I have a project in mind but I can't seem to be able to overcome a minor problem.
Following situation:
At work we are developing a credit card size box, containing a transponder, that a college, placed on the construction field will be able to carry on his person at all times. The idea behind this is, that you then will be able to put a receiver on the object you don't wanna come close to, an Excavator for example, and the "Box" will start giving of a warning sound if you get within a certain radius.
The setup at the moment is two Arduino nanos each running on a 9V Block Battery, the one attached to the transponder and the other to the receiver (normal stuff so far).
What we want to accomplish is limit the range of the radio waves to say 5m (safe distance to "dangerous" object) but the default signa strength is way too high . I thought about limiting the current to the transponder but, I quickly informed myself (online) about how inconsistent the signal strength would be.
I need a low power module that is in a car key for example that has a capped range, but I cant seem to find anything... that's why I'm asking here for help.
That is basically a very bad idea. You can't rely on any distance from a RF transmitter because there are lots of factors outside your control. Like what it is mounted on. So you would get a different range if you mounted it on a large metal object, and also if another metal object was close by.
Limiting the range of the transmitter, is not difficult, see my other post.
However your chances of getting a reliable proximetry alarm will be very slim in the circumstances mentioned.
Say you place the transmitter on the side of the 'Excavator' then for the alarm distance to be 5M when your on the opposite side of this very large metal object, the alarm might go off when your 25M (or further) away when your on the same side of the 'Excavator' as where the transmitter was placed.
This is the equivalent of attempting to use RSSI to reliably measure distance, which in the vast majority of circumstances is not practical.
Agreed there. Still i thought the way to reduce the signal strength would be to put an inductor on the antenna signal, but that box probably works just fine.
if the path to the danger is limited, what if you put also an extra beam of infrared light i mean if receiver gets rssi > certain level and receiver gets some of the IR pulses (althought) that is limited to how easy you can get pulses of IR light im not sure is feasible... well if you find a solution for this problem hehe ! everyone would be interested...