Hello all. An interesting "problem" came up and I thought it would be interesting to explore.
What I am looking for is a unit/circuit that will transmit a signal (at least 200m and not line of sight). Also a receiver that detects the signal and will sound an alarm.
In effect I am looking to make some sort of proximity sensor.
Any ideas?
Can we get some 'refinement' on what it is you wish to do - a) detect motion or something within 200 meters, or b) send that kind of info (alarm activation) over a 200 meter path?
There are possible (as well as impossible) solutions to both, and it would help to refine the requirement a little bit more.
Jim
No problem, we would like to find a cost effective solution to a safety concern for Rally racing. We want to have a beacon transmit a signal if the car is stopped on the stage, crashed or some other danger. The occupants can turn the beacon on, and this will send out the signal. The next car on the stage (typically 1 to 2min behind) will get an audible and or visual alert that they are coming up to a possible blocked road. At the speed we race at, 100m is the borderline for distance to react to something around the bend or over the next crest.
There are a few systems on the market that do this, but they are all either VERY expensive and or have issues with reliability/poor support from the manufacture.
Think of it as a panic button that any receiver in the area would receive.
Okay, understand, kinda like Sentinel Safety device, less like IriTrack device ... descriptions for others can be found here:
Dakar Tech; Iritrack, GPS, Sentinel, Emergency Beacon... - ADVrider
You have an interesting project/goal in mind.
In the USA one might recommend using MURS (2 Watt power level at five frequencies near 152 MHz) frequencies or FRS (.5 Watt power level, but restrictions on how the radios are built, like requiring a built-in antenna, but this is not such a big handicap to overcome) or CB (5 Watt AM at 27 MHz, but, too much interference with sun spot cycle on the upswing).
There are also bands like 900 MHz available if Spread Spectrum (1 to 2 Watts power) techniques are used. And even 2.4 GHz, but line of sight starts to become an issue on 2.4 G partly because of frequency (absorption in vegetation, etc)
Seems like something could be worked up, especially today with chips that do a good job of signal strength measurement (if your system uses signal strength to roughly 'compute' a distance for protection distance) or maybe 'beacon' your GPS coordinates and drivers coming up would receive this and then their unit would calculate how close your were. This last approach would require a GPS receiver, but, could be engineered to give repeatable, and predictable results.
Jim
Thanks for the reply.
I think that the system would be used as an addition to the safety procedures already in place. The what ifs are endless. False positive is the worst thing that can happen. If the alarm goes off without there actually being a car in distress. the crew begins to doubt the unit and then its a total waist of everyone's time and money.
This project is beyond my technical ability (to do it properly). If someone is looking for a "project" I can provide a test group and potential market that is for certain. If the price per unit could be kept under control, and reliability proven. It would be a very valuable item. In my area alone we would be looking at 30+ cars. Plus if its adopted as a required piece of safety gear our race series has over 100 active cars.
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