- Sat Jul 08, 2017 3:27 pm
#68090
To answer some questions...
The metal dish does cast a big rear sensor shadow as you'd expect, but I still wasn't able to creep up to it from behind - or any direction - without it noticing.
Obviously there is a trade-off between range and beam width.
If the sensors are at a slight angle to each other (Marty Feldman gaze) it provides a broader beam of reduced range, whereas max range is obtained when both sensors are square on to the target.
I expect max range and minimum beam width would be acheived by mounting the sensor(s) further out towards the effective focal point of the dish - but bear in mind that it's only a blanching dish, not a true parabola.
Besides, next I'm going to try using just a flat piece of metal as a reflector - which should give a wider sensor spread, reflecting everything forwards and diagonally outwards without being focused into a tight beam.
The physical range testing is a matter of connecting to the esp AP with a mobile phone, then diagonally zig-zagging away until the phone shows the sensor has lost signal, then zig-zagging sideways to discover the beam width. Sounds simple enough, but this dual sensor lash-up works so well that I found I was often moving out of esp wifi range (up to 50m) before moving out of sensor range.
So although I did try to see if earthing the electronics to the dish made any difference, I'm afraid there was no definitive results because the sensor range was already too good to be able to notice any improvement before losing esp wifi range.
That's good enough for me.
I only originally bought 5 of these sensors to evaluate, but I've already re-ordered a load more.
When the new lot arrive I plan to mount several to the same flat reflector - a couple close to the centre (as here) plus others at 3 o'clock and 9 o'clock facing diagonally out towards the side, and perhaps others to fill any perceived weak spots.
My thinking is that it may be possible to make something like a 'flower' sensor array capable of monitoring an area the size of a tennis court - if the range or sensitivity is too excessive in any particular direction then I can add metal screening if necessary... even if it makes it look a bit like a mailbox. A fun thing to try, anyway.
EDIT:
Incidentally, when time and weather permit, I'll try mounting a sensor inside an empty tin can to see if it's possible to make a very tight narrow 'spotlight' type beam specifically for aiming at a target of interest.
