Radio triggered linear positioning for trains (fsk/8051)

[PlaneMad]

Hi, im sort of lost trying to figure out how to implement my graduation project idea. the goal is to design a system that will give passengers inside trains the current location of the train and other details like next station, delay, ETA etc without using a gps. i figured i could take advantage of the linearity and predictability of a train's route to build this system using simple radio communication instead of using gps systems. the focus is on low cost and scalability on a huge railway network

the principle is simple: if a train already has the information of the route preprogrammed, you just need some sort of external trigger from waypoints outside as well as knowledge of distance travelled to estimate the current position of the train.

so there will be a short range radio transmitter at every station that will continously transmit its unique 4 letter station code (for the project, its just 3bits). this is very similiar to non directional beacons used for aircraft communication.

onboard the train, the receiver will continously monitor the particular frequency for a station signal. once within range, the station code is matched to the timetable database in the microcontroller. with this info and data from the trip odometer its possible to estimate the current position of the train. the resulting info is displayed to the passengers

ive made a simple animation to illustrate the concept
**broken link removed**
**broken link removed**

ive been doing a lot of reading in the college library and ive kinda figured that fsk modulation would be the ideal choice for transmitting a 3bit code for a distance of around 2km. would this be correct? ive been searching all through the net but ive not found any circuits for what seems to be a very simple requirement. all i can find are fm circuits but i dont know how exactly to modify it for fsk. any help appreciated.

cheers

 

[PlaneMad]

hmm, maybe i sounded too complicated. anyway, the requirement is to transmit a 3bit binary code over a distance of 2km. whats the best way to do it?

 

[PlaneMad]

i would have thought a simple fsk radio circuit will be simple to find, but doesnt seem like it are there any specific sites for such radio circuits?

 

[blueroomelectronics]

At 2km you could take a look at the 9x series of XBee radios.

PS nice diagram. What did you use to draw it?

 

[PlaneMad]

thanks bill. i read up on exbee and i understand that its similiar to bluetooth and can be used to build peer to peer networks. its seems like a waste of resource to go to that sophistication when all this requires is one way transmission of tiny data (3bits). so stuff like error control and such is quite unnecessary.

but anyway, our aim at the moment is to demonstrate the concept that positioning can be done without gps and not actual implementation in a train. so theres no worry about interference from atmosphere etc. and we are not looking at robust communication equipment as yet. just about any system that can wirelessly transmit a 3bit code. and since we will be testing it out in a lab, a range of 10m is sufficient at the moment. so we are dumbing it down as much as possible since we dont really have too much time for development, just around a month.

thanks, made the images in illustrater and animated in photoshop. check my wikipedia profile for more of my work

 

[blueroomelectronics]

For a few meters the simple 433 kHz radio modules should do the trick
Radiometrix UHF Radio Telemetry Transmit Module

 

[PlaneMad]

awesome bill, thanks a ton. im wondering if we can build the circuit ourselves, cause we are discouraged from buying kits (another reason for dumbing it down ) this actually seems perfect for actual usage with trains. but if we buy this kit, we really dont have much else to show as our own work to the college. any other suggestion that will let us have a little more hands on experience with building circuits?

 

[PlaneMad]

and one more thing, im still not too clear about the fsk modulation part. would it require a custom fsk circuit, or can a fm transmitter circuit be modified to implement the fsk modulation?

i have only been able to find fm circuits in books and the net, but for fsk all i can find are block diagrams.

 

[Nigel Goodwin]

awesome bill, thanks a ton. im wondering if we can build the circuit ourselves, cause we are discouraged from buying kits (another reason for dumbing it down )

It's not a matter of buying a kit, the RF modules are ready built and licence free (it's essentially just another component) - building your own would mean they would probably be illegal to use, and potentially unsafe.

 

[PlaneMad]

It's not a matter of buying a kit, the RF modules are ready built and licence free (it's essentially just another component) - building your own would mean they would probably be illegal to use, and potentially unsafe.

true, but then again. this wont be demonstrated in the open. its more of a lab project so licensing is not an issue. at the end of it, we want to learn a few things about radio fundamentals, buying a kit would deprive us of that.

i have read plenty of articles about people building their own wireless systems, and we are looking for something that does a very simple thing - transmit a 3bit binary code over 10m. so im sure there is an easy diy circuit to do that

 

[blueroomelectronics]

They are very inexpensive modules. Cheaper than building one.