In my project, i am about to impose speed limits on vehicles…!! keeping a transmitter in the road side (in the zone) and a receiver inside the vehicles, a data should be transferred from transmitter to the receiver which will impose the corresponding speed limit…
If the zone is like a school zone or a hospital zone, an RF transmitter can be kept at the center which may transmit the data centrifugally. But if it is a long straight road, say 1 to 2 km in which i should impose speed limit, an RF transmitter cannot be used… because, if there is another road, parallel to it (in which, the speed limit is not necessary), the RF data transmitted will affect the vehicles in both the road(since RF dont hav directionality), which is not a necessary one… here, IR can be used…, on the entering side of the road., IR transmitter can be kept which will impose speed limits and in the end of the road, another IR transmitter can be kept which can RESET it and make the vehicle free… But, if IR is used, if a vehicle overtakes another vehicle in that place where v had kept the IR transmitter, then the data cant reach the overtaking vehicle as it wont be in direct contact with the vehicle…
So, like these., there r many advantages and disadvantages in all the communications or protocols… i want to make a comparison on all these and want to choose the effective way… so, whatever u think as the adv or disadv, pls say to me, it will help me… it may be in cost, properties, license issues, security problems, etc… in IR or RF or protocols like ZigBee or WiFi, etc…
n1ist:
What about using GPS to determine where the vehicle is, and use a lookup table to get the speed limit for that section of road?
/mike
I thought of the same… but., can we manage all the vehicles at the same time??? means, all the vehicle should send their positions (calculated by the Gps) to a common place which then should send signals to control the speed of the vehicle…!! so the data base should be maintained in a particular area and to that area, each and every vehicles should send their Gps info each and every second, which may be difficult…
Or else, one more possibility we have…, we should store the data base in the vehicle once and if necessary, the newly added or removed or such modifications should be Updated to the vehicle through some communication again… then, what u say will be a very effective one…
Thank you very much for ur suggestion and waiting for further suggestions…
n1ist:
What about using GPS to determine where the vehicle is, and use a lookup table to get the speed limit for that section of road?
/mike
Or else, one more possibility we have.., we should store the data base in the vehicle once and if necessary, the newly added or removed or such modifications should be Updated to the vehicle through some communication again.. then, what u say will be a very effective one...
Thank you very much for ur suggestion and waiting for further suggestions…
The above would be the way to do it with a GPS based system. My guess is that’s the best way. A different take on your original idea is to have “gates” at the start and end of each speed zone. The “gate” is actually a low power RF transmitter. Any vehicle coming within some short distance (? perhaps 50 feet ?) would be guaranteed to receive the transmitted RF signal. This signal might be the speed limit or it might be a gate ID number, which the car would then use to lookup the appropriate speed limit. At the end of a speed zone another RF transmitter would inform the car that it had passed that “gate”. So long as the roads are separated by more than the RF range, you will avoid the problem in the OP (where you transmitted data centrally). The concern then is keeping all the speed limit data up to date, should/when a speed limit changes. And of course keeping the system working when someone decides to disable their RF receiver or a “gate’s” transmitter.
Lastly a car carries around with itself, it’s own source of power. Multiple “gates” will each require a source of power.
BTW : RF does have “directionality”. You’d most likely want to use some type of directional antenna (space permitting) to send more RF towards cars on the road than towards other directions.
Ya, i agree with u… What you say is right, instead of keeping IR transmitter, if v keep a low power RF transmitter, it will work as how u said… But, if in that part, if we use RF transmitter, we should get licence to use that particular frequency… We cant use the frequencies like 88-108 Mhz which we already use for FM here in India… so, we should go for some other frequency, get licence for it and should use it( i am saying this in case of real time situations., but for demo purpose we can use whatever frequency we wish for)… Wont it be difficult…? Or, wont there be any security problems like some other people can use that frequency to impose speed limit in unwanted areas and cause some crimes…??
I just wanted to clearify all these doubts before i fix upon any techniques… So, pls help as far as u can… I will be thankful for it…
Of all the discussions above, pls Say me which one will be the best…, either GPS method or RF method or any other different methods… Pls say me reasons for whatever u say…!! however simple or complex the reasons may be, it will be very helpful for me…
I did a similar project using a GPS module and an ATmega328. The microcontroller contained hardcoded speed zones defined as polygons, so the solution knew whether the speed limit was being exceeded or not. With this approach no communication with any other device was necessary (other than the GPS satellites, that is).
