawn out (but I could when I get home from work). The entire project is an 18F chip producing PWM to the attached circuit shown in the images.

basically comprising of:-
1. Detector - Vishay with the mandatory resistor and cap getting a 5 volt feed and producing the relevant output on one of the pins.
2. Emmitter - an OSRAM IR emitter enclosed in a grommet fed by the same 5 volt feed as the detector, the switching action is controlled by a transistor whose base is connected to a uC's PWM pin. The collector current to the emitter is in series with a variable resistor (a resistor wheel).

Thanks again.

Hi All,

As requested I have posted a schematic, not much to look at - its pretty much lifted from the reverend Goodwin's PIC tutorial site (minus a few smoothing capacitors).

Regards

Mark