Synchronization among receivers and tranmitters
hi
At the receiver side we have receiver and 50 meter away from the receiver site there is a magnetic filed line embedded into the road, So when a car crosses the magnetic line it will detect the field and on-board controller (in the car) will get interrupt and will ask the transmitter to transmit the ID.
Now there are 2 situations
1) At a single time 2 or 3 or 4 cars can cross simultaneously.
2) One car will cross the magnetic lane at one time, the second car is at 200 meter away from the frist one. so the third car is 200 m away from the second car.
What is the best way for implementation of this system?
can i use different transmitter with one broadband receiver?
The obvious way is to use one receiver per transmitter. The receivers must be narrow band so they only respond to their own transmitter. Their linearity must be good enough so they are not overloaded by having , say 10 transmitters being received at once. Because all the transmitters must operate on about the same frequency, you have the choice of going for a precise carrier frequency, being matched by a precise receiver frequency or precise modulation frequencies. A digital system could be implemented using different clock frequencies, but it would be difficult to implement.
Frank
Airports have a similar problem. The air traffic controller cannot hear two pilots simultaneously on the same frequency, because their broadcasts jam one another.
It is ideal to have 50 receivers and 50 broadcast frequencies. However you probably prefer a single frequency and single receiver.
Suppose you broadcast on only one carrier. Data is encoded on 50 different frequencies which modulate the carrier. The receiver needs 50 bandpass filters.
Each car must only transmit for a brief moment. Even then it is possible for two cars to jam each other. You might get success by making a car broadcast repeatedly all the time it is over the line. It waits for a random idle period in between.
One way to do this is to have one master transmitter that transmits a signal to all cars on the one frequency, each car having a receiver tuned to that frequency.
The master transmitter then asks each car in turn if it has any data to transmit.
Each car recognises its own particular code, and replies with any data when called.
The master transmitter calls up each car, then listens for a reply.
That way only one car can talk at any one time.
Thanks for reply.
May i use nRF24L01 module. It has a mode in which it can establish pipeline with 6 similar nRF24L01 modules.
i need more explanation for
"A digital system could be implemented using different clock frequencies, but it would be difficult to implement.'
if you receive two digital streams with slightly different bit rates, you end up with a pulse stream which has variable mark space ratios and amplitudes. For example suppose one channel has a steady 1:1 square wave at a bit rate of 1mS, the other channel has the same but the bit rate is .9 mS. The output of the receiver could be 1V for .1 mS, then it rises to 2 V for .9mS, then it falls to zero for .9 mS, then rises to 1V for .1 mS, then 2V for .8 mS. So you will have most of the transitions (except where they coincide) and you will have the changes in amplitude as pulses overlap (or not). So the microprocessor could look up the transitions times in a table. In the above example they would be N X .1mS. The trouble is the table would be huge for 50 cars.
I think I would go with precise audio tones and use analogue filters in the receiver.
Frank
@chuckey
Can you help me?
May i use multiple NRF nRF24L01 transceiver module , instead of implementing precise audio tones and use analogue filters in the receiver.
And how "precise audio tones and use analogue filters in the receiver"can be implemented? Ithink there is lm567 tone detector ic. but in this case we need 40 tone detectors.
Another thing if cars are moving very fast 150KM/H. does it have any effect on receiver reception by dynamic/static transmitter.
If it was only two or three cars, tones would be a very simple solution.
For fifty cars, serial digital data transmission of actual numbers would be much better.
If all cars set of in the receiving mode, when the first car crosses the line, it transmits its number and a "time =0" code. This starts off the timers in the other cars. As they cross the line, their timer is stopped and they then transmit their number and the delayed time. if the message is not acknowledged, the message is repeated after a delay.
Radio waves travel at the speed of light. Cars don't move fast enough to contribute any effect in that area.